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Thread: Audio Dictionary

  1. #1
    Registered User wizeguy4's Avatar
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    Audio Dictionary

    Sticky Please?

    Ok here is a list of audio terms. Not all of them are strictly car audio, some are just audio. But anything related to sound reproduction is here. Fell free to add to it.


    A-B Test
    A test by which an observor subjectively compares the performance of two components of the same type; for example, a test between two different speakiers. For the test to be scientifically valid, the inputs, levels, and listening conditions should be matched.

    ABX Comparator
    A device that randomly selects between two components being tested. The listener doesn't know which device is selected.

    Acoustic feedback
    A phenomenon where the sound from a loudspeaker is picked up by the microphone or other transducer, like a phono cartridge feeding it, and re-amplifys it through the same loudspeaker only to return to the same microphone to be re-amplified again, etc.. Each time the signal becomes larger until the system runs away and rings, or feeds back on itself producing the characteristic scream or squeal found in sound (mostly, PA) systems. These buildups often occur at particular frequencies called feedback frequencies.

    Acoustic Suspension (enclosure)
    A Sealed box system that uses the resistance of the internal air of a sealed enclosure to control the motion of the cone. Sometimes known as an infinite baffle type.

    Sound is simply vibrating air. How fast, how much, and when the air is vibrated, determines what we will ultimately hear as sound. The science of this process is called acoustics.
    When a speaker cone (or anything else that has the ability to vibrate in the auditory range) moves forward, the air molecules in front of the cone are compressed, causing the molecules to form an accelerating wave forward. This continues to happen until the speaker cone moves in the opposite direction, which causes a rarefaction (or thinning) of the air mass between the speaker and the listener. This is the basic concept of how sound waves are produced.

    A word prefacing certain circuits in which the processing is performed by use of transistor or tube juctions, rather than passive componenets such as resistors, capacitors, and coils. Such items as crossovers and equalizers may be constructed either way. Active processing usually affords more more options, and greater precision, albeit at greater cost.

    Active Display
    A special feature for front panel receiver displays that generates animated patterns for both segmented and dot matrix LCDs that proceed the sequential display of information such as clock, CD titles, and radio station call letters and frequencies.

    (audio coding 3) Dolby's digital audio data compression algorithm adopted for HDTV transmission and used in DVDs, laserdiscs and CDs for 5.1 multichannel home theater use and automotive surround application.

    Adaptive Reception
    A circuit that provides adjustable delay such that the time at which a sound wave is produced from various signal channels can be changed. This allows synchronization for each channel of a multi-channel output device, so that sound waves from multiple speakers will converge at approximately the same time at a single point in space (the listener).

    Air Gap
    In a speaker's motor section, the space between the top plate and the pole piece. This is where the magnetic flux field is concentrated and where the voice coil interacts with it..

    Alternating Current
    Electricity which flows in opposite directions, alternating at a certain rate (Hz). As supplied by power companies, AC in the United States alternates 60 times per second and is deemed as 60 Hz power. However; some countries have a 50 Hz system, and ships and aircraft may use 400 Hz.

    Alternator Whine
    A siren-like whining that appears as the rotational speed of an engine increases. The noise is usually the result of a voltage differential created by more than one ground path or a poor ground path to the affected equipment.

    Ampere is a unit measurement of current of electrical energy equal to one coulomb of charge per second. Most DC applications refer to positive current - current which flows from a positive potential to a more negative potential, with respect to a reference point which is designated as zero or neutral potential (usually ground).
    The electrons in a circuit flow in the opposite direction as the current itself. Ampere is commonly abbreviated as "amp", not to be confused with amplifiers, of course, which are also commonly abbreviated "amp". In computation, the abbreviation for amperes is commonly, "I".

    A device, either a single stage or a large scale circuit with mutiple stages for creating gain, ie. making small signals larger.

    Amplification Classes.
    All sound is a sinosoidial waveform. It has alternating peaks and valleys. The center point of each wave is the zero, or switching point that separates the positive (top) from the negative (bottom) portion of each wave. When a tube or transistor amplifier operates in Class A, the output tubes or transistors amplify the entire waveform without splitting it into positive and negative halves. In Class AB, used in the overwhelming majority of amplifier designs, the signal is split into two halves, positive and negative, and each half is sent to a tube or transistor circuit for amplification. Both sides work in tandem, and the two halves are recombined at the output section to reconstruct the whole signal. This technique increases the amount of power that can be applied, but increases distortion. Class A amps usually provide lower, often imperceptable distortion, but at the expense of reduced power output.Class D or High Current operation is essentially rapid switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle. Theoretically, since the output devices are either completely on or completely off they do not dissipate any power. If a device is on there is a large amount of current flowing through it, but all the voltage is across the load, so the power dissipated by the device is zero; and when the device is off, the voltage is large, but the current is zero. Consequently, class D operation (often, but not necessarrily digital) is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product yet to be made; meanwhile designs do exist with efficiencies approaching 90%. This is a design that is increasimgly popular for use in bass systems, where maximum power is necessary, and slightly elevated levels of distortion are easily tolerated.

    The strength or intensity of an AC signal applied by the amplifiers output to a speaker's input. Also, a measure of the relative power of any variable recurring phenomenon. Typically, measurements are made in Decibels.

    Amplitude Modulation (AM)
    In radio broadcasting, amethod of modulation in which the amplitude of the carrier voltage is varied in proportion to the changing frequency value of an applied (audio) voltage. (Also see Frequency Modulation).

    Automatic Music Search. A feature that allows a CD or cassette mechanism to skip forward or backwards to another track.

    An electrical signal in which the frequency and level vary continuously in direct relationship to the original acoustical sound waves. Analog may also refer to a control or circuit which continuously changes the level of a signal in a direct relationship to the control setting.

    Analog Switch
    A hardware-oriented switch that only passes signals that are faithful analogs of transducer parameters.

    Angled (box or enclosure)
    A type of speaker enclosure wherein the woofers, or Drivers, are situated in a box that is angled on one side. This is usually done to facilitate a more direct coupling of the upper part of the speaker's range to the listening environment.

    Anechoic chamber
    A special room that is constructed without acoustically reflective surfaces, such that it is without echoes, or an-echo-ic. This experimental setup enables engineers to more precisely measure the acoustical properties of many types of equipment. A real life anechoic situation is experienced by skydivers. However, they may be a bit distracted from the experience by the approaching ground.

    The electrically positive pole of an electronic device such as a semiconductor. A diode, for instance, has a positive and a negative pole; these are known as the anode and the cathode.

    A device, such as a rod or wire, which picks up a received radio frequency signal or radiates a transmitted RF signal.

    Refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but to yeild a smoother response pattern by lowering the Q of the system and reducing the impedance peak at resonance. Most restrictive ports are damped with quantities of sound absorbtive material.

    Automatic Tuner Activation. A feature that allows the tuner to be accessed while a tape deck is rewinding or fast forwarding.

    Adaptive Transformation Acoustic Coding. The process used in MiniDisc that utilizes psychoacoustic principles to limit quantization noise and reduce the data quantity from 16 bits to 4 bits by using non-uniform frequency and time division.

    The act of reducing the Amplitude or intensity of a signal. In speaker systems, high frequency drivers are commonly more efficient than low frequency drivers. This creates a need to adjust the driver levels to create a uniform overall frequency response. L-pads are commonly used for many passive systems

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    Average or apparent power
    The result of multiplying the rms value of the voltage by the rms value of the current in an electronic circuit. It is expressed in watts (W) for resistive loads and in voltamperes (VA) for reactive loads. The real power is usually less because of losses when the power factor is accounted.

    1. Of, or relating to, humanly audible sound, i.e., audio is all the sounds that humans hear. 2. a. Relating to the broadcasting or reception of sound.
    b. Relating to high-fidelity sound reproduction.

    Audio Frequency Spectrum
    The band of frequencies extending roughly from 20 Hz to 20 kHz and encompassing the full range of normal human hearing.

    A species of dedicated audio nut who actually reads definitions like this.

    Auto Memory
    A tuner feature that automatically finds the strongest stations in the local area, and places them in preset memories


    Back Plate
    The part of the woofers metal Basket or frame on which the Magnet structure is mounted.

    Back Light
    In receivers, a display may be lit from the rear to create better visibility under a wide range of ambient light conditions.

    A flat panel that divides the front and rear sound waves produced by a woofer. Sometimes baffle is used to mean an enclosure or the front panel on which the speaker is mounted .

    Balanced wiring
    Audio line signals require two conductors. In an unbalanced line, the shield is one of those. In a balanced line, there are two internal wires plus the shield. For the system to be balanced requires output transformers and usually employs XLR connectors. Balanced lines are less apt to pick up external noise. This is usually not a factor in home or car audio, but is a factor in professional audio requiring hundreds or even thousands of feet of cabling.

    Bandpass (box or enclosure)
    An enclosure that is specifically tuned to give maximum energy to a very limited range of frequencies, usually the lowest. In this arrangement, the woofers are fully enclosed in the box with the sound pressure being vented through one or more ports.

    Banana Jacks & Plugs
    A set of connectors in which 4 spring contacts are wrapped vertically around a central pin like a banana peel. When inserted into the receptacle jack it maintains a strong and consistent contact. This type of connector is highly regarded as an excellent and reliable interconnector for cables between amplifiers and speakers.

    Band-limiting filters
    A low-pass and a high-pass filter in series, acting together to restrict (limit) the overall bandwidth of a system. Many audio amplifiers and processors, having switches labeled as "Rumble" or "Hiss," are filters of this type.

    Bandpass filter
    A filter that has a finite passband, neither of the cutoff frequencies being zero or infinite. The bandpass frequencies are normally associated with frequencies that define the half power points, i.e. the -3 dB points. In multi-driver speaker systems, the Midrange driver may be fed by a bandpass filter.

    Bandpass Gain
    The increase (or decrease) in efficiency of loudspeakers, due to the enclosure size and tuning. This is measured by the midband sensitivity of the speaker as a whole.

    Abbr. BW The numerical difference between the upper and lower -3 dB points of a band of audio frequencies. Used to figure the Q, or quality factor, for a filter.

    Barium Ferrite
    A speaker magnet material made from an alloy with iron and barium for improved magnetic strength.

    The metal frame structure of a standard dynamic loudspeaker. In larger, heavier speakers, this may be made of cast metal for extra strength and rigidity. All the other elements of the speaker are mounted on this structure.

    The portion of the audible sound spectrum that contains the lowest frequencies. These frequencies have the longest wavelength and require considerably greater electrical power to render them at their original strength. In a good modern speaker system, the bass portion of the response curve extends from as high as 500 hertz, down to 20 Hz.

    Bass Boost/Enhancer Circuit
    An active low pass amplifier section added to some receivers, equalizers, and amplifiers that allows as much as an 18 decibel boost to be applied to an audio signal in the low frequency 35 to 90 Hertz range.

    Bass Reflex (box or enclosure)
    A speaker box design that makes use of a port or Passive Radiator which allows the energy derived from the motion of the back of speaker cone to be redirected in such a way as to reinforce the front radiation. This smooths and extends the low frequency response, but the effect is sharply Rolled Off on the low end, as the port signal goes back out of phase with the front. The overall effect of this is to tune the bass response to a particular point on the lower end of the spectrum, below which it rolls off sharply.

    BBE 1 & 2 Processing
    A signal processing circuit that provides improvements in imaging and spatial realism by altering the frequency and phase characteristics of portions of the input signal.

    Abbr. b, B Ten decibels. ( In honor of Alexander Graham Bell.) The Bel was originally a unit measure of the amount a signal dropped in level over a one-mile distance of telephone wire. See: decibel

    Bessel Alignment
    A particular crossover configuration which offers superior phase coherence in exchange for slightly lower output level match.Bessel: A design that places emphasis on phase and transient response over reducing ripple.

    Some speaker systems with multiple drivers do not contain a crossover network, and they require a separate amplifier for each frequency range. The bi-amplified system still requires an active crossover network to send the proper frequency band to each amplifier and speaker, but it is in the circuit preceding the amplifier and speaker and does not handle the power output.

    Bipolar Transistor
    A older but still effectively used transistor type that contains two p or n junctions or diodes between two layers of opposite polarity material (emitter and collector) . In handling large power, mostly replaced by MOSFET types.

    (measured in Tesla meters) The product of a speaker driver’s gap flux density and the length of the voice coil conductor in the gap.

    Blank Skip
    A cassette feature that automatically detects blank areas of the tape over a set number of seconds in length and activates Fast Forward, until either the end of the tape, or audio information is reached.

    A type of high precision connection often used in instrumentation and sometimes in digital audio. BNC connectors sometimes are used for digital connections such as from a CD Transport to the input of a DAC.

    Usually refers to excessivly reverberant bass response, or a peak in the bass response of a recording, playback, or sound reinforcement system.

    Another, and common name for a standard speaker enclosure. There are many variations in type, which are basically compromises between size, power handling, cost, frequency response, and many other considerations.

    Bridge Mounted (2 & 3-way speakers)
    In combined 2 and 3-way speakers, which have woofers together with a Tweeter, or a Tweeter and a Midrange Driver, the smaller drivers are attached to the woofer by either one of two standard mountings.

    The bridge-mount method has a metal or plastic bridge running from one side of the woofer's outer perimeter to the other. The smaller driver or drivers, together with the Crossover network, is then mounted on the bridge. The advantage of this arrangement is that the woofer is left intact with no exposure of the voice coil or other internal elements. On the negative side, there is more covered surface area that marginally reduces the output at certain frequencies, and makes it a little more difficult to mount the unit.

    The post-mount method provides a post that is attached to the center of the inner magnetic pole, to which the other drivers are then mounted. It has a reduced obstruction to woofer dispersion, but it does require a hole in the Dust Cover/Cap that can give environmental access to the woofer's inner workings. This creates the possibility in some less well designed units of operational degradation from airborne particles over time.

