AudioXtreme เพื่อคุณภาพเสียงในรถยนต์

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.
Acoustic Coupling	The interaction between two or more speakers stacked together in an audio system which may produce a sound different from (and often better than) the sound produced by the individual speakers.
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
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.
Acoustics	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.
Active	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
AC-3	(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.
AIFF	Short for Audio Interchange File Format, a file format for storing and transmitting sampled sound. It was developed by Apple Computer and is the standard audio format for Macintosh computers. Files are 8-bit mono or stereo and generally end with a .AIF or .IEF extension. Normal AIFF does not support data compression so files tend to be large, but another format called AIIF-Compressed (AIFF-C or AIFC) does support compression.
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
Amperes (A)	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".
Amplifier	A device, either a single stage or a large scale circuit with multiple 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.
Amplitude	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, a method 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).
AMS	Automatic Music Search. A feature that allows a CD or cassette mechanism to skip forward or backwards to another track.
Analog	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.
Anode	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.
Antenna	A device, such as a rod or wire, which picks up a received radio frequency signal or radiates a transmitted RF signal.
A periodic	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.
ATA	Automatic Tuner Activation. A feature that allows the tuner to be accessed while a tape deck is rewinding or fast forwarding.
ATRAC	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
Attenuate	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
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 volt amperes (VA) for reactive loads. The real power is usually less because of losses when the power factor is accounted.
Audio	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
Audiophile	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
AWG	Acronym for American Wire Gauge, a standard for measuring the diameter of wire commonly used in electrical circuits. The higher the AWG number, the smaller the thickness of the conductor. For power carrying, choose lower numbers; for signal only wires, choose a higher number.
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.
Baffle	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.
Bandwidth	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.
Basket	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.
Bass	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.
Bel	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.
Bi-Amplification	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.
BL	(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
BNC	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.
Boomy	Usually refers to excessively reverberant bass response, or a peak in the bass response of a recording, playback, or sound reinforcement system.
Box	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.
BTL	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.
BTM	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.
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.
Bumped	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
Buss or Bus	A signal-carrying conductor or electrical pathway designed to carry multiple signals. A mixing console auxiliary bus may carry signals derived from several channels on that console. The term is sometimes used to refer to a power distribution circuit, or "mains".
Butyl	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 pass band.
Cabin Gain	A low frequency boost normally obtained inside a vehicle interior when woofers are optimally in phase, and with the proper enclosures.
Canon/Cannon	Brand name of multipoint connector used for professional audio equipment. Also known as XLR connectors.
Capacitance	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, and micro, or Pico-farads for smaller units..
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. The amount of capacitance to be used is half (.5) farad per 500 watts of available RMS power. Capacitors are not used with amplifiers that supply less than 300 watts RMS in total.
Cardioids	"Heart" shaped pickup pattern characteristic of some microphones which reduces sensitivity to sounds from the sides and back.
CD Compact Disc	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 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.
Center Channel	in home theater, a signal sent to a speaker mounted in front of the listener, specially designed to enhance voices and sound effects associated with center stage action from a movie soundtrack. Sometimes used in car audio to help offset skewed stereo imaging due to seating positions in the automotive environment.
Channel	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.
Chord	A combination of two or more notes played simultaneously
Circuit Breaker	An electrical switch that automatically breaks a circuit if the current through it is higher than its rating. Once tripped it can be manually reset. Performs the same function as a fuse, but eliminates the need for replacement after activating.
Clipping	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.
CMS	referring to the compliance of the mechanical suspension of a speaker cone, consisting of the spider and surround.
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 connectors.
Coloration	A term used to describe levels of audio Distortion that cause serious departures from a true High Fidelity rendition of the original signal.
Compliance	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.
Compression (Audio)	The process of reducing the dynamic range of a given analog audio program by making the loud parts quieter and the quiet parts louder.
Compression (Data)	The process of packing digital data, such as computer files, more efficiently for the purpose of storage or transmission. Commonly referred to as 'stuffing' or 'zipping' a file.
