Audio Glossary Glossary


It can get real confusing, audio terminology. Here is a list of most basic words and terms you will generally come across. I tried my best to keep things simple, but wanted to put down enough information to provide you with a definitive guide you can always come back to. Many thanks to my reference books, "Advanced Speaker Systems" by Ray Alden, "Great Sound Stereo Speaker Manual" by David B. Weems, and "Car Stereo Installation Made Easy" by Crutchfield . Many of these definitions were obtained from these sources, while others were simply squeezed from my own tired noodle. I have tried to include terms applicable for both car and home audio in this glossary.

If you think I have forgotten something important, please send me email with your idea and I'll try and add a definition.

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Acoustic suspension - a sealed or closed box speaker enclosure.

Alignment - a class of enclosure parameters that provides optimum performance for a woofer with a given value of Q.

Alpha - in sealed enclosure designs, the ratio of Vas to Vb, where Vb is the volume of the box you will build. See sealed enclosure.

Alternating Current (AC) - an electrical current that periodically changes in magnitude and direction.

Ampere (A) - the unit of measurement for electrical current in coulombs per second. There is one ampere in a circuit that has one ohm resistance when one volt is applied to the circuit. See Ohms Law.

Amplifier - an electrical circuit designed to increase the current, voltage, or power of an applied signal.

Aperiodic Enclosure - an otherwise sealed enclosure design, but with a vent that is stuffed with damping material, which flattens out the impedance curve of the design. The area of this resistive vent should be about 10 sq. in. per cubic ft. of enclosure volume. This design might take some experimentation with the vent stuffing, testing the impedance curve several times with different amounts of damping material until the flattest impedance curve is found. The aperiodic resistive vent damps the driver in much the same way as fully stuffing a sealed enclosure with damping material (100% fill). In this way, an optimum design may be made up to 20% (or more) smaller due to the extra damping of the resistive vent. Enthusiasts of this design often compare the performance with transmission line enclosures, advocating that the design avoids the "ringing" effects of ported enclosures while alleviating the "pressure effect" of the sealed box. Dynaudio sells a DIY insertable resistive vent called the Variovent.

Attenuation - the reduction, typically by some controlled amount, of an electrical signal.

Audio frequency - the acoustic spectrum of human hearing, generally regarded to be between 20 Hz and 20 kHz.

Audio Noise - see Noise.

Baffle - a board or other plane surface used to mount a loudspeaker.

Bandwidth - the range of frequencies covered by a driver or a network (crossover).

Band-pass Enclosure - see dual reflex bandpass and single reflex bandpass.

Band-pass filter - an electric circuit designed to pass only middle frequencies. See also High-pass and Low-pass filters.

Basket - the metal frame of a speaker.

"Bass Blockers" - first order high pass crossovers (non-polarized capacitors), generally used on midbass or dash speakers to keep them from trying to reproduce deep bass.

Bass (lows) - The low end of the audio frequency spectrum, from approximately 20 Hz up to 400 Hz or so.

Bass Reflex - a ported enclosure.

Beaming - the tendency of a loudspeaker to concentrate the sound in a narrow path instead of spreading it.

Boomy - the smearing of transients that makes bass reproduction sound muddled, usually because of improperly designed sealed (to small), ported (to small or tuned improperly), and bandpass enclosures, although the latter are sometimes designed this way on purpose by car audio manufacturers or install shops to be loud.

Bridging - combining both left and right stereo channels on an automotive amplifier into one higher powered mono channel. When an amplifier is bridged, the impedance that the amplifier actually "sees" is calculated based upon the output of both stereo channels. Here is a simple formula to help define this:

Bridged Mono Impedance = (Y / X)/2

Y = impedance of driver(s) (both drivers should be identical)

X = # of drivers in circuit

So, hooking up one 4 ohm sub bridged mono would be equal to hooking up two 2 ohm subs in stereo, one to each channel.

Cabin gain - the low frequency boost normally obtained inside a vehicle interior when subs are properly mounted.

Capacitor - a device made up of two metallic plates separated by a dielectric (insulating material). Used to store electrical energy in the electrostatic field between the plates. It produces an impedance to an ac current. In automotive applications, special "Power Line Caps" can be connected inline to the amplifier to aid the alternator in supplying current demands of amps. Non-polarized capacitors can be used as first order passive high pass crossovers, or as components in more complex high pass, bandpass and lowpass crossovers. See power line caps.

Center Channel - in home theater, sound decoded from the stereo signal sent to a speaker mounted in front of the listener, specially designed to enhance voices and sound effects from a movie soundtrack. Used in car audio to help offset skewed stereo imaging due to seating positions in the automotive environment.