    Bridged Power
    Bridging an amplifier, combines the power output of two channels into one channel. Bridging allows the amplifier to drive one speaker with more power than the amp could produce for two speakers. Because of this high power output, bridging is the best way to drive a single subwoofer.

    If the amp is bridgeable, the owner's manual will have directions that tell you how. Usually, an amp is bridged by connecting the speaker leads to the positive (+) terminal from one channel and the negative (-) terminal from the other channel. However, be sure to consult your owner's manual before attempting to bridge your amp!

    Also, keep in mind that most amplifiers need to see a 4-ohm load when bridged to mono operation. When bridging an amplifier, use one 4-ohm speaker or, if you prefer multiple woofers, connect two 8-ohm speakers in parallel. Again, consult your manual before operating your amp in bridged mode.

    Bridged, Transformer Less. A circuit design wherein two small Integrated Circuit (IC) amplifier channels are bridged together to provide a single, larger output circuit. These circuits are limited by their current capabilities and the amount of heat they generate.

    Best Tuning Memory. A feature in which the tuner selects radio stations by signal strength, and assigns them to presets in numerical order, according to their frequency value.

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    Built-in Crossovers
    Frequently used to limit the high-frequencies reaching a subwoofer, a low-pass filter crossover allows only frequencies below the crossover point to be amplified. A high-pass crossover allows only frequencies above the crossover point to be amplified — used to keep destructive low bass away from small speakers, so they can played safely. Crossovers may be variable or selectable. Continuously Variable means the crossover circuit can be adjusted to any frequency between the listed end points. Selectable means that any of several preset crossover points can be chosen to accomodate variuous driver (speaker) designs.

    A method of woofer construction in which the rear suspension system is anchored a little further back by designing the back plate so that it is press stamped, or cast, outward. This allows greater Excursion of the voice coil, and prevents "bottoming out," which is very destructive to the coil form when large signals move the voice coil beyond its range limits. This technique does not eliminate the problem, but does help to reduce it.

    Bumped & Vented
    See discussion of Bumped above. Many higher power speakers have a vent hole in the center Pole Piece of the magnet. When viewed from the back, there is usually a screen over the hole to prevent debris or particles from falling into the voice coil gap. But it does allow for greater ventilation of the motor section, and this in turn provides for higher power inputs by permitting greater heat dissipation for the voice coil assembly.

    Bullet Horn (tweeter)
    A type of tweeter in which the radiator has a large passive, bullet-shaped device above its center that extends the nominal dispersion angle of the sound, thus allowing it to cover a greater area with high frequency radiation

    A type of rubber used for speaker surrounds. Butyl has very good damping characteristics and is resistant to UV contamination from the sun.

    Butterworth crossover
    A type of crossover circuit utilizing low-pass filter design characterized by having a maximally flat magnitude response, i.e., no variation in the amplitude response in the domain of the passband


    The property of an electric device that permits the storage of energy as a result of electric displacement when opposite surfaces of conductive plates are maintained at a difference of potential. In a capacitor, capacitance is the measure of the property (the amount of charge that can be stored) equal to the ratio of the charge on either surface to the potential difference between the surfaces. Capacitance is measured in Farads, or micro-farads.

    Capacitor (Power audio)
    Power stabilizing capacitors store the necessary power amplifiers need to punch larger bass notes while limiting clipping. They store energy during intervals when it is not required, which is most of the time, and release it when demand exceeds what is available from the car's power system.

    CD Compact Disk
    The most popular format for conveying music and data currently available. It is among the first digital media to take over from the analog formats of phonograph records and tapes; coming to the market in the early 1980's. Developed by Phillips, Sony, and Pioneer, it records information on the now familiar shiny discs by deforming the inner metal foil on the disc with tiny micro pits burned in by a laser. These pits taken together, form a binary digital code, which when converted to bits, then bytes, can recreate the original information, such as audio. It's superiority as a format, consists of the fact that the process gets around the such problems as: noise, hiss, pops, transducer irregularities, and other audible problems that made analog carriers a less than fully high fidelity mode. Dynamic range exceeds 100 decibels, a sufficient soft/loud difference to make the reproduction very lifelike. Frequency response is at the theoretical limits of human hearing and unwanted aural artifacts are generally below the threshold of perception. The only significant improvement is the DVD borne addition of multiple channels, to recreate the original sonic environment. In short, it's the best thing to come along since Mozart sat down at the piano.

    CD Controller
    This is a device that can exist either incorporated into a car stereo receiver (head unit) or as a separate module. In either case in contains the operating controls necessary to use a CD player or changer. This will usually include but is not limited to such favorites as: play, stop, FF, REW, pause, Track, and disk. As with a good many other things, most controllers and the units they control are incompatible with any model other than the one they were made for. There are the occasional rare exceptions, but yours is not likely to be one of them.

    CD Head Unit
    Is usually a single disc player installed as a separate unit (not including a radio receiver). These are increasingly uncommon.

    CD Receiver
    Multiple function receivers are most commonly configured with radio and CD player capabilities in standard car receiver (head end) units. These may include cassette tape decks as well, and may also have high power amplifiers (over 15 watts RMS) installed in them. Some units may even have mini 3 to 5 disc changers in them. Among common and desirable features are:
    Four speaker outputs with a fader control to balance front and back; Bass and Treble controls; Left right balance; 12 or more presets for AM & FM stations; Random play for the CD; digital clock. FM mono sensitivity should be at least 13dBf. Preamp outputs are desirable: minimum output voltage should be at least 1.8 volts. Also, audio line inputs for the CD changer you may want later. Remember that RMS output power is usually no more than half of the "peak power" rating.

    CD Changer
    Separate units that may allow the user to hear any of 3 to 120 discs, or more in whatever order they wish to program them, or to skip from one track to another, or from one disc to another. Many of these come with separate controller units that allow for user operation and programming. Some are built to take advantage of controller systems built in to many receivers expressly for that model. Many also have a device called an FM modulator that permits connection to any standard FM stereo radio. The signal can be heard on whatever unused frequency the radio is tuned to. Most changers also permit direct audio outputs to any standard RCA high impedance, line level, input. This is the preferred input to avoid noise and distortion that may occur with radio usage.

    Common name for a complete amplifying stage in any audio amplifier. Most amplifiers are denominated as 1, 2, 4, 5, or 6 channel units. Each of these is a discrete audio amp on its own, capable of taking a small line signal input and amplifying it sufficiently to be heard on an appropriate speaker. Some amplifiers are capable of bridging two channels together, to form one channel of double the power of each separately. The manufacturer's instructions differ widely on how to accomplish this, and each must be followed exactly.

    Chebyshev Filter
    A filter that has some ripple in the pass-band but has an initial attenuation slope which is steeper than a Butterworth filter.

    A signal that results from an amplifier that is either overloaded or underpowered relative to the signal Amplitude it being asked to generate. A clipped waveform is one in which the gently rounded peaks and valleys of the AC audio wave are instead sliced off or clipped, to yield what looks a lot like a square or alternating DC wave. When DC is applied to a speaker, the voice coil has no means of propelling itself relative to a constant magnetic field. Instead, it can only convert the incoming current to heat, and ultimately burns up. The effect of alternating DC on speakers is remarkable, irritating, painful, and short. If you are able to hear evident Distortion at high volume levels, or smell smoke, reduce the volume. It may already be too late for your speakers, but at least you may be able to save the amplifier.

    Coaxial Cable
    A single copper conductor, surrounded with a layer of insulation, covered by a surrounding copper shield and finally, an insulating jacket. A constant-impedance unbalanced transmission line. In audio, this type is commonly used for low level, line, signals terminated in RCA plugs.

    A term used to describe levels of audio Distortion that cause serious departures from a true High Fidelity rendition of the original signal.

    The measurement in liters or cubic feet of the volume of air that is equal to the compliance, or maximum extension of a speaker's total suspension.

    Component System
    This term is used in relation to speaker systems, to indicate a system in which separate mounting arrangements are provided for each component of the system. In a typical car system you might see a woofer in a box in the rear, midranges at the side and tweeters mounted on the dash panel. This compares to the typical integrated speaker enclosure in which all the Drivers are mounted in the same box.

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    Compression Driver
    Compression drivers are usually dynamic; that is, with a magnet and interacting coil arrangement, and a small diaphragm as the main transducer. These are the motor parts, also known as the driver, of a compression horn tweeter or compression horn general-purpose speaker, such as those used for Public Address (PA) purposes. These drivers are usually coupled to the throat of an exponential horn. Such an arrangement enables this type of tweeter to have very high directional characteristics, which allows them to be especially effective in situations requiring a very wide sound field. In typical home and car stereo near-field applications, large horns can be a bit too narrowly directional to be practical. For this reason, compression horn systems are usually found only in special purpose speakers used in mid and wide field applications such as PA systems or the sound systems installed in large theaters. However, some specialized horns have small apertures and very shallow horns, and can be quite suitable for close spaces.

    Comb Filter Effect
    This acoustical and electronic effect occurs when two signals interact in such a way as to produce an irregular spiked and choppy response pattern. When graphed on paper, this pattern looks like the teeth of a comb, hence the name. This effect is frequently the product of overlapping outputs from the various drivers in the system. It can develop in either a single speaker between the individual drivers, or between unmatched sets of speakers. This same effect can also be produced by wall reflections and other room anomalies. The usual remedy for this, if it becomes objectionable, (not every instance is even perceived as such) is to make sure the Crossover set points are appropriate for the drivers being used, or that the crossover is operating correctly. Obviously, one should also use only compatible speaker sets.

    1. An increase in density and pressure in a medium, such as air, caused intermittently by the passage of a sound wave. 2. The region in either air or material in which this occurs.

    Compression Wave
    A wave propagated by means of the compression of a fluid, such as a sound wave in air. To create sound, the opposite state of rarification alternates with the crest of every compression.

    Constant Directivity (CD) Horn
    A horn-loaded high frequency driver that exhibits more or less constant distribution of high-frequency sound in the horizontal direction. This is done by using one of several special dual shaped horn designs created to solve the traditional problem of horn-loaded driver output varying with frequency. All CD horns exhibit a high frequency roll-off of approximately 6 dB/octave beginning somewhere in the 2 kHz to 4 kHz area.

    An amount of electrical charge which contains 6.24 x 1018 of electrons. So there!

    A device or passive circuit used in systems with separate tweeter and/or midrange Drivers. It Rolls Off frequencies above and below certain points in the range, to allow the sound to be tailored for the specific driver to which it is sent. Most speakers have crossovers that consist of passive elements such as capacitors, coils, and resistors to separate the various frequencies. In a bi-amped or multi-amped system, the crossover is an active device that feeds the various frequency bands to the inputs of the amplifiers that operate the individual drivers.

    Crossover Frequencies
    The frequencies at which a passive or electronic crossover network divides the audio signals, which are then routed to the appropriate amplifiers or speakers.

    Crossover Network
    A unit which divides the audio spectrum into two or more frequency bands (Also see Crossover Frequencies).

    Crossover Slope
    The rate at which a crossover circuit attenuates the blocked frequencies. Slope is expressed as decibels per octave. A 6dB per octave crossover reduces signal amplitude level by 6dB in every octave starting at the crossover point. This means that every time the frequency of the audio signal is changed by a factor of 2 (one octave), the level of the audio signal is attenuated by 6dB. For example, if a low-pass crossover is set at 60Hz with a 6dB slope, you'll see a drop in level of 6dB at 120Hz. With slopes of 12dB and higher, the output beyond the crossover point will be reduced to below the level of audibility.

    Cross Talk
    1. Undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or channel, to another. 2. Any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Note: In telecommunications, cross talk is usually distinguishable as speech or signaling tones.

    The volume or quantum of the flow of electrons through a conductor, as opposed to voltage, which is the measure of the intensity or velocity of the electrical flow.

    Custom File
    A feature package that provides intuitive and safe source management for an audio and A/V system. Examples include Disc Memo, Selection, Station Memo, and Memo List.

    Cutoff Frequency Filters
    The frequency at which a signal falls off by 3 dB (the half power point) from it's maximum value. Also referred to as the -3 dB points, or the corner frequencies


    DAC (D/A)
    Digital to analog converter. An IC component or circuit that is used to derive or convert an analog signal from a digital one.

    Part of the suspension connected to the bottom of the speaker cone at the voice coil that centers the voice coil in the magnetic gap. It is sometimes referred to as the spider

    As Newton observed, an object once set in ,motion will keep on moving unless a restrictive counterforce is applied. Damping is that force at work in the mechanical resistance that is applied to a speaker cone to keep it from resonating in the absence of an input signal. It is also the factor that is applied as a control voltage by the amplifier for the same purpose. These measures help reduce or dampen Harmonic Distortion. This also improves bass accuracy.

    Damping Factor
    The ratio of rated load impedance to the internal impedance of an amplifier. The higher the value, the more efficiently an amplifier can control unwanted movement of the speaker coil. A high damping factor is crucial for large speakers that reproduce bass. Usually the higher the number, the better, although it is debatable if anything over 50 is audible. Damping factor is calculated by dividing the load (speaker) impedance by the output impedance of the amplifier. Thus, a given amplifier’s damping factor will decrease as the speaker’s impedance decreases. This means an amp optimized at 4 ohms will provide tighter bass than at 2 ohms.

    DC/DC Converter
    Since 12 volts limits the amplitude of an audio signal, a group of components within an amplifier converts battery voltage (DC) into AC so that it can be increased by swetching devices and a transformer, and converted back to DC (rectified). This provides higher voltage to drive the amplification stage to higher power. Also called the Power Supply circuit.

    Decibel or dB (see also Efficiency and Sensitivity)
    One tenth of a Bel. This is a measurement of the comparative strength of two powers, and can be applied when measuring any signal in the audio, video, and electromagnetic spectrum. If two powers differ by one Bel, there is a difference of 10 times the power. If comparing amplifiers, where one is rated at 10 watts while the other is 100 watts, then we have a difference of 10 decibels, or one Bel. Decibels should be understood as ratios, not fixed quantities.