Compression (Audio/Video Files)	A process of temporarily or permanently reducing audio data for more efficient storage or transmission. A temporary reduction in file size is called 'non-lossy' compression, and no information is lost. A permanent reduction in file size (such as with mp3 files) is called 'lossy' compression, and involves discarding (supposedly) unnecessary information which is irretrievably lost.
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.
Compressor	A type of dynamic range processor which reduces the gain of audio signals which are over an adjustable 'threshold' level, therefore reducing the dynamic range. Generally allows the operator control over threshold, ratio, attack and release times. Both analogue and digital types are available.
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.
Compression	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 ratification 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.
Concert Pitch	A standard for the tuning of musical instruments, internationally agreed in 1960, in which the note A above middle C has a frequency of 440 Hz.
Cone	The cone-shaped diaphragm of a speaker. This is directly attached to the voice coil motor which actions produces the pulsation's of air that the ear detects as sound. Also useful for holding ice cream.
Condenser Microphone	A mike that depends on an external power supply or internal battery to electro statically charge capacitor plates, one of which is subjected to sonic motion. Also called a 'Capacitor' microphone.
Conductor	Materials along which electrons will flow, making them suitable for use as connecting links in electrical circuits. Also, persons who guide symphony orchestras or streetcars.
Coulomb	An amount of electrical charge which contains 6.24 x 1018 of electrons. So there!
Counter firing	A method for reducing harmonic distortion at low frequencies that involves the use of a secondary coil in a woofer or mid bass driver to cancel non-fundamental wave elements not found in the original signal. The signal from the coil is used by the amplifier to refine it's damping control over the cone motion. This proprietary servo-feedback technology was originally developed by Velodyne in the early '90s.
Crossover	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.
Current	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.
Damper	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
Damping	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 switching 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.
DC	Direct Current.
Decay	The time of reduction of the level of a signal immediately after its cessation .
Decibel or dB	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.
Delay	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).
Detachable Face	Occasionally referred to as 'Removable Panel' or 'Theft Deterrent Faceplate', or some variation. This is a physical method for foiling receiver thieves. The idea is that you take just the front panel with the controls with you when you leave the car. A thief cannot buy a new face for a unit unless he has a receipt for it. Some manufacturers makes sets with rotating faces called Mask.
Diaphragm	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.
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.
Diffraction	a change in the direction and velocity of a wave front that is caused by the wave moving past an obstacle.
Diffuse	Widely spread out or scattered; not concentrated.
Diffuser	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.
DIN	Acronym for Deutsche Industries Norm (Deutsches Institute 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. Single DIN is the standard face size for receivers, and measures 7-3/8"wide by 2-1/4" high. DIN+1/2 measures 7-3/8"wide by 3-3/8"high. Double DIN measures 7-3/8"wide by 4-1/2" high.
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.
Dispersion	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.
Displacement	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 .
Distortion	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	The most common shared logo or feature between all brands is the Dolby labs' 'double D' symbol. Named after audio engineer, Ray Dolby, it represents a number of sound processing technologies that are incorp-orated in a diverse number of products since the early 1970's.
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.
Dress	The arrangement of signal leads and wiring for optimum circuit operation, cosmetic appeal, and protective routing.
Driver	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.
Dual-Cone	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.
Dub	A copy or the process of making a copy of a recording on another storage device.
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.
Dynamics	When used in music, refers to the varying degree of loudness and softness in a musical performance.
Earth	An electrical connection to the earth, which represents 0 volts or 'ground potential' by way of a metal or conductive rod.
Easter egg	A surprise "extra" coded into DVD's, computer programs or web pages that is accessed by an undocumented keystroke combination or hidden link.
EBP	Efficiency Bandwidth Product. A parameter that helps determine the suitability of a driver for a sealed or ported enclosure. An EBP of less than 50 indicates the driver should be used in a sealed box, 50 - 90 indicates flexible design options including bass reflex, over 90 indicates the need for a ported enclosure. EBP = Fs / Qes
Echo	The effect of a sound and a delayed version of that same sound. A 'Slap-Back Echo' is the original sound plus a single repeat; "Multiple Echo" is the original sound plus several repeats with the identical delay spacing and decay times.