Channel - the path an audio signal travels through a circuit during playback. At least 2 channels are required for stereo sound.

Circuit - a complete path that allows electrical current from one terminal of a voltage source to the other terminal.

Clipping - a distortion caused by cutting off the peaks of audio signals. Clipping usually occurs in the amplifier when it's input signal is too high or when the volume control is turned to high.

Cms - mechanical suspension compliance of a driver, consisting of the spider and surround.

Coaxial Driver - a speaker composed of two individual voice coils and cones; used for reproduction of sounds in two segments of the sound spectrum. See also triaxial driver.

Coulomb - 6.25 (10)^18 electrons per second.

Coloration - any change in the character of sound that reduces naturalness, such as an overemphasis of certain tones.

Compliance - the relative stiffness of a speaker suspension, specified as Vas.

Cone - the cone-shaped diaphragm of a speaker attached to the voice coil which produces pulsation's of air that the ear detects as sound.

Crossover Frequency - the frequency at which a driver's response is down -3dB. See Roll-off.

Crossover Network (Filter) - an electric circuit or network that splits the audio frequencies into different bands for application to individual speakers. See Electronic and Passive Crossover.

Current (I) - the flow of electrical charge measured in amperes.

Damping - the reduction of movement of a speaker cone, due either to the electromechanical characteristics of the speaker driver and suspension, the effects of frictional losses inside a speaker enclosure, and/or by electrical means.

Damping Material - any material added to the interior of a speaker enclosure to absorb sound and reduce out-of-phase reflection to the driver diaphragm (cone). Usually acoustic fiberglass, polyester batting, or Polyfill is used in speaker enclosures.

Decibel (dB) - a logarithmic scale used to denote a change in the relative strength of an electric signal or acoustic wave. It is a standard unit for expressing the ratio between power and power level. An increase of +3 dB is a doubling of electrical (or signal) power; an increase of +10 dB is a doubling of perceived loudness. The decibel is not an absolute measurement, but indicates the relationship or ratio between two signal levels.

Diaphragm - the part of a dynamic loudspeaker attached to the voice coil that moves and produces the sound. It usually has the shape of a cone or dome.

Direct Current (DC) - current in only one direction.

Diffraction - a change in the direction of a wave front that is caused by the wave moving past an obstacle.

Dispersion - the spreading of sound waves as it leaves a speaker.

Distortion - any undesirable change or error in the reproduction of sound that alters the original signal.

Dome Tweeter - a high frequency speaker with a dome-shaped diaphragm.

Double (Dual) Voice Coil (DVC) - a voice coil with two windings, generally subwoofers. Each voice coil can be connected to a stereo channel, or both voice coils can be wired in parallel or series to a single mono channel.

Driver - a loudspeaker unit, consisting of the electromagnetic components of a speaker, typically a magnet and voice coil.

Driver Parameters - the physical properties of a driver that determine it's electrical and acoustical behavior. The minimum parameters used in determining speaker enclosures are Fs, Qts, and Vas. See Thiele/Small Parameters.

Dual Reflex Bandpass Enclosure - sometimes called a 6th order bandpass. This design was engineered and patented by Bose® with their original AM-5® 6th Order BandpassAcoustimass® sub/satellite system (home speakers). In these designs, Vr is ported as well as Vf, so that there are 2 resonant frequencies. Vf and Vr are tuned about an octave apart, providing the driver with excellent damping at resonance, even further reducing distortion. This design is even more efficient than a single reflex bandpass, but with a compromise. The system has the same high frequency roll-off of -12 dB/octave, but low frequency cut-off is at -24 dB/octave (just like a regular ported enclosure). Power handling is excellent within it's frequency bandwidth, but these designs are similar to ported in that they are subject to low frequency noise upsetting the driver(s) below F3. Transient response is also rather poor, but these enclosures can be made to play very loud. One of the most difficult enclosures to build and tune.

Dynamic range - the range of sound intensity a system can reproduce without compressing or distorting the signal.

EBP - Efficiency Bandwidth Product. A rating that helps a builder determine whether a driver is suitable for a sealed or ported enclosure. EBP of less than 50 indicates the driver should be used in a sealed, 50 - 90 indicates flexible design options, over 90 indicates best for a ported enclosure.

EBP = Fs / Qes

Efficiency rating - the loudspeaker parameter that shows the level of sound output when measured at a prescribed distance with a standard level of electrical energy fed into the speaker. Note, however, that a driver with a high efficiency rating needs a larger box to play a lower frequency than a driver with a lower efficiency rating. This means that a low efficiency driver in a small box will actually have higher sub bass SPL's than a high efficiency driver in a similar small box!

Electronic Crossover - uses active circuitry to send signals to appropriate drivers. More efficient than passive crossovers.