    Decibels are the preferred method and term for representing the ratio of different audio levels. It is a mathematical shorthand that uses logarithms (a shortcut using the powers of 10 to represent the actual number) to reduce the size of the number. For example, instead of saying the dynamic range is 32,000 to 1, we say it is 90 dB [the answer in dB equals 20 log x/y, where x and y are the different signal levels]. Being a ratio, decibels have no units. Audiologists generally assert that 1 decibel is the smallest difference in volume that can be heard by the average person. The term is derived as an honor to Alexander Graham Bell, who invented the telephone, and did much of the preliminary work in the modern science of acoustics.

    A signal processing device or circuit used to delay one or more of the output signals by a controllable amount. This feature is used to correct for loudspeaker drivers that are mounted such that their points of apparent sound origin (not necessarily their voice coils) are not physically aligned. Good delay circuits are frequency independent, meaning the specified delay is equal for all audio frequencies (constant group delay). Delay circuits based on digital sampling techniques are inherently frequency independent and thus preferred.

    Destructive Interference ( phase cancellation)
    A phenomenon that occurs when speakers are 180 degrees out of phase, i.e., what one speaker is trying to produce, the other speaker is fighting to cancel. One speaker's wave is in the positive phase (rarefaction), while the other speaker's wave is in the negative phase (compression).

    This term describes the sound-producing element in a tweeter, or Horn. This is the surface that produces the sound you actually hear. The motor that drives it can be any of several technologies including Piezo, conventional dynamic, or ribbon types. Diaphragms do not produce low and low midrange frequencies well, so they are not usually found in that application.

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    Die Cast (basket)
    A type of speaker basket or frame that is cast as a single piece of relatively thick, rigid metal. This contrasts with a Stamped frame that is shaped by pressure, much like a car body fender. Cast metal is heavier and more rigid, and thus less likely to "ring" at certain frequencies, and will hold its shape somewhat longer against the pull of gravity. This is mainly advantageous in the larger woofers of 12" or greater. Smaller drivers will likely not benefit perceptibly from being cast.

    Widely spread out or scattered; not concentrated.

    A commercial device like a lens or grillwork that diffuses, or scatters sound

    Digital Technology
    Human beings directly process information in an analog format. That is, our senses directly convey information to the brain in the form of constantly varying amplitudes and frequencies that approximate the impact of outside stimuli upon the receptors (eyes and ears, etc.) of the organs involved.
    Digital technology is a method of translating this same information in the form of packets (bytes and bits) of numerically equivalent values. This enables input transducers (microphones, cameras, chemical sensors, etc.) to produce differential waveforms that can be reduced, down to the smallest differences, to a number. This number is transmitted to a receiver with a digital to analog converter that allows the original analog information to be reconstructed for the benefit of our human brains. This is of course an egregiously simplified explanation of the most significant technology of the present time. We invite you to explore more this topic deeply, not just for audio/video, but to understand the new world we have entered.

    Acronym for Deutsche Industrie Norm (Deutsches Institut fuer Normung), the German standardization body. A world reference standard for the mounting parameters of many common receivers ( Head ends) as well as other types of cables and equipment.

    Direct sound
    Sound that arrives at the listeners ear first.. Sound reaching the listening location without reflections, i.e., sound that travels in the most direct path from the source to the listener.

    Discrete Output Devices
    A separate active unit in an amplifier, capable of performing a single essential function within the output circuit. There are three basic types of output devices found on car audio amplifiers — integrated circuits, bipolar transistors, or MOSFETs. Integrated Circuits (or IC)are found only on relatively low-wattage (20 watts RMS per channel or less) amplifiers and receivers. An IC incorporates many functional devices and thus is not considered a discrete output device. Most cannot handle more than 25 watts RMS.
    Bipolar transistors and MOSFETs are found on the output stages of high powered amplifiers. They are fast enough and can handle enough current to provide power in excess of 20 watts per channel to speakers. Both of these types of transistors are considered discrete output devices. Usually there are two per channel, but some amps feature as many as eight per channel.

    The extent to which a sound emitter yields acoustic radiation over a given area. This is a particular concern in tweeters and midranges whose portion of the audio spectrum has a much more directional character than woofers. Many Horn tweeters, while very energetic, have a more limited area of dispersion within which their effect can be fully perceived. Generally, Dome tweeters can be heard over a much wider area, all other factors being equal. But each particular example must be assessed individually for this factor. Some radiator designs are better than others.

    The measurement of cubic volume that an item (such as a speaker or port) takes away from the internal volume of an enclosure. When designing an enclosure, this figure must be added to the enclosure volume .

    Any departure from a true and accurate reproduction of the original waveform. It can include Noise, Clipping Distortion, Harmonic, and Intermodulation Distortion. These last two forms are fairly common in loudspeaker reproduction and can be reduced but not entirely eliminated in the existing technology. It would be fair to say that modern amplifier design fairly eliminates nearly all forms of inherent perceived distortion, leaving only that caused by inappropriate user settings and overloading.

    Distortion is the name given to anything that alters a pure input signal in any way other than changing its size. The most common forms of distortion are unwanted components or artifacts added to the original signal, including random and hum-related noise. Distortion measures a system's linearity - or nonlinearity. Anything unwanted added to the input signal changes its shape (skews, flattens, spikes, alters symmetry or asymmetry). A spectral analysis of the output shows these unwanted components. If a circuit is perfect, it does not add distortion of any kind. The spectrum of the output shows only the original signal - nothing else - no added components, no added noise - nothing but the original signal.

    It's rather amusing to see amplifier manufacturers making great claims about the advantage of the extra .001 % Distortion they've wrung out of their products, while most speakers are considered very good if they can keep such distortions below 5 %. It's true that the reduction of any distortion anywhere is a positive contribution to the goal of high fidelity, but the disparity between the two technologies in this regard points up the largely subjective nature of many such claimed advantages.

    Diversity Tuner
    An FM tuning method which employs two antennas. The tuner can switch between the two antennas in order to attain better reception.

    Dolby Digital®
    Dolby's name for its format for the digital soundtrack system for motion picture playback. Utilizes their AC-3 method of digital compression. The signal is optically printed between the sprocket holes. Introduced to Home Theater on laser disc and DVD and CD. Dolby Digital may use any number of primary audio delivery and reproduction channels, from 1 to 5, and may include a separate bass-only effects channel. The designation "5.1" describes the complete channel format. Surround decoder systems with Dolby Digital automatically contain Dolby Pro Logic processing to ensure full compatibility with the many existing program soundtracks made with Dolby Surround encoding.

    Dolby Noise Reduction
    Decodes Dolby-encoded cassette tapes during playback to virtually eliminate the tape hiss which is especially apparent in quiet environments. Dolby B is the most widely used system. Dolby C is an extension that is even more effective at increasing the signal-to-noise ratio.

    Dome Tweeter
    Tweeters come in several different types; cones, horns and domes being the most popular. Dome types are heavily favored in many standard applications. They are efficient, and have low Distortion and wide dispersion. There is a choice between hard and soft dome materials, but all have relatively low mass and high power handling capabilities.
    This same design in a larger form is quite effective as a midrange Driver also, and for many of the same reasons.

    Double Stacked (magnet)
    Two magnets overlaying each other to increase the overall magnetic field. In some designs for home theater applications the polarity is reversed which provides the effect of "shielding,"inhibiting the size of the magnetic field radiation, thus allowing the speakers to be used next to a television without creating Distortions on the picture tube. This is achieved without a detrimental effect on the normal power handling capabilities of the speaker.

    Dot Matrix Display
    A display type that employs regularly spaced patterned grids of point-source lighting elements. As a result, characters displayed have greater resolution than a segmented display.

    The arrangement of signal leads and wiring for optimum circuit operation, cosmetic appeal, and protective routing.

    An alternate term for: speaker, transducer, or radiator. Properly speaking, the term speaker should refer to an entire sound producing system with whatever combination of woofer, midrange and tweeter; in whatever enclosure type it is housed.

    Driver Volume
    The amount of enclosure airspace that is displaced by the speaker itself.

    DSP (digital signal processing)
    A technology for signal processing that combines algorithms and fast number-crunching digital hardware, and is capable of high-performance and flexibility.

    Many factory installed auto speakers are of the dual cone type. Sometimes also referred to as a "full-range" speaker, it uses an inexpensive, efficient design. The small "whizzer" cone in the center of the woofer reproduces high frequencies, but not with the dispersion, range, or intensity of a separate tweeter.

    Dual Channel or Dual Voice Coil (speaker)
    A woofer with two voice coils mounted to a common cone, which can be connected to separate amplifiers, to produce a common bass output. Since bass has a non-directional character, this still permits the optimum reproduction of the stereo image via other speakers. Care should be taken in making connection, to observe proper polarities, however. Failure to do so can result in the quick extinction of the Driver if the amplifiers are pulling the cone in different directions at once.

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    Dust Cover/Cap
    A rigid cardboard or plastic dome placed over the opening to the voice coil cylinder in a dynamic cone driver. The main purpose is to prevent dust from falling into the voice coil-magnet gap and causing problems. In some units it may have a slight ancillary function in extending - slightly - the midrange/ high response. Occasionally the dome may be inverted in such a manner as to extend the inner surface of the woofer and provide a very slight improvement in the smoothness of low frequency to midrange roll-off.

    Dynamic range
    The ratio of the loudest (undistorted) signal to that of the quietest (discernible) signal in a unit or system as expressed in decibels (dB). Dynamic range is another way of stating the maximum S/N ratio. With reference to signal processing equipment, the maximum output signal is restricted by the size of the power supplies, i.e., it cannot swing more voltage than is available. While the minimum output signal is determined by the noise floor of the unit, i.e., it cannot put out a discernible signal smaller than the noise. Professional-grade analog signal processing equipment can output maximum levels of +26 dBu, with the best noise floors being down around -94 dBu. This gives a maximum dynamic range of 120 dB - pretty impressive numbers, which coincide nicely with the 120 dB dynamic range of normal human hearing (from just audible to uncomfortably loud).

    Dynamic Range Suppression
    A signal compression technique which raises the level of lower passages without affecting overall volume. Especially useful with high noise levels, such as a moving vehicle.


    Effective Piston Area (Sd)
    (measured in square inches or meters) The active radiating area of a speaker cone, including that part of the surround which moves to produce an acoustic output.

    Efficiency (see Sensitivity)
    The ability of an audio system to convert electrical energy (watts) into mechanical energy (Decibels of acoustical energy). This ratio is usually given as the amount of energy measured in Decibels at a distance of one meter from the input of one watt of electrical energy. In most speakers, the greater the efficiency rating, the louder the unit will play in response to the same setting of the volume control, in comparison to less efficient types. The overall efficiency for most speakers systems is under 20 percent. Typical speakers can be rated at anywhere from 85 to 110 dB. Keep in mind, of course, that efficiency is only one parameter of a speaker's overall quality.

    Electrostatic Driver
    The Electrostatic Driver generates a motive force for its diaphragm by the interaction of electric rather than magnetic fields as is the case for the dynamic driver. The electrostatic driver is basically "hung" on a frame. It does NOT have a box enclosure, so a great deal of "coloration" (frequency response fluctuations caused by the enclosure reflections) is avoided. A large diaphragm of lightweight material is placed between two perforated (acoustically transparent) electrodes. The diaphragm is electrically polarized at a few thousand volts relative to the electrodes, which maintain a large electrostatic field. The audio signal is applied to the two electrodes in a push-pull fashion. Under these conditions, the diaphragm will vibrate in step with the audio drive signal and produce sound. Because it is a true push-pull driver (i.e. its diaphragm is driven from both front and rear), it operates in a linear fashion.

    In an electrostatic driver, the driving force is uniform over the entire diaphragm surface (note that for the Dynamic Driver, the diaphragm is driven over a small portion of its overall surface) as a result, Electrostatic Drivers do not suffer drastically from "breakup" effect as dynamic drivers. Gross distortion typically results only if the driving amplifier clips into the speaker, or when, in an attempt to play the driver at a higher sound level than its design permits, its step-up transformer may reach a point of saturation. Due to the diaphragm of the electrostatic driver being of low mass (lightweight), its transient response is excellent and reproduction of subtle, low-level musical details is exceptional.

    Electrolytic Capacitor
    A capacitor with a negative and a positive terminal that is commonly used for DC power filtration and energy storage.

    Enclosure, or Box
    A cabinet in which the various Drivers are housed. This arrangement is absolutely essential if bass response is desired from the woofer, which by itself in the open air, will produce very little low frequency response. This is so because of an effect called phase cancellation. This means that the sound wave coming from the back of the speaker at low frequencies is identical in form and intensity to the one coming from the front of the cone. When they meet, as in the open air, they are exactly 180 degrees out of phase and thus cancel each other out. An enclosure either prevents this from occurring or modifies the interaction so that the backwave actually reinforces the front wave. Tweeters and midranges are less severly effected by the phase cancellation effects, and are not in need of enclosures.

    Enclosure Volume
    The total amount of internal airspace of an enclosure. This includes the net, driver and vent volumes.

    EQ (equalizer)
    A class of electronic filter circuits designed to augment or adjust electronic or acoustic systems. Equalizers can be fixed or adjustable, active or passive. Most consumer audio equallizers divide the spectrum into 3 to 12 bands, allowing each section to be either increased or decreased in amplitude without changing the response of the rest.
    In the early years of telephony and cinema, the first equalizers were fixed units designed to compensate for losses in the transmission and recording of audio signals. Hence, the term equalizer described electronic circuits that corrected for these losses and attempted to make the output equal to the input. Equalizers permit the modification the frequency response spectrum of the signal passing through them; that is, they modify the amplitude versus frequency characteristics.

    Electronic Shock Protection. An electronic circuit that stores the audio data stream from a CD or MD in a memory buffer. If the laser pick-up mistracks, audio still flows from the buffer preventing an interruption.