Effect	A device which modifies sonic structures creatively with various processing techniques.
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 displaces sufficient air to produce a measurable 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 polarized capacitor with a negative and a positive terminal that is commonly used for DC power filtration and energy storage. As with all capacitors, the dielectric insulator separates two plates and holds a charge. In this case the dielectric is a form of chemical electrolyte that is polarized. Smaller types are measured in microfarads while the large ones used for amplifier stabilization are measured in farads. Values in the range of .5 to 3 farads are typical for use with car audio amplifiers.
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 back wave actually reinforces the front wave. Tweeters and midranges are less severely effected by the phase cancellation effects, and are not in need of enclosures.
Enclosure Volume	The total amount of internal airspace of an enclosure. Each woofer has an optimal airspace volume that helps it meet it's bass potential. This resonance cavity specification usually measured in cubic feet, includes the net driver and vent volumes. To find the volume of a cube multiply HxWxD in inches. divide the result be 1725 (the number of inches in a cubic foot) to get the volume in cubic feet.
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 equalizers 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.
Ergonomics	The accessibility and ease of controlling a system in normal operational mode with a minimum of motion and thought required.
ESP	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.
Excursion	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.
Expander	A type of dynamic range processor which reduces the gain of audio signals which are under an adjustable 'threshold' level, therefore increasing the dynamic range. Generally allows the operator control over threshold, ratio, attack, release and 'hold' times. Both analog and digital types are available.
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"
Fader	Rather like the right to left balance control, however the fader moves the sonic position between the front and back speakers.
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.
Fb	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.
Feedback	See acoustic feedback.
Fidelity	A term used to describe the accuracy of recording, reproduction, or general quality of audio processing. Getting it "high" is every designer's goal
Filter	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.
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).
Flux	The flow of magnetic energy in a circuit. Flux density is the measure of the strength of the magnetic field typically used in speakers, and which governs its power handling capacity.
Former	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.
Frequency	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 refers to the regular occurrence of compression and ratification 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	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.
Fuse	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.
Gain	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.
Generator	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.
Gig	Slang for job, engagement of musicians to play and perform.
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.
Grill	A barrier meant to prevent damage to the Driver that it covers, or that creates a more attractive appearance.
Ground	A term that describes anything having an electrical potential of zero relative to other points in a circuit. Most modern vehicles are designed around a negative ground system, with the metal frame being the vehicle's ground.
Ground Loop	The term given to the condition that occurs when a voltage potential exists between two separate ground points.
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.
Harness	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.
Headroom	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 transferring 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.
Hertz	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 Filter	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.
Horn	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)
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.
Hypercardioid	A narrower heart-shaped pick-up pattern than that of cardioid's microphones.
Imaging	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.
Impedance	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.
Infrasonic	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
Inductor	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.
Input Overload Distortion	Distortion caused by too great an input signal being sent to an amplifier or preamplifier. It is not affected by volume control settings and often occurs when micas are positioned too close to the sound source. This distortion may be controllable through the use of an attenuator or pad.
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.
IHF	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	s 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.
Interface	A device or protocol which facilitates the linking of any two devices or systems; or when used as a verb ('to interface'), the process of linking.
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.
Insulation or insulator	A non-conductive protective covering for electrically active parts and wire that prevents short circuits and other unwanted interference.
Inverse Square Law	In mathematics, the law that states that in the absence of reflective surfaces, sound pressure (or light) falls off at a rate inverse to the square of the distance from its source. In other words, every time the distance from the sound source is doubled, the sound pressure level is reduced by a factor of 4, or 12 dB.
Inverted Dust Cap (see Dust Cover/Cap)
Isobarik	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
Isolation	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.
Jack	A receptical for a plug used to interconnect electronic devices.
Joule	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 enables this action
Kapton	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.
Keypad	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 c