Enclosure - the box that contains the driver(s).

Equalizer - electronic device used to boost or attenuate certain frequencies.

F3 - the roll-off frequency at which the driver's response is down -3dB from the level of it's midband response, sometimes called the cutoff frequency.

Fb - the tuned frequency of a ported box.

Fc or Fcb - the system resonance frequency of a driver in a sealed box.

Fs - the frequency of resonance for a driver in free air.

Farad - the basic unit of capacitance. A capacitor has a value of one farad when it can store one coulomb of charge with one volt across it.

Filter - any electrical circuit or mechanical device that removes or attenuates energy at certain frequencies. See Crossover Network.

Flat Response - the faithful reproduction of an audio signal; specifically, the variations in output level of less than 1 dB above or below a median level over the audio spectrum.

Free Air Resonance - the natural resonant frequency of a driver when operating outside an enclosure.

Frequency - the number of waves (or cycles) arriving at or passing a point in one second, expressed in hertz (Hz).

Frequency Response - the frequency range to which a system, or any part of it, can respond. Unless a limit of variation in intensity is stated, this specification is meaningless. i.e., you see a subwoofer in a ported enclosure with a rated response of 35 - 300 Hz. Means nothing. It could very well be that it is 35 - 300 Hz (-24 dB), which means the low frequency roll-off actually begins at around 70 Hz. It needs to read something like this: 35 - 300 Hz (- 3 dB), which gives 35 Hz as the actual roll off frequency.

Fundamental Tone - the tone produced by the lowest frequency component of an audio signal.

Full-range - a speaker designed to reproduce all or most of the sound spectrum.

Golden Ratio - the ratio of the depth, width, and height of a speaker enclosure, based on the Greek Golden Rectangle. Usually recommended for home speakers, difficult to use in car audio applications. The Ratio: W = 1.0, Depth = 0.618W, Height = 1.618W.

Ground - refers to a point of (usually) zero voltage, and can pertain to a power circuit or a signal circuit. In car audio, the single most important factor to avoid unwanted noise is finding and setting a good ground.

Harmonic - the multiple frequencies of a given sound, created by the interaction of signal waveforms.

Harmonic Distortion - harmonics artificially added by an electrical circuit or speaker, and are generally undesirable. It is expressed as a percentage of the original signal. See THD.

Head Unit - the in dash control center of a car audio system, usually consisting of an internal low powered amp, AM/FM receiver, and either a tape or CD player (or both).

Hertz (Hz) - a measurement of the frequency of sound vibration. One hertz is equal to one cycle per second. The hertz is named for H.R. Hertz, a German physicist.

High-pass Filter - an electric circuit that passes high frequencies but blocks low ones. See Band-pass and Low-pass filters.

Hiss - audio noise that sounds like air escaping from a tire.

Home Theater - an audio system designed to reproduce the theater sound experience while viewing movies in the home. Minimally consisting of a Dolby Pro Logic® surround sound receiver, left and right front speakers, a center channel speaker, and at least (1) surround sound speaker. These plus optional subwoofer(s), surround speaker(s), and digital formats such as Dolby Digital® can enhance the viewing experience by drastically improving the sound quality of movie soundtracks.

Hum - audio noise that has a steady low frequency pitch.

Imaging - see Soundstage.

Impedance - the opposition of a circuit or speaker to ac current; the combined effect of a speaker's resistance, inductance, and capacitance that opposes the current fed to it. It is measured in ohms and varies with the frequency of the signal.

Inductance (L) - the capability of a coil to store energy in a magnetic field surrounding it. It produces an impedance to an ac current. Inductors are commonly used in audio as low pass crossovers. See Le.

Infinite Baffle - a flat surface that completely isolates the back wave of a driver from the front without a standard enclosure.

Infrasonic (Subsonic) Filter - a filter designed to remove extremely low frequency (25Hz or lower) noise from the audio signal. Useful for Ported box designs.

Input - the current fed into a loudspeaker.

Isobarik Enclosure - enclosure where one woofer is buried in the enclosure and a second is mounted up against the first and wired in reverse polarity Isobarik Configuration(there are other variations for Isobarik designs, but this one is the best). This allows the effective Vas of both drivers working in this push-pull configuration to be half that of a single identical driver mounted normally. Very small enclosures may be constructed as a result, with increased power handling. Any variation of a normal enclosure can be made Isobarik - so you could conceivably have an Isobarik dual reflex bandpass, ect. (good luck tuning it, though). Less efficient than other designs, but the push pull configuration greatly reduces second order harmonic distortion. Originally, a variation of this design was patented by Ivan Tiefenbrun, who produces various audiophile components in Scotland under the name of Linn Products. The name Isobarik comes from a term that means "constant pressure". See push-pull.