    The back-and-forth travel of a cone in a dynamic Driver. How loud a speaker can play depends on how much air it can move without overheating. How much air can be moved is determined by the surface area of the cone as it moves back and forth (Xmax), the Enclosure resonance, and the suspension compliance of the motor system.

    Excursion Limited Power Handling
    Based on the maximum amount of power the driver can handle without appreciable distortion. All frequencies 30 Hz and above are considered in this limit.

    Excursion Limited SPL
    The maximum sound pressure level the system can produce given an input signal equal to the rated excursion limited power handling.

    Extended Pole Piece ( See Bumping above)
    Extended pole pieces on the magnet assembly allow for more voice coil travel, and thus lower Frequency Response, and less chance of "bottoming out"


    Farad (F)
    The basic unit of capacitance. A capacitor has a capacitance of 1F when a charge of 1 Volt across the capacitor produces a current of 1 Ampere through it. Named after Michael Faraday.

    The tuned frequency of a Vented Enclosure, measured in Hertz. A combination of the resonance frequency of the air in a Port and the resilient pressure of the air in a Ported System. Below this point the Frequency Response of a Tuned Port system rapidly Falls Off, and the system can become unstable if asked to reproduce lower frequencies at high Amplitude.

    FFT (Fast-Fourier Transform)
    A method by which a system is described using an impulse response. Both frequency and time data can be extracted, with room reflections removed, providing an extremely accurate analysis. Mathematical manipulation of the data is employed to view system parameters from a variety of perspectives.

    See acoustic feedback.

    A term used to describe the accuracy of recording, reproduction, or general quality of audio processing. Getting it "high" is every designer's goal

    Any of various electric, electronic, acoustic, or optical devices used to reject signals, vibrations, or radiation of certain frequencies while passing others. Electronically, filters can be as simple as a single capacitor, or as complex as a dedicated computer circuit. For audio use the most common electronic filter is a bandpass filter, characterized by three parameters: center frequency, amplitude (or magnitude), and bandwidth. Bandpass filters form the heart of audio graphic equalizers and parametric equalizers.

    Flat Response
    An output signal in which fundamental frequencies and harmonics are in the same proportion as those of the input signal being amplified. A flat frequency response would exhibit relatively equal response to all fixed-point frequencies within a given spectrum.

    Fletcher-Munson Curves
    Fletcher and Munson were pioneering researchers who provided the basis of High Fidelity in the '30s. They accurately measured and published a set of plots showing the human's ear's sensitivity to loudness verses frequency. They conclusively demonstrated that human hearing acuity is essentially dependent upon loudness. The curves show the ear most sensitive to sounds in the 3 kHz to 4 kHz area. This means sounds above and below 3-4 kHz must be louder in order to be heard just as loud. For this reason, the Fletcher-Munson curves are referred to as "equal loudness contours." They represent a range of sensitivity from "barely heard," (0 dB SPL) all the way to "painfully loud" (120 dB SPL), usually plotted in 10 dB increments.

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    Flush (mounting)
    Mounting a speaker in such a way that the speaker and its Grill do not protrude above the surrounding surface. Usually, this means mounting it at the back of the baffle board (the board the speaker is mounted on).

    The flow of magnetic energy in a circuit. Flux density is the measure of the strength of the magnetic field typicaly used in speakers, and which governs its power handling capacity.

    The cylindrical portion of a speaker's voice coil section. A wire is wound around this cylinder to form a coil such that when current interacts with the magnetic field it produces a pumping motion that alternatively compresses and rarifies air, and creates the velocity for such air masses to reach our ears as sound.

    Free-Air Configuration
    This description usually indicates a speaker that, in the opinion of the manufacturer, is suitable for mounting in only a minimal enclosure, such as a baffle board that separates the back wave from the front.

    Free-Air Resonance (see Fs).

    Free sound field
    A sound field without acoustic boundaries or where the boundaries are so distant as to cause negligible reflections over the frequency range of audible sound. If the boundaries exist but completely absorb the sound then a virtual free field is created, thus anechoic chambers are used to accurately measure loudspeakers for their unique properties.

    1. The property or condition of occurring at frequent intervals. 2. Mathematics. Physics. The number of times a specified phenomenon occurs within a specified interval. In sound this simply refgers to the regular occurence of compression and rarification of air that we experience as sound.

    Frequency Modulation (FM)
    In radio broadcasting, a method of modulation in which the frequency of the carrier voltage is varied with the frequency of the modulation voltage (Also see Amplitude Modulation).

    Frequency Response
    The range of frequencies that a speaker will reproduce (lowest frequency to the highest). While the optimal normal is 20 - 20,000 Hz (Hertz), the range of human hearing for individuals is often much more restricted. A good full-range speaker system however, will reproduce as much of this range as possible in order to cover all variations. Individual Drivers are limited to reproducing only that part of the spectrum for which they were made, so their response will be limited, but still a necessary point to consider when designing a complete sound system.

    Fs or Free Air Resonance is the frequency at which a speaker naturally resonates, like a tuning fork. Sometimes known as ringing response.

    Full Logic Deck
    A cassette mechanism where the tape operations are carried out by logic circuit operated solenoids rather than soley mechanical methods.

    A device designed to provide protection for a given circuit or device by physically opening the circuit. Fuses are rated by their amperage and are designed to blow or open when the current being drawn through it exceeds its design rating. They can be fast or slow acting, depending on type.

    Fusible Link
    Designed to perform the same task as a fuse, but the resembles a wire. Fusible links are commonly used in power transformers, ignition switches and other high current circuits.

    F3 (measured in Hz)
    The frequency at which the acoustic power output from a system has fallen to one-half its reference value. Known as the systems 3dB down point. F3: determined by the frequency at which the output is 3dB lower than the level at 100Hz. This frequency was chosen because it is a typical crossover point. In the case of a Bandpass system, F3 is determined by the frequency at which the output is 3dB lower than the level at the middle of the pass band.


    An increase in volume or amplitude, usually measured in dB.

    Gas Plasma
    Gas plasma emitters are a type of Horn Driver wherein a plasma or ionized gas field is developed and then propelled between two electrostatic grids. The onrushing gas is then compacted or dispersed in conformity to the frequency and level of the high voltage input signal. This type of driver, while very effective, is also extremely expensive, and so has not been commercially successful.

    A machine that produces AC electricity from a rotating coil interaction within a magnetic field. In automotive applications, a rectifier is used to convert this output to DC. Also, an electronic device used for converting DC voltage into AC of a given frequency and wave shape. An amplifier is often a form of generator.

    Granulation noise
    A type of audible distortion resulting from quantization error in digital transmission modes.

    Graphic equalizer
    A multi-band variable equalizer using slide controls as the amplitude adjustable elements. Named for the positions of the sliders "graphically" illustrating the resulting frequency response of the equalizer. Only found on active (amplified)designs. Center frequency and bandwidth are fixed for each band.

    A barrier meant to prevent damage to the Driver that it covers, or that creates a more attractive appearance.

    A term that describes anything having an electrical potential of zero relative to other points in a circuit. Most


    Haas Effect
    Also known as precedence effect, describes the human psychoacoustic phenomena of correctly identifying the direction of a sound source heard in both ears but arriving at different times. Due to the head's geometry (two ears spaced apart, sometimes separated by a barrier) the direct sound from any source first enters the ear closest to the source, then the ear farthest away. The Haas Effect describes how humans localize a sound source based upon the first arriving sound, if the subsequent arrivals are between 25-35 milliseconds. If the later arrivals are longer than this, then two distinct sounds are heard. The Haas Effect applies even when the second arrival is louder than the first (even by levels as great as 10 dB.)

    Hard Dome (Tweeter)
    A characteristic of some Dome tweeters in which the dome is made of some light, hard metal such as neodymium, titanium, or some of the more rigid plastic compounds. The differences in reproduction between hard and soft dome tweeters, are distinctive, but very subtle. Pay close attention to how these sound before purchase.

    Harmonic Distortion
    A type of Distortion in which resonance or sympathetic ringing vibrations are added to the original sound to produce second and third harmonics of a fundamental tone in a way that was not present in the original signal. Choosing good Drivers and a well-made enclosure design is essential in overcoming this tendency in speakers.

    The universal name for a bundle or loom of wires that compose the wiring for a system.

    Hatchback (box or enclosure)
    An enclosure of such size and shape as to enable its efficient use in hatchback-style vehicles. Normally, these enclosures are somewhat deeper than standard angled enclosures and have either handles on the end panels or no handles at all.

    A term related to the dynamic range of amplifiers, used to express in dB, the level between the typical operating level and the maximum output level (onset of clipping). For example, a nominal +5 dBu system that clips at +25 dBu has 20 dB of headroom. Because the term depicts a pure ratio, there are no units or reference-level associated with headroom, only relative "dB." Therefore headroom expressed in dB accurately refers to both voltage and power. Which means the example above has both 20 dB of voltage headroom, and 20 dB of power headroom.

    Heat Dissipation
    The function of transfering heat away from a component into the air to prevent damage to the output section of an amplifier or the voice coil of a speaker.

    Heat Sink
    Parts of an amplifier, typically heavy metal "fins," and a section of the frame of the speaker used to conduct and radiate heat away from the ponit of electrical consumption, or motor assembly.

    The measurement of frequency. One hertz is equal to one cycle per second, or the complete cycle of an alternating (AC) waveform. Higher frequencies are measured in kilohertz, (thousands of cycles per second) Megahertz, (millions of cycles per second), etc.

    High Fidelity
    A method of sound reproduction that emphasizes the highest possible adherence to the exact character of the original sound. This is a principal that must be paramount in every stage of the recording, transportation, and re-creation of the signal to be fully operational. It is usually the listener's equipment wherein this objective is most seriously compromised.

    High Level Input
    An audio input configured to accept speaker level signals.

    High Power Output
    Speaker level outputs driven by an amplifier, typically at least 15 watts RMS per channel.

    High Pass
    An electronic filter of a type commonly incorporated in Crossover circuits that permits the passage of high frequencies while suppressing lower ones. The place in the frequency spectrum where this occurs is called the crossover point and is different for each set of Drivers being considered. The most basic form of such filter is a non-polarized capacitor. Typical values for such a unit would be in the range of 1 to 100 microfarads.

    High Voltage Switching Power Supply
    An amplifier's internal power supply that converts the vehicle's 12 volts to higher voltage for improved dynamic range and higher amp output power.

    A type of speaker system now principally used for high-frequency reproduction, but which is capable of full range sound in its largest format. As with those huge alpine horns, even the smallest transducer or diaphragm can produce the lowest sound if the horn is long enough and large enough at its business end. (see Compression Driver above)

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    Horn Tweeter
    A driver consisting of a relatively small emitter surmounted by a curvilinear or exponential horn. This is an effective system for radiating high frequencies in a variety of situations. The size and shape of the horn will usually dictate the pattern and use of the driver. Long horns with narrow apertures, tend to have the narrowest radiation pattern, and are very useful in large listening rooms, especially where highly directional effects, such as surround sound requires, are mandatory. Shallower versions have more general applications, especially in car stereo applications where a wider field of coverage is desired, along with a robust driver that can withstand severe environments. In such situations, a Piezo driven emitter (driver) is highly desirable for its ability to handle high-energy inputs on a variable basis. Horns can be driven by a number of different driver types: Dynamic ,(magnet and coil) Piezo, Electrostatic, Ribbon, and even Gas Plasma have been used effectively for this purpose.

    Hum components
    The residual artifact harmonics of the AC power supply. In the U.S. the use a 60-Hz system, places the most annoying 2nd and 3rd harmonics at 120 Hz and 180 Hz. For Europe, and other parts of the world using 50-Hz mains, these components fall at 100 Hz and 150Hz. To some extent, this is present with nearly all non automotive sound systems and is generally accounted as noise.

    Hyperbaric Resonator Impulse
    An audible event characterized by a sudden and often unexpected pressure wave emanating from a vent port with a driver whose energetic and propulsive energy transitions, are generated by a process involving the chemical modification of legumes. This phenomenon frequently produces olfactory irritation in associated groups in consequence. This event is also know as a Farsical Audio Report Transient.


    Imaging describes the extent to which an audio system reproduces the directional cues that enable the listener to locate the instruments and vocalists as they were positioned during recording and mixing (See also Soundstage below). Good imaging creates a listening experience that seems natural and lifelike. Since directional cues in sound come mainly in the higher frequencies, the key to attaining the best possible imaging is to have equal and unobstructed path lengths between the tweeters and the listener's ears. That's one of the reasons why matched component speakers, with their versatile tweeter placement, sound as good as they do.

    The totality measured in Ohms of all electrical opposition to current flow: resistance, reactance, capacitance, as well as all mechanical factors inhibiting the completion of energy transfer in a contained system. In practical terms, this means that most Drivers are assigned a certain nominal impedance based on their DC voice coil resistance and mechanical stiffness. For car audio this is usually 4 ohms; for home stereo, 8 ohms is the standard.

    Waves or vibrations with frequencies below that of audible sound (20 Hz.).

    Inductive Coupling
    Radiated noise that is transmitted through a magnetic field to surrounding lines. This frequently occurs in long runs owire where power and signal cables are in too close proximity. This is a frequent source of noise and interference.

    A transformer, or an electrical component in which impedance increases as the frequency of the AC decreases. Also known as coils. In audio, these are used in passive crossovers. Inductors are rated in Henrys.

    Infinite Baffle
    An infinite baffle speaker design is defined as an enclosure that contains a greater volume of air than the Vas requirement of the driver. An infinite baffle system can easily be applied to an automobile. This is accomplished by mounting the speakers on a board and using the trunk of the vehicle as the other walls of the enclosure. It is important that the enclosure be tightly sealed such that no air moves from the front to the back of the cone. Look for speakers where the Qts is greater than .6, and a Vas figure lower than the volume available, when selecting a woofer for an infinite baffle system.

    Institute of High Fidelity - the premier institution for high fidelity whose standards have come to be universally recognized in application to the operation and design of sound re-enforcement and reproduction equipment.

    Input Sensitivity
    is the SPL (sound pressure level) a speaker will produce given one watt of power as measured from one meter away given a typical input frequency (usually 1kHz unless otherwise noted on the speaker). Typical sensitivities for car audio speakers are around 90dB/Wm. Some subwoofers and piezo horns claim over 100dB/Wm. However, some manufacturers do not use true 1W tests, especially on low impedance subwoofers. Rather, they use a constant voltage test which produces more impressive sensitivity ratings.

    Input Voltage
    The power voltage provided to an amplifier. While most cars can be expect to reliably produce 12 volts, amplifiers are sometimes measured at higher voltages; up to 15 volts. In this way, higher power can be developed, albeit at the expense of longevity. It is a practice that allows higher power figures to be claimed.

    Insertion Loss
    The loss of voltage (or power), as measured in dB, resulting from placing a resistor (or some other power absorbing network or component) between a voltage or power source (amp) and its load impedance (speaker.) It is the ratio of the voltage (or power) absorbed in the load without the resistor (or network) to that when the network is inserted. For example, if the voltage across a load is 2 volts without a network and 1 volt with the network, then the insertion loss is stated as 6 dB.

    Intermodulation Distortion
    A species of Distortion that results when one set of frequencies is superimposed on, or is modified by, another to produce a third frequency not present in the original signal. Quantifies the distortion products of nonlinearities in the unit under test that causes complex waves to produce beat frequencies, i.e., sum and difference products not harmonically related to the fundamentals.

    A non-conductive protective covering for electrically active parts and wire that prevents short circuits and other unwanted interference.

    Inverted Dust Cap (see Dust Cover/Cap)

    Sometimes spelled Isobaric, this is an enclosure design in which two or more Drivers are coupled together by a sealed air mass to operate as a single driver. With proper sealing and design, very impressive results can be obtained from an unusually small box. A popular version of this simply consists of two woofers placed over each other in a 'clamshell' design. The downside consists of the fact that it does require at least twice the amplifier power as would be needed for a conventional speaker, in order to be operated successfully.

    ISO-DIN Mounting
    Refers to a receiver mounting system in which the headunit is mounted behind the dash panel with side brackets, employing factory installed trim panels.1

    Electrical or acoustical separation to prevent the spread of noise and the effect on the signal of unwanted elements produced by internal or external devices.


    A receptical for a plug used to interconnect electronic devices.

    A unit of energy equal to one watt per second.

    Jump, Jumper
    To provide a temporary circuit around a component or other circuit A device that anables this action


    A voice coil design in which multiple layers are used on a Kapton coated coil form to create the rotor element in the speaker driver's linear motor. This allows greater power handling, and cooler operation.

    A panel usually made of metal or plastic with numbered push-button switches (like a touch-tone telephone) designed to provide access to certain types of control functions. Security, CD changers, and cellular systems represent typical examples

    Kirchoff's Current Law (KCL)
    A law stating that the total current entering a point or junction in a circuit must equal the sum of the current leaving that point or junction.

    Kirchoff's Voltage Law (KVL)
    A law stating stating that the voltage supplied to a DC circuit must equal the sum of the voltage drops within the circuit .

    KHz (kilohertz)
    A frequency of one thousand (1,000) cycles per second.


    Liquid Crystal Display. Probably the most common way of showing visual information on non-computer electronic equipment.

    A low resistance (commonly 8 ohms) potentiometer used primarily to control the input delivered to a speaker. A remote site volume control.

    Le (Measured in millihenries, mH)
    The electrical inductance of a speaker’s voice coil.

    An electronic compressor with a fixed ratio of 10:1 or greater. The dynamic action effectively prevents the audio signal from becoming any larger than the threshold setting. For example, if the threshold is set for, say, +12 dBu and the input signal increases by 10 dB to +26 dB, the output only increases by 1 dB to +13 dBu, essentially remaining constant. Used primarily for preventing equipment overloads, thus reducing clipping distortion.

    Standard +4 dBu or -10 dBV audio levels. Used in communicating standard signals between processing devices, such as : receiver to equalizer, or equalizer to amplifier.

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    1. Referring to mechanical movement, the ability of the voice coil to move in and out in the air gap without moving side-to-side. Non-linear movement can damage the voice coil.
    2. Referring to woofer response, the ability to maintain power or movement without loss of drive force.
    3. Referring to enclosure port operation, the relationship bewteen the amount of air moving through the port vs. the amount of air moved by the cone. Non-linear response in a port can cause audible distortion.

    Linear phase response
    Any system which accurately preserves phase relationships between frequencies.

    The degree to which a given transducer or amplifier can produce an equal response within its specified range. This is usually measured in dB with +or - as small a number as possible indicating the least amount of variance from the desired flatness.

    Listening Position
    A feature which can optimize frequency response and imaging for a particular position in a vehicle through the use of signal delay.1

    The resistance or impedance to which energy is being supplied. In amplifiers, the speaker or speakers connected to the output of the amplifier.4

    The difference between potential energy output and actual energy output.

    The Sound Pressure Level of a standard sound which appears to be as loud as the unknown. Loudness level is measured in phons and equals the equivalent SPL in dB of the standard. [For example, a sound judged as loud as a 40 dB-SPL 1 kHz tone has a loudness level of 40 phons. Also, it takes 10 phons (an increase of 10 dB-SPL) to be judged twice as loud.]

    An electro-acoustic transducer that converts electrical audio signals at its input to audible sound waves at its output.

    Low Frequency
    Refers to radio frequencies within the 30-300 kHz band. In audio it usually refers to frequencies in the 40-160 Hz band.

    Low Pass Filter
    A network of components which attenuate all frequencies above a predetermined frequency selected by the designer. Frequencies below cut-off are passed without any effect.

    Low Q
    A low Q, or QTS, (reactance) woofer Driver is desirable for use in a vented enclosure.


    Magnet/Magnet Structure
    A combination of magnetic material and connected field concentrators that creates the magnetic field within which the voice coil interacts to produce sound. Magnetic materials have changed greatly over the years to produce much higher concentrations of magnetic fields (rated in gauss) with lighter and smaller volumes of material. In marketing speakers, a great deal of hype is applied to the question of magnet weight. But many of these claims should be treated with skepticism. With greater and greater concentrations of gauss fields being developed from ever lighter metallurgical materials, the only good measure of adequate power handling is the manufacturer's RMS Wattage rating. Hefty magnets may look impressive, but while capable,they are no longer an essential index to a speaker's power capacity.

    Magnet Boot
    A rubber or plastic cover for the magnet housing for protection or appearance, mostly the latter.

    Magnetic Flux Density
    The measurement of magnetic flux, in units of Gauss, inside the air gap in which a voice coil of a speaker operates.

    MAX (see Peak Power Handling)

    The word most commonly used to refer to a system's ability to retain specific information.

    Memo List
    A Custom File feature that allows the user to toggle through the discs, selection titles, or station call letters currently loaded without interrupting playback of the existing disc or station.

    Metal Tape EQ
    An equalization circuit that compensates for the unique frequency response characteristics of metal tape.

    1. A unit of atmospheric pressure equal to one millionth of a bar. 2. A place to consume the product of microbreweries.

    A multiple semiconductor IC device that can be dedicated or programmed to perform a variety of tasks in many different systems. These exist in virtually all consumer and commercial electronic devices of more than rudimentary functionality.

    Those frequencies roughly between 100 and 300 Hertz. (CPS)

    A Driver that is usually much smaller than a woofer, but with a surface area greater than the typical tweeter. It reproduces the mid frequency range from approximately 300 to 5000 Hertz. This optimum range can vary considerably from one driver to the next, thus giving the system designer more flexibility in choosing Crossover points for the other drivers.

    A unit of measurement of electric current equal to 1/1000th of an ampere. The milliampere is the most common unit used when measuring quiescent current drain in consumer audio electronics.

    At its simplest level, an audio processing device used to add (combine or sum) multiple inputs into one or two outputs, complete with level controls on all inputs. From here signal processing is added to each of the inputs and outputs until behemoth monsters with as many as 64 inputs are created -- at a cost of around 10-20 thousand dollars per input for fully digitized and automated boards.

    Mono (monaural)
    The operation of an amplifier in one channel for both input and output. Can refer to an amplifier with only one channel of amplification or operating in bridged mode. For low frequency amplification applications, it provides the better phase coherence and less distortion than stereo operation.

    MOSFET (Metal Oxide Semiconductor Field Effect Transistor)
    A type of large output transistor used in the final stages of many power amplifiers, and commonly found in most car and home amplifiers today.
    These field-effect transistors are controlled by voltage rather than current, like a bipolar transistor. MOSFETs have a significantly higher switching speed than bipolar transistors. They generate almost no loss (little heat generation), which lends the power supply fast response, excellent linearity, and high efficiency.
    Mosfet transistors are most often discrete devices, used with smaller driver transistors and other devices, to convert a small signal to a large one. They are highly stable and efficient, compared to the bipolar types that preceded them.

    MOSFET Power Supply
    A power supply that employs MOSFET transistors to convert DC to AC. Offers superior thermal stability and more accurate switching.

    Motor Structure
    The complete sound generator or transducer that converts incoming electrical signals to mechanical/acoustic energy or sound. In a dynamic Driver, this includes the magnet, its directive field concentrators or Pole Pieces, and the voice coil that interacts with them.

    Mounting Depth
    The amount of physical space required to mount a Driver without having any of its parts touch objects below. This is particularly relevant to car speakers where such mounting spaces may be sharply limited as to their ability to accommodate deep speakers with large magnets. Door panels are a typical example of where care must be taken in selecting speakers to be mounted. (see Mounting Ring, below)

    Mounting Ring
    Often used to describe the circular gasket seal incorporated into the edge of a speaker, traditionally the term "mounting ring" refers to a separate device placed between a Driver and the surface on which it is mounted, for the effect of raising the speaker so that larger and deeper speakers can be accommodated in limited spaces. (see Mounting Depth, above)

    A control found on receivers, some mixers, and certain signal processing units that silences (mutes) a signal path, or output.

    A common term used to describe a VOM. A multimeter usually has the ability to measure volts, ohms, and amperes or milliamperes.


    Near Field Sound.
    Typically, any point where the direct sound emission is measurably louder than the reflections of that sound. From a more accurate technical perspective, this is the point where the velocity of molecules emitted by the radiator is out of phase with the sound pressure wave. This is especially obvious when the listener is in close proximity to high frequency emissions.

    Negative feedback
    The dynamic comparison of a fraction of the output signal to the input signal at the input to an amplifier in such a way that the amplifier regulates it's output signal for maximal conformity to the input signal. Negative feedback is frequently used in designing opamp circuits and audio power amplifiers.

    Negative LCD
    A liquid crystal display employing a dark backfield with lit elements. This results in a primarily dark display, which improves cosmetic integration with a dark colored headunit.

    Neodymium Magnet
    A magnet material providing 7.5 times the magnetic strength of standard magnetic materials.

    Net Volume
    The amount of airspace that is enclosed within a speaker's enclosure. This does not include the airspace taken up by bracing, vents, or the speaker itself.

    Perceived sounds not in the original soundtrack. Such things as hiss, crackle, pops, hum, and buzz, are typical of the types of extraneous signals described as noise. Inherent noise in the electronic processing in any sytem is measured in decibels relative to the amplitude of the original signal.
    Sounds perceived as noise are heard in contrast to the sound that is the object of attention. Thus, a noise signal measured at 15 deciBels below the output of Tchaikovski's 1812 Overture finale would probably not even be heard; while a slight hiss at 55 dB below the level of a soft piano passage would be annoyingly obvious.

    Generally, any piece of equipment which generates ambient noise of more than 90 dB below the level of a typical audio signal is noise free as far as most human perception is concerned.

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    Noise floor
    Normally the lowest threshold of useful signal level (although sometimes audible signals below the noise floor may be recovered).

    Noise gate
    An expander with a fixed "infinite" downward expansion ratio. Used extensively for controlling unwanted noise, such as preventing "open" microphones and "hot" instrument pick-ups from introducing extraneous sounds into the system. When the incoming audio signal drops below the user set-point (the threshold point) the expander prevents any further output by reducing the gain to "zero." The actual gain reduction is typically on the order of -80 dB, thus once audio falls below the threshold, effectively the output level becomes the residual noise of the gate. Common terminology refers to the gate "opening" and "closing." Another popular application uses noise gates to enhance musical instrument sounds, especially percussion instruments. Judicious setting of a noise gate's attack (turn-on) and release (turn-off) times adds "punch," or "tightens" the percussive sound, making it more pronounced.

    Non-Delay Play
    A disc changer feature with significantly reduced silence between the time one disc is finished, and the next disc is loaded and cued.

    Nominal Impedance
    The minimum impedance a loudspeaker presents to an amplifier, directly related to the power the speaker can extract from the amplifier.

    Notch filter
    A special type of cut-only equalizer used to attenuate ( no boosting ) a narrow band of frequencies. Three controls: frequency, bandwidth and depth, determine the notch. Simplified units provide only a frequency control, with bandwidth and depth fixed internally.

    National Television System Committee. Refers to the standards used for video broadcast and playback signal parameters in the U.S. Japan and other countries. Alternative systems used in Europe and some Asian countries are PAL and SECAM.


    In audio, the interval between any two frequencies having a ratio of 2 to 1. One octave up from 100 Hz is 200 Hz, where one octave down from 100 Hz is 50 Hz. A harmonic is a doubling (2nd harmonic), tripling (3rd harmonic), quadrupling (4th Harmonic... etc) of a fundamental frequency. Musical instruments (with the exception of electronic synthesizers) do not create pure tones. The fundamental (main frequency) is combined with its harmonics at various levels to create the sonic signature, or timbre of that instrument.

    The measurement of electrical resistance and system impedance. It is a measure of the degree to which electrons are limited in both velocity and quantity in passing through a circuit. In Impedance measurements, this takes into account, the mechanical resistance inherent in the motion of transducers. The standard is usually 4 ohms for car audio and 8 ohms for home and commercial audio. Some specialty woofers may be rated at 16 ohms.

    Ohm's Law
    The mathematical relationship between voltage, current, and resistance. It is named after George Ohm, it's discoverer. Ohm's law states that current volume in a conductor is directly proportional to the voltage flow across it and inversely proportional to its resistance. In general, this means that more voltage will produce more current, if resistance stays the same, but higher resistance will cause current to decrease if voltage stays the same. In mathmatical terms, V = I x R, where V is voltage, I is current, and R is resistance. Ohm's law is a description of electron behavior upon which virtually all understanding of electronics is based.

    Literally, from all directions. In audio, microphones are said to be omnidirectional if they can detect sound with equal sensitivity from all directions. Speakers are omnidirectional if they produce sound pressure level that is the same without regard to the position of the listener vis a vis the axis of the driver or port; this tends to be the case with subwoofers and low frequency drivers. Low frequencies, in general, tend to be omni-directional, unlike high frequencies, where directionality increases with frequency.

    On Axis
    A listening experience which takes place with the ear precisely lined up with the central pressure axis of the emitter. Headphones are a normative example of this effect. Sitting directly in front of a speaker is another.

    Op amp
    (operational amplifier) An analog integrated circuit device having two opposite polarity inputs and one output; frequently used as a basic processing unit in the design of analog signal circuits.

    A device which produces an alternating current or pulsating current or voltage at varying frequencies, electronically.

    Output (Audio)
    The high level (speaker) or line level (RCA) signals sent from one system component to another, or the high level signal from an amplifier to the system speakers.

    A technique where each sample from a data converter is sampled more than once, i.e., oversampled. This multiplication of samples permits digital filtering of the signal, thus reducing the need for sharp analog filters to control unwanted frequencies created when sampling a signal of a frequency higher than half the sampling rate.

    Similar in concept to a harmonic. Overtones are sounds produced by an instrument (or sound source) that are higher in frequency than the fundamental frequency. They may or may not coincide with the frequencies of a harmonic series (harmonics), although they usually do. Harmonics are always musically related to a fundamental in that they are integer multiples of it. Overtones of a sound are often identical to its harmonics except the first overtone is considered the second harmonic because the first harmonic is the fundamental. Overtones are also sometimes called partials.


    Parallel Wiring
    A circuit in which two or more devices are connected to the same source of voltage, sharing a common positive and negative point, so that each device receives the full applied voltage.

    Parametric Equalizer
    A multi-band equalizer enabeling control of at least three essential "parameters" of the internal bandpass filter sections. These parameters being: amplitude, center frequency and bandwidth. This allows the user to not only control the amplitude of each band, but also to shift the center frequency and to widen or narrow the width or coverage of the affected section of the aural spectrum. Regulation is done by either rotary and slide controls. Other types of parametric equalizers exist which allow control of center frequency, but not bandwidth. For rotary control units, the most common term is quasi-parametric. For units with slide controls the popular term is paragraphic. The frequency control may be continuously variable or switch selectable in steps. Cut-only parametric equalizers (with adjustable bandwidth or not) are called notch equalizers, or band-reject equalizers.

    Passive Radiator
    Sometimes known as a "drone cone," these passive devices respond to internal pressure within the speaker and react to it to produce reinforcing emissions to extend the output of the lower frequencies below the resonance point of the active woofer. They may look like Drivers but they lack an active motor assembly.

    Passive Component
    In a crossover system, a non-powered component used to separate an audio signal into a specified frequency band before it goes to a particular amplifier or driver. A passive device usually incurs some loss (expressed in decibels) to a system. Typical such components include capacitors, coils, and resistors.

    Peak Power Handling (MAX)
    Peak power handling refers to the amount of power a speaker is estimated to handle during a brief high-intensity musical burst. Since this can vary with both frequency and amplitude, it is a much less accurate way to judge speaker durability and performance than RMS (see RMS).

    The amount of time required to complete a full single cycle of a sound wave.

    Permalloy Tape Head
    A cassette tape head constructed of permalloy, an alloy made primarily of nickel and iron, used for its superior high wear resistance and permeability, offering superior frequency response at a low cost.

    The relative timing of a sound wave that is measured in degrees from 0 to 360.

    Phase Cancellation
    Audio signals are complex phenomena expressed mathematically as phasors, or vectors. When two signals have the same exact time relationship to each other, they are said to be "in-phase;" if they do not, they are said to be "out-of-phase." If the energy of two out-of-phase signals are combined, they will, in fact, subtract from one another. This is called phase cancellation. Another type of phase cancellation can be seen when water waves interact. One wave's energy becomes stronger when two waves collide in-phase (summing) and becomes weaker when they collide out-of-phase. Air (barometric) fronts act in the same way

    Phase Delay
    A phase-shifted sine wave appears displaced in time from the input waveform. This displacement is called phase delay.

    Phase Linear
    Any audio system which accurately preserves phase relationships between frequencies, i.e., that exhibits pure delay.

    Phase Shift
    The fraction of a complete cycle elapsed as measured from a specified reference point and expressed as an angle. 2. Out of phase in an un-synchronized or un-correlated way.

    A unit of apparent loudness, equal in quantum to the intensity in decibels of a 1,000 Hz tone estimated to be as loud as the sound being measured.

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    Piezo (Tweeter)
    A tweeter whose motor is simply a crystal of Piezo material through which the signal current flows. The crystal lattice responds to this by bending in proportion to the Amplitude and frequency of the incoming signal. Because it is a high impedance device, it does not need a Crossover in line with the source. Piezo tweeters are very efficient Drivers and are relatively inexpensive. They come in a large variety of designs and radiators.

    Piezoelectric Driver
    This is among the most robust and least expensive alternative drivers for the high frequency reproduction. The material used in the Piezoelectric Driver is a piezoelectric polymer first developed in the early 1960's. This piezoelectric polymer is a plastic-like material that, unlike a crystal, can be made into thin sheets and fashioned into a great variety of shapes. Its transient and high frequency response is very good because the moving mass is negligible. The driver operates by bending the lattices in the crystalline structure of the piezoelectric polymer film. The Piezoelectric Driver is inappropriate for low frequency applications, as it is incapable of large air displacements. This high frequency transducer is very uniform in response from approximately 2 kHz to 20 kHz. It typically is used in many car stereo enclosures and other compact space environments.

    Pink Noise
    Pink noise is a random noise source characterized by a flat amplitude response per octave band of frequency, i.e., it has equal energy, or constant power, per octave. Pink noise is created by passing white noise through a filter having a 3 dB/octave roll-off rate. Due to this roll-off, pink noise sounds less bright and richer in low frequencies than white noise. Since pink noise has the same energy in each 1/3-octave band, it is the preferred sound source for many acoustical measurements in respect to the critical band concept of human hearing. The name comes from the filtering of white noise. White noise is analogous to white light in that it contains all audible frequencies distributed uniformly throughout the spectrum. Passing white light through a prism (a form of filter) breaks it down into a range of colors. Examination shows that red light is characterized by the longer wavelengths of light, i.e., light in the lower frequency region. Similarly, pink noise has higher energy in the low frequencies, hence the term, pink.

    Polar response
    A plot of the Amplitude measurement of a speaker's output at a given frequency relative to an off-axis angle. In other words, the difference that exists between how a speaker sounds when being heard directly in front, compared to how it sounds while standing off to one side. (See Dispersion)

    Pole Piece
    The ends or "Poles" of a magnet from which the magnetic lines of force, measured in Gauss, are at the greatest strength. In a typical speaker, this will be at the gap within which the voice coil is located. (see Bumped & Vented)

    A polymer based plastic material offering superior resistance against resonance.

    A plastic based material used primarily for speaker cones due to its rigidity, damping and resistance against harsh environmental conditions.

    An opening, usually a tube, in an enclosure, through which sound is permitted to pass.

    Port Diameter
    The measurement across the port opening. Measured as internal diameter (not outer diameter .

    Port Length
    The measurement of the length of the port tube.

    Ported (enclosure)
    Any enclosure design with ports. In such designs the internal pressure wave is processed to be used either solely, or in conjunction with the woofer front wave in order to produce sound. A port can be a simple opening, a tube or a Passive Radiator.

    A three-terminal variable resistor. Two terminals connect to the ends of a flat resistor, while the third terminal is attached to a moveable contact that interfaces with the resistive element. The moveable terminal, or slider, is capable of being positioned from one end of the element to the other. There are many physical types, with the rotary design being the most common, followed by linear slider used in graphic equalizers, for example. Often used as voltage dividers in electronic circuits, the input voltage is applied to the top of the resistive element, while the other end is tied to ground or a common reference and the output is taken from the slider. When the slider is positioned to the top extreme, the output equals the input less of course, the effect of the resistor, moving it to the bottom extreme gives an output of zero volts; and every possible level between is available as the slider is moved from one end to the other. The most commonly encountered application of this arrangement to control the volume of an audio device. In this way the electrical potential is varied, hence, a potentionmeter. The rate at which the voltage changes as the slider is moved is controlled by the taper of the pot. The taper defines the amount of resistive change as a function of travel. Several popular examples are listed below:
    audio taper (aka A-taper): Usually 15% resistance at the 50% rotation point .
    linear taper (aka B-taper): Always 50% resistance at the 50% travel point
    log taper: Often used an an audio taper since its 50% rotation point has 10% resistance
    MN taper (" balance control") Special taper developed for home stereo. Consists of two sections (one for each channel) operating opposite each other. Exactly one-half of each section is a zero resistance surface (i.e., solid-copper or equivalent), the next 50% of travel is linear taper. Therefore for one channel rotating the slider through the first 50% of travel does not change the level at all, while the other channel is reduced from full to zero, and vice-versa, with the middle position (usually featuring a center-detent) always passing full signal to each channel.

    a. The product of applied voltage (potential difference) and current in a direct-current circuit (or the voltage squared divided by the resistance, or the current squared times the resistance). b. The product of the effective values of the voltage and current with the cosine of the phase angle (between current and voltage) in an alternating-current circuit. c.Power The amount of energy (in joules) that a device delivers or consumes divided by the time (in seconds) that the device is operating. See: apparent power and rms power.

    Power factor
    The ratio of the total power in watts (resistive load) to the total apparent power in voltamperes (VA) (reactive load). The difference between watts and VA is due to reactive load impedance. Apparent power equals watts only for a purely resistive load (i.e., zero degrees phase shift between the applied voltage and the resultant current). Power factor is best thought of intuitively as the multiplier (ranging between 0 and 1) that you must use to obtain the real power from the apparent power. For example if the rms voltage and current of a circuit is measured and multiplied together, the apparent power is obtained, but this value must be multiplied by the power factor to obtain the real power. If the load is purely resistive then the phase difference between the voltage and current will be zero and the power factor will be one, and the apparent power will equal the true power -- but only for a resistive load. For a reactive load (any load with inductive and/or capacitive reactance, i.e., any real world load) there will be a phase difference between the voltage and the current due to the phase delay introduced by the reactive elements. Simply put, since the maximum voltage and current do not occur at the same instant of time the amount of power developed is less than the measured rms voltage and current multiplied together.

    Power Handling (continuous or RMS)
    A rating of a Driver's ability in optimum conditions to handle a specified amount of audio power (electrical current power) on a constant basis, without damage. This is generally considered to be a conservative and reliable figure to use in judging what types of amplifier power will be most successful with a particular speaker design.

    A circuit unit which takes a small signal and amplifies it sufficiently to be fed into the power amplifier for further amplification. A pre-amp includes all of the controls for regulating tone, volume, and channel balance.2

    Preamp Output
    Typically found on headunits, a preamp output provides low level, high quality audio signal for use with external amplifiers.

    Precedence Effect
    Also known as the Haas effect, this phenomenon identifies the tendency for the ear to attribute all perceived sound to the nearest emitter, even if a more distant speaker is actually louder. Thus, drums that yield 90 percent or more of their energy in the non-directional lower frequencies are perceived as located in the space created by the tiny amount of higher frequency overtones. It is also for this reason that sounds from the rear speakers of a surround system are delayed by 10 to 30 milliseconds, so that they can be experienced as coming from the rear direction.

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    A collection of system settings stored in a memory that is virtually instantly recallable, typically at the touch of a button.

    Program Bank
    A Custom File feature that allows the user to flag the tracks on a disc, indicating whether they should be played or skipped.

    Program Play
    A Custom File feature that allows the user to define a sequence of 12 tracks, in a specific order, for customized playback. Up to two banks of 12 track sequences can be recalled, for up to 24 tracks total.

    The scientific study of the relationship between human hearing and its stimulus; in other words, how we hear.

    Like "hitting hard," a subjective colloquial term that describes the snap or deep impact of the low end response of an audio system


    The ratio of reactance to resistance in a series circuit, or the ratio of resistance to reactance in a parallel circuit.

    The Q of a speaker driver at its free air resonance considering only its electrical losses.

    The Q of a speaker driver at its free air resonance considering only its mechanical losses

    The total Q or resistance of a woofer and sealed enclosure at the system’s resonance frequency, considering all resistive losses. A Qtc of .7 has smoothest response and the lowest resonant frequency response. A Qtc of above 1.1 should only be used by those who prefer a "boomy" response.

    The total resistance in a series or parallel circuit. This takes into account all Driver resistances, both electrical and mechanical.

    Quick Release (terminal)
    A means for securing a wire conductor to a terminal connector that permits easy attachment and removal. In the usual form, this will involve a spring-loaded clip, which needs only to be pressed to either secure or detach a cable end.

    The process of converting, or digitizing, the almost infinitely variable amplitude of an analog waveform to one of a finite series of discrete levels. Performed by the A/D converter.

    Quantization error
    Error resulting from quantizing an analog waveform to a discrete level. In general the longer the word length, the less the error.

    A type of equalizer. A quasi-parametric (also known as "semi-parametric") EQ will allow control over the frequency and gain of each band of equalization, but not the number of frequencies controlled (bandwidth). The midrange EQs on mixing consoles are often quasi-parametric. More flexible in some ways than a graphic EQ, a quasi-parametric EQ does not offer the full range of adjustment found in a fully parametric design.

    Quiescent Current
    The term given to describe the amount of current consumed by a circuit when it is not performing any work (sometimes referred to as standby current).


    Radio Data System (RDS)
    RDS stands for Radio Data System. RDS tuners can automatically tune in stations according to the types of music (or talk) they broadcast. RDS also enables a receiver to display text messages and even graphics (usually call letters and format information) that many FM stations include on a subcarrier signal within their normal broadcast signal. Some RDS equipped tuners can even override with traffic alerts or emergency broadcasts, during playback of other media - CD MD, or cassette. There are other useful features too, many of which are offered by the growing number of RDS stations

    Radio Frequency (RF)
    An alternating current or voltage with a frequency (or carrier wave) above about 100kHz. It's called radio frequency because these frequencies have a capacity to be radiated as electromagnetic waves by radio ( and television) stations.

    Random Play
    Also known as shuffle play. In CD players and changers, this function randomizes the order of selections during playback. Some CD players offer a "Random Play with Delete" feature that prevents a piece from being repeated once it has been played.

    Random Code Encryption (or Varicode2 Transmitting System)
    In auto security systems, these terms describe anti-code grabbing technology, a feature which prevents malicious persons who use a special receiver to intercept remote control codes, from using it to defeat the alarm.

    Range (Audio)
    Usually described as frequency range, this is a system's frequency transmission limits, beyond which the frequency is attenuated below a specified tolerance. Also, the frequency band or bands within which a receiver or component is designed to operate.

    In sound waves, the opposite of compression. An area of decreased air pressure caused by a sound wave. In a graphical depiction of a cyclical waveform rarefaction occurs when the wave is in the bottom segment. Sound is simply the alternating compression and rarefaction of air at varying and often overlapping frequencies, within a range to which humans are sensitive.

    The inherent Direct Current resistance of a speaker's voice coil.

    In Ac circuits, whether passive or active, a form of frequency dependent resistance produced by inductors. Such an inductive loading will allow all dc current to pass without change, but will attenuate various, mostly higher frequencies, depending on the nature of the coil.

    Remote Control
    For remote-compatible devices, wired or infrared wireless remotes are either included with a receiver or CD player, or available as accessories. This enables the unit to be operated from the back seat or even outside the parked car.

    Remote Power-on Lead for Amplifiers
    This is a device that controls the power applied to operate the amplifier. It is essentially a relay circuit that is activated when a 12 volt potential is applied to the lead. This is most frequently applied by a connection to the car stereo receiver (head end) power antenna lead. When the radio is turned on, a 12 volt potential appears at the turn on lead and causes the motorized antenna to extend, and will also turn on the amplifier.

    Most all conductors of electrons exhibit a property called resistance. Resistance impedes the flow of current. It is measured in units called Ohms. With a water hose, resistance could be regarded as friction between the water and the hose. A larger hose would create less friction and have a lower resistance than a smaller hose. In electrical circuits, small round cylinders with wires on either end are called resistors. These typically reduce the flow of electrons to serve the specific requirements of the circuit elements, such as amplification or switching functions.

    The tendency for a mechanical or electrical systems to vibrate or resonate sympathetically at a certain frequency when stimulated by external energy. Every element and material has a particular natural resonance point. The job of the speaker designer is to minimize these output peaks whenever they appear so that a smooth response is created.

    Resonant Frequency
    The frequency at which a speaker cone vibrates with the least inertia. The point on the spectrum at which it has the greatest amplitude relative to all other applied frequencies.

    Reverberant Field
    The sound field that exists when the reflected sound at a listening position predominates over the direct sound from the source. This contrasts with near field effects. Layout, reflectivity and spatial parameters will strongly influence the creation of this situation.

    RF Modulator
    A device that converts a signal (typically audio and/or video) into a radio frequency. This can be received by a tuner and converted to perceptible information

    .Ribbon Driver
    The ribbon tweeter driver is a very thin corrugated aluminum "voice coil" hanging freely like a streamer in a side-by-side magnetic field. A ribbon is actually a type of dynamic driver, in which the voice coil is in the form of a flat, ribbon-shaped conductor which, positioned between opposite magnetic fields, actually becomes the diaphragm itself. The ribbon is free of the stretched film resonance's and obstructing magnets of the planar-magnetic, so it offers outstanding pulse response, uniform drive, and a good approximation of a line source, but the efficiency and impedance are both phenomenally low and the base technology is not usable as a woofer due to the small area. Most practical ribbons either use a step-down transformer or ask the amplifier to drive a ˝ ohm load (not a practical solution for most).

    The ribbon cannot be used to produce low frequencies. To create a moving element large enough to generate frequencies lower than a few hundred Hertz would mean moving opposing magnetic poles so far apart that they no longer exert a sufficient magnetic field over the entire area of the ribbon. But, a ribbon offers very precise treble around, superior to dynamics or electrostatics.

    In many ways, a ribbon driver can be an excellent performer: the moving element (the ribbon itself) is extremely light, allowing good speed and transient performance as well as freedom from coloration. They are however, expensive, and hard to find.

    The tendency for any vibrating surface to continue to produce the same frequency. This is limited by the decay time over which the inertia of other forces act to repress the motion. In acoustics, this tendency is known as reverberance. In human physiology, a condition called tinitus causes the sensation of ringing, which is actually a nerve disorder rather than a problem with the ear's mechanism.

    Ripple (Amplifier)
    A train of pulses that occurs when AC is changed to DC via a rectifier. These pulses are left on the DC if not filtered and regulated properly, or if too much current is being drawn.

    Ripple (Speaker)
    The maximum deviation from flat response, measured in decibels-it indicates the port's effect on woofer output.

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    Root Mean Square is a formula that provides a reasonably accurate means of measuring and comparing continuous AC power. The use of this measure is preferred when matching system components, like amplifiers and receivers. (See Power Handling)

    Roll Off
    A graduated reduction in the strength of audio output above and below certain specified frequencies. (See Crossover)

    Roof-Mount Antenna
    A permanently-installed antenna located in the center of a vehicle's roof.

    Room Response
    The effectiveness of any speaker system is a function of the room or environment in which it is played. The coupling of the speaker to the room or listening space is a function that is as critical as that between the woofer and the enclosure. When in doubt, experiment! This is the only practical method of achieving the optimal response form speakers in nearly any situation. Of course, computer modeling based on real time measurements could be substituted, albeit quite expensively.


    SACD (Super Audio Compact Disc)
    SACD is one of two main emerging new standards for high-resolution audio on compact discs. The other is DVD-Audio. It was developed by Sony and is based on a licensed technology called Direct Stream Digital, which was developed by Sony and Phillips and is theoretically capable of sample rates up to 2.8 MHz. The SACD format allows for playback of multi-channel audio and a bandwidth of 100 kHz at over 120 dB dynamic range while retaining compatibility with existing compact disc technology. There are several subformats in the works (single layer, dual layer, etc.) that are optimized for different tasks, but Sony claims that all SACD discs have fully uncompromised audio quality. That is, no data compression, and no computer generated surround mixes from stereo data or vice versa. The potential success of this format in the mainstream is currently under scrutiny amidst other developments such as DVD Audio, but there are a number of titles available on the Sony label with promised support from other record labels.

    Scan tuning
    In FM receivers, Preset Scan automatically plays a brief sample of what's on each of the preset stations. Station Scan samples each strong station regardless of whether it has been preset. Seek tuning moves to the next strong station and stops there — the "Seek" button must be manually initiated again to repeat the process.

    Screw Type (terminal)
    The most secure method of interconnecting the wire from the amplifier to a speaker. In its best realization, the terminal has a post with a hole drilled through it at the base, through which the incoming conductor is placed. A cap is then screwed down from the top of the terminal, compressing the wire below.

    Sd (a Theile Small parameter)
    Effective piston radiating area of a subwoofer driver in square meters.

    Sealed (enclosure)
    Sometimes known as an Acoustic suspension type, the sealed enclosure is a simple design in which each woofer is mounted in a sealed, airtight box or compartment with a specific internal volume for precisely the woofer being used. The air contained within the box or compartment then acts as a spring that allows more control over the speaker's behavior. Great care must be taken in design, as too small a box will sound "boomy," while too large a box may have hardly any bass at all. This should be remembered when replacing a woofer in such an enclosure. Best results can be expected when using woofers with a QTS between .30 to .90. These speakers offer good control, low Distortion and high power handling.

    The frequency attenuation that occurs at a rate of 12 dB per octave.

    Tuner specification which defines the tuner's ability to reject adjacent station interference.

    Sensitivity (Efficiency)
    The rating of a loudspeaker that indicates the level of a sound intensity that the speaker produces (in dB) at a distance of one meter when it receives one watt of input power.The Efficiency or Sensitivity rating indicates how effectively a speaker converts electrical power from the amplifier into sound pressure. This is frequently related to larger magnet sizes, larger voice coil diameters, and more compliant suspensions. Optimized enclosures are essential in achieving maximum sensitivity, overall. The higher the Decibel number, the more efficient the speaker and the louder it will play with the same input power. While usually more expensive, an efficient speaker helps maximize the potential of the available power.
    Also - The relative sensitivity to the reception of RF signals in a tuner measured in dBf. The lower the number the better. Normal is now 10 to 14 dBf.

    Separates or Matched Components
    A typical separates system includes a separate woofer, tweeter, and external Crossover, all of which are designed to work smoothly with one another. Generally, these components are made of better materials than two-and three-way Drivers. Separate woofers may be easier to mount in tight places because tweeter protrusion is not a factor. Separate tweeters allow positioning for optimum imaging. Given adequate power, separates can deliver excellent dynamics and detail. Separates are often a superior speaker design choice for many installations.

    Short Circuit
    The condition that occurs when a circuit path is created between the positive and negative poles of a battery, power supply, or circuit. A short circuit will bypass any resistance such as working componenets in a circuit, and cause it not to operate.

    Shuffle Play
    A feature which employs random selection from available tracks.

    Signal To Noise Ratio
    A measurement of noise level in a device compared to the level of the signal. Higher numbers signify a greater difference, which is better. In technical terms, it is the ratio, expressed in dB, of signal power at a reference point in a circuit, to the noise information that would exist if the signal were removed (the noise floor). The maximum signal to noise ratio (equivalent to dynamic range) of a given piece of equipment can be seen as a measure of functional fidelity. This ratio is how much absolute noise it produces, compared to the highest signal voltage it can pass without distortion.

    Silk Dome (tweeters)
    Dome tweeters in which the dome is composed of a treated soft silk like material. This is a design that is much less susceptible to mechanical deformation, and yet yields a fairly smooth response over the extent of its range.

    Slew Rate
    Slew rate measures the ability of a piece of audio equipment to accurately reproduce fast changes in amplitude. Measured in volts per microsecond, this spec is most commonly associated with amplifiers, but can bet applied to most types of equipment. In amplifiers, a low slew rate softens the definition of a signal, blurring transients and sounding "mushy." Slew rate is most critical in high frequencies reproduction where rapid changes in amplitude are most pronounced. An amplifier with a higher slew rate is often subjectively rated as tighter and more dynamic.

    The rate of change that a frequency response curve displays, normally stated in dB per Octave. Among other things, Slope can relate to Roll Off rates in Crossover action, low-end roll off and roll on rates and other forms of increasing or decreasing response.

    A type of physical kinetic energy called acoustical energy that falls within the portion of the spectrum to which humans are sensitive.

    Sound Discriminator
    A device designed to evaluate, and discriminate between the sounds that may be heard within the interior of a vehicle, and then trigger the security system should the sound fit within the parameters of what the sensor is designed to react.

    Sound Field
    The totality of the sound presented by the audio system. This includes the sound as it was recorded, mixed, transported, reproduced, and finally heard by the listener.

    The position (front/back and high/low) that music or sound appears to be originating from, as well as the apparent depth of the stage. A car with speakers only in the front will likely have a forward soundstage, but may not have enough rear fill to make the music seem live. A car with both front and rear speakers may have anything from a forward to a rear soundstage, with an accompanying fill from the softer drivers depending on the relative power levels and the frequencies reproduced. The high/low position of the soundstage is generally only obvious in a car with a distinctly forward soundstage. The music may seem to be originating in the footwells, the dash, or out on the hood, depending on the car's design.

    Sound Power
    The total amount of acoustical energy produced by a sound source and measured in Joules per second. The degree to which this measurement is constant( or linear)with respect to frequency, is an index of the overall fidelity of the system.

    Sound Pressure Level (SPL)
    An acoustic measurement of sound energy. 1 dB SPL is the smallest increment in sound level to which the average human is sensitive. Theoretically, 0 dB SPL is the threshold of human hearing while approximately 120 dB is the threshold of pain.

    Individual vocal and instrumental "images" make up your stereo system's soundstage. The degree to which particular sounds can be localized in space is an index to the quality of the imaging. The better the soundstage, the greater the sense of its definite width, depth and height. (See also Imaging above)

    Sound Waves
    Fluctuating waves of barometric pressure that travel through a physical medium such as air. An acoustic wave consists of a traveling vibration of alternate compressions and rarefactions, whereby sound is transmitted through air or other media.

    Source Impedance
    A parameter of an audio component referring to the output impedance. A low output impedence .5 to 4 ohms, is preferred for automotive applications.

  14. #14
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    The rear suspension element on the cone of a loudspeaker. All the moving parts of the speaker are suspended by the spider in the rear and the Surround in the front. The spider is so named because of its resemblance to an arachnid, especially in the way in which flexion is obtained in the design of the concentric pleats that allow back and forth motion. (SeeSurround)

    SPL (see Sound Pressure Level above)

    Stamped (Basket)
    The frame of a loudspeaker which has been stamp pressed to achieve its shape. It is used as a base to mount all the other elements of the driver. With a frame of adequate thickness and strength, this arrangement should perform well for the life of the speaker. (See Cast Frame,)

    Standing Wave
    A phenomenon where a sound is reflected between two parallel surfaces, such that certain sounds are made more intense and others diminished in given parts of a listening environment. Technically they are created by room modes, which are modes of vibration of air in the room. The sound waves interfere with one another to produce a series of places where the sound pressure level (SPL) at some frequencies is high, and another series of places where they are low. The places are sometimes called peaks and nodes. A standing wave exists in a room where a frequency is such that the distance between any two surfaces is equal to one half of its wavelength. For a given distance there will be many frequencies that will generate standing waves, each a multiple of the fundamental frequency whose wavelength is related to the dimension in question. Standing waves are always detrimental to the acoustics of a room, but can be avoided by careful room design, or minimized by absorbing certain frequencies where they build up, which is usually along walls or in corners.

    The distance that the speaker cone or voice coil can travel in both directions.

    Studio Monitors
    Speakers used in recording studios for playback and mixing of source recordings. While these are commonly thought of as extremely highly developed speakers, it is often true that some home oriented speakers may offer better performance. The term 'monitor' has become not so much a technical description, as an advertising ploy to sell expensive speakers. View such claims with skepticism. Favor a more analytical approach to an individual speaker's performance.

    Subwoofer (see Woofer)

    Subwoofer Preamp Outputs
    Individual number of RCA outputs that are coupled with a built-in low-pass crossover for connection to a dedicated subwoofer amplifier.

    Surface (mounting)
    A method of mounting speakers in which the external parts of the upper speaker protrude above the surface on which it is mounted.

    The surround is the flexible ring around the edge of the speaker cone. In conjunction with the inner suspension element called a Spider, it determines the overall impedance of the speaker. Pleated, treated cloth surrounds are usually stiffer and less compliant than their foam and rubber rolled edge cousins. A flexible suspension system in the speaker usually indicates greater efficiency. For some units, it is desirable to have suspensions that are pliable enough to let the woofer cone travel freely in and out. A technical specification for this characteristic in more expensive speakers, is XMS. The further the cone can travel and the more compliant it is, the stronger the bass can be in enclosures that take advantage of it. However, certain types of very good enclosures require a more limited, stiffer cone movement to develop their more controlled and High Fidelity response. Surrounds are usually made of cloth, foam or rubber. Rubber tends to last longest.

    Super Tweeter
    A Driver constructed to reproduce the highest possible frequencies from roughly 13 kHz to 25 kHz. While most standard Tweeters can do an excellent job right up to 16 or 20 kHz, these units deliver the most extreme parts of the upper range for those fortunate (or not) few who can actually hear them.

    Term used in reference to headphones. Supraaural phones rest on the ear, rather than enclosing the ear. Supraaural phones typically are lightweight, and because they do not seal around the ear, tend to not provide good isolation, but permit the listener a higher degree of awareness of external sounds.

    Sweet Spot
    The so-called "best" listening position in which the sound field is overlapped by the most direct radiations from all the speakers, and imaging is most convincingly achieved.


    Tape Equalization
    In tape decks, the best equalization response must be selected according to the type of tape — normal, chrome, or high-bias. In many decks, automatic sensors perform this function, in others, a switch must be set.

    Terminal Cup
    A plastic cabinet part that contains the terminal connectors that permits the wire from the amplifier to be connected to the speaker. Sometimes these parts contain the Crossover and protection circuitry as well.

    Total harmonic distortion is a measure of the how much a given audio device may distort a signal through the introduction of added harmonics or overtones. These figures are usually given as percentages. THD figures below approximately 1% are inaudible to most people. However, distortion is a cumulative phenomenon, so that if a receiver, equalizer, signal processor, crossover, and amplifier are all rated at "no greater than 1%THD", together, they could produce 5%THD, which may well be noticeable in the perceived sound.

    Theile/Small Parameters
    The work of Neville Theile and Richard Small is considered to have the most impact on the loudspeaker design field. They discovered a method that could predict the frequency response performance, and other characteristics of a loudspeaker system, based on its physical parameters.

    Three-way (car speaker)
    Three-way or triaxial speakers take the separate woofer and tweeter from a two-way design and add a dedicated midrange Driver for enhanced warmth and texture. The extra high-frequency energy also boosts overall Sensitivity.

    THX is a set of standards, components and systems are designed to meet in order to comply with the requirements of high quality film sound reproduction. First developed for Lucasfilm by Tomlinson Holmann, with input from George Lucas himself, THX was intended to define a minimum standard of equipment and quality control that theaters would need to meet in order to become 'certified' as THX approved. The idea was to raise the overall quality and consistency of audio in movie theaters. Lucasfilm had the clout to make such a certification mean enough from a marketing point of view, that theaters wanted to support it and be certified. Subsequently, it has been adopted as a standard in hi-fi equipment with many manufacturers licensing and producing certified THX components for home theater systems.

    TOC (Table Of Contents)
    The digital subcode information that identifies a disc, indicates the number of tracks, the starting and ending points of these tracks, and the total running time of the disc. When included, CD Text information is stored in the TOC.

    Toroidal Coil
    An inductor or transformer whose core consists of a concentrically wound ribbon of magnetic material. Also used to filter noise on a DC supply line.

    The path of conductive material, usually copper, that conveys voltage or current from one point to another on a printed circuit board. Traces add a slight resistance to the circuit.

    Synonym for Driver, speaker, or any electrical device that converts one type of energy into another. A microphone is a transducer that converts sound to electrical signals. A speaker reverses the process.

    An electrical inductive device that can be used to provide circuitry isolation, signal coupling, impedance matching, or voltage step-up.

    A non-repeating sound (such as percussion in music) or an abrupt change of voltage. How a speaker handles transients is a good indicator of its performance.

    An active (commonly three terminal) solid-state device in which a larger output current is obtained by small changes in the input current. Transistors comprise the greater number of active elements within ic's and microprocessors

    Travel Presets or Tuning Memory
    With this feature the receiver automatically loads it's presets with the strongest available signals. It makes finding stations easier when driving through unfamiliar territory. It also makes loading presets easier when the receiver is first installed, or any time the battery is discharged, or gets disconnected, which often cancels the tuner's preset memory.

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    Tube (enclosure)
    A type of woofer enclosure consisting of a long tube with a woofer at one end, and a port or Passive Radiator at the other. A good low-end reproducer, this design is very compact and generally used in car stereo.

    Tunable (port)
    A port tube that can be adjusted in length to provide for optimizing, experimentally, the measured low-end response when a speaker enclosure has not been designed for the woofer Driver installed in it.

    Tuned (port)
    A port opening, radiator, or tube whose size is precisely specified by the overall design of the enclosure and woofer.

    Highs are reproduced by the tweeter, a small speaker mounted inside the woofer cones of multidriver 2 and 3 way car speakers and separately in other systems. Cone tweeters are efficient and the most economical. Dome tweeters - the type found in most home speakers - have a wider angle of dispersion and more accurate. Some domes are made of metals like neodymium or titanium that yield extended high frequency response. Others are made of Mylar, or a fine cloth like silk and produce a smoother if not as extended response. Some are made from a combination of materials.

    "Two Ohm Stable"
    An X-ohm stable amplifier is an amp which is able to continuously power a load of X ohms per channel without encountering difficulties such as overheating or distrotion. Almost all car amplifiers are at least four ohm stable. Some are two ohm stable, which means that you could run a pair of four ohm speakers in parallel, or a single 2 ohm driver on each channel of the amplifier, and each channel of the amp would "see" two ohms. Some amps are referred to as high-current, which is a buzzword which indicates that the amp is able to deliver very large (relatively) amounts of current, which usually means that it is stable at very low load impedances, such as 1/4 or 1/2 of an ohm. Note that the minimum load rating (such as "two ohm stable") is a stereo (per channel) rating. In bridged mode, the total stability is the sum of the individual channels' stability

    Two-way (car speaker)
    Music's high frequencies are reproduced accurately by two-way, or coaxial, designs. These speakers use a separate tweeter to deliver high frequency reproduction that surpasses that of dual-cone "extended range" models with whizzer cones. This tweeter, usually a cone or a Dome, is either on a post or bridge inside the woofer.


    Having frequencies above the range of human hearing, commonly considered to be 20 kHz. Not to be confused with "supersonic," which means faster than the speed of sound. Ultrasonic frequencies in the signal path can sometimes cause harmonic distortion in audio components that are in the human hearing range and quite audible.

    Unfused Wire
    Any section of wire between the power supply and a load that does not include the protection of a fuse or circuit breaker.

    In music, unison is used to describe an identity of pitch. When two or more tones are sounding at the same frequency or pitch, they are said to be in unison with one another.

    Unity Gain
    A device or setting which does not change signal level, neither amplifying nor attenuating the signal, is said to be at "unity gain." Many processors are set up for unity gain; that is, they can be plugged into a system without changing its overall levels. In practice, unity gain is often a desired setting for maintaining gain staging, and for optimizing operating levels and signal to noise ratios.

    The tendency of an enclosure to produce no spring or pressure on the woofer. Unloading produces an uncontrollable over-excursion of the woofer cone (it vibrates out of control); the speaker will exhibit inadequate power handling at lower frequencies.

    Used Equipment
    Purchasing used equipment must be done with great care, especially in the case of speakers. An inspection of a speaker's voice coil would certainly reveal if it had been severly burned by exposure to clipping distortion. Unfortunately this could only be done by effectively destroying the speaker; obviously, not very practical. Observe if you can, what music the owner prefers, and how it is listened to. If speakers are consistently played with the amplifier volume set at more than half its range, on loud, bass-heavy passages, it might be wise to consider the destructive cumulative effects of clipping distortion and other such stress.

    The same caution applies little less rigorously to amplifiers, but not at all to signal source equipment (CD's, receivers, and Cassettes, etc.) and preamps, processors, etc. which are relatively impervious to high amplitude signals.


    Variable LP/HP Filter
    Crossover components which provide adjustable cut-off frequencies, and levels.

    Volume Acoustic Suspension. A volume of air in an enclosure that has the same resistance characteristic in acoustic terms as the speaker's suspension in mechanical terms. This is a factor taken into account when designing enclosures. It specifies the optimum internal volume of the enclosure.

    A measurement in liters or cubic feet of the volume of air that is equal to the compliance of the speaker's total suspension.

    Vented (enclosure)
    A type of speaker system also known as Tuned, Tuned Port, Ported, or Bass Reflex. They are basically Acoustic Suspension enclosures with the addition of a port or opening with a specific length. This allows a portion of the lower range to be coupled to the front wave produced by the woofer, in order to enhance the low frequency response. The portion of the range below the tuned point (Fb) is essentially a Free Air Driver that subjects the unloaded woofer to the possibility of severe, even catastrophic damage if the energy below this point is highly amplified. The best results for a vented speaker come when using woofers with a QTS in the range of .10 to .40.

    Vented (speaker - see Bumped & Vented)

    Voice Coil
    The voice coil is the coil of wire fixed to a cylinder at the apex of the loudspeaker cone that interacts with a magnetic field. With the help of other speaker components, the voice coil is the active transducer that converts electrical signals from the amplifier or receiver into mechanical energy, which we hear as sound. The voice coil cylinder is the part of the speaker around which the voice coil is wound. More advanced speakers offer a heat-resistant voice coil to prolong speaker life.

    Voltage is an electrical charge, or potential difference, between two points, one being of higher relative voltage than the other is. A 1.5-volt 'C' battery has 1.5 volts of difference between the positive and negative terminals, for example. The unit of voltage is called the "volt," named after Allesandro Volta. Voltage can be thought of metaphorically as a pressure, such as water pressure in plumbing, that is available to initiate action or work. It, however, cannot do any work until a circuit is complete so that current (measured in amperes) can flow.

    Voltage Drop
    The amount of energy consumed when a device offers resistance in its circuit. The voltage (E) set up across a resistance ® carrying a current (I). E=IR (Also see Volt).

    Volume is obviously the most common word used to specify the control of relative loudness of sounds. It also pertains to the function on many electronic devices that is used to control the loudness.
    Also - the measurment of the amount of space enclosed behind a speaker that functions as a resonance chamber.

    Volt-Ohm-Meter, sometimes called a Volt-Ohm-Milliammeter. A multimeter that measures voltage, ohms, and milliamperes.


    A measurement of power. In speakers, wattage is a term that indicates power-handling characteristics in dealing with electrical voltage inputs from the amplifier. RMS or continuous power handling is the only accurate basis for comparing the capabilities of Drivers. In determining the proper power input for a speaker, use this measure only. So-called Peak Power handling is often only the manufacturers best guess at the power dissipation point, beyond which the unit will fail.

    A single oscillation in matter (i.e., a sound wave). Waves move outward from a point of disturbance, propagate through a medium, and grow weaker as they travel farther. Wave motion is associated with mechanical vibration, sound, heat, light, etc

    The waveform of a signal is a depiction of its instantaneous voltages versus time. In audio, for example, we are always dealing with periodic waveforms that make up what we hear. These periodic waveforms can be plotted on a graph and will show up as some type of squiggly line. The graph chart rom left to right represents time and from top to bottom is the amplitude of the sound or voltage at those points in time. The familiar sine wave is an example of this.

    The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency.

    When laboratory measurements are taken of audio gear, the literal, "true" figures obtained often do not reflect the anomalies introduced by human perception. In these cases, the measurements obtained may be mathematically modified, or "weighted" to take into account the peculiarities of human hearing. A common example is "A-weighting", a curve applied to sound pressure levels to more accurately reflect our loudness perception. Other types of weighting compensate for the ear's frequency response, distortion tolerance etc.

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