Kilohertz (kHz) - one thousand hertz.

Le - the inductance of a driver's voice coil, typically measured at 1 kHz in millihenries (mH).

Low-Pass Filter - an electric circuit designed to pass only low frequencies. See Band-pass and High-pass filters.

Lobing - the tendency of a speaker system that consists of more than one driver to produce a lobed frequency response in space with in-phase reinforcement (lobes) from the various drivers occurring at some elevations and out-of-phase opposition (nulls) at points between the lobes.

Maximum power rating - a value which means almost nothing, but is used nonetheless by manufacturers to entice the unsuspecting into purchasing their product based solely on the big number. Technically, it is the maximum wattage that an audio component can deliver/handle as a brief burst during a musical peak. Most reputable manufacturers will provide both an RMS and Max power rating. Typically, the given value for the maximum power rating is twice to three times that of RMS. Automotive head units are a good example of this shady technique, as all the ones I have ever seen use this rating for the built in amplifier output. Use RMS for determining real world equipment capabilities. See WLS.

Microfarads (mF) - a measurement of capacitance.

Midbass - mid level bass, usually frequencies just above the sub-bass range, from around 100 - 400 Hz or so.

Midrange (mids) - the frequency range above bass but below treble that carries most of the identifying tones of music or speech. It is usually from 300 - 400 Hz to 3kHz or so.

Millihenries (mH) - a measurement of inductance.

Mms - the moving mass of a driver assembly.

Mono - monophonic sound. A method for reproducing sound where the signals from all directions or sources are blended into a single channel.

MOSFET - Metal Oxide Semiconductor Field Effect Transistors. Used in most modern, quality car audio amplifiers in the power supply (and sometimes in the output stage). MOSFET's run cooler than normal bipolar transistors, and have a faster switching speed.

Noise - any undesirable sound reproduced in an audio system.

Octave - a range of tones where the highest tone occurs at twice the frequency of the lowest tone.

Ohm - a unit of electrical resistance or impedance.

Ohm's Law - a basic law of electric circuits. It states that the current [I] in amperes in a circuit is equal to the voltage [E] in volts divided by the resistance [R] in ohms; thus, I = E/R.

Out of Phase - when your speakers are mounted in reverse polarity, i.e., one speaker is wired +/+ and -/- from the amp and the other is wired +/- and -/+. Bass response will be very thin due to cancellation.

Output - the sound level produced by a loudspeaker.

Passive Crossover - uses inductors (coils) and capacitors to direct proper frequencies to appropriate drivers. These crossover systems can be simple (First Order = 1 component @ -6 dB/octave slope) to complex (Fourth Order = 4 components @ -24 dB/octave slope).

Passive Radiator - a device that looks just like an ordinary driver, except it has no magnet or voice coil. A radiator is usually a highly compliant device, with a similar cone material and surround found on regular active drivers. The radiator must usually be at least as large (or larger) than the driver it is aligned with. The passive radiator is tuned to Fb and used in place of a port, providing bass reinforcement for the driver in a similar fashion as any regular ported box. A clear advantage of the radiator is the absence of port noise, and some audiophiles claim the radiator provides a better sounding bass than a ported enclosure. Disadvantages include difficulty in tuning, and the extra required baffle area for the radiator. Most radiators can be tuned with either weights or silicone, adding material in a balanced manner until Fb is attained.

Pe - Driver's rated RMS power handling capability.

Peak - the maximum amplitude of a voltage or current.

Peak power rating - see Maximum power rating.

Peak-to-Peak power rating - a totally unreliable value of rating power amplifiers, often 4 times (or more!) the actual RMS output. See WLS.

Phase Coherence - the relationship and timing of sounds that come from different drivers (subs, mids, tweets) mounted in different locations in the vehicle.

Phase Distortion - a type of audible distortion caused by time delay between various parts of the signal; can be caused by equalizers.

Polarity - the orientation of magnetic or electric fields. The polarity of the incoming audio signal determines the direction of movement of the speaker cone. Must be observed when wiring speakers, so that they are "in phase". See Out of Phase.

Ported Enclosure - a type of speaker enclosure that uses a duct or port to improve efficiency at low frequencies. Excellent design for lower power systems, as the port often adds up to +3 dB to low frequency efficiency. F3 can be set considerably lower with proper design, although low frequency roll-off is generally -24 dB/octave. Good transient response with proper tuning, although the driver loses damping below the tuning frequency. Excellent power handling about Fb, but source material or frequencies below Fb cause the driver to progressively Portedperform as if it were not enclosed at all. Due to this, ported enclosures without a low frequency filter may have lower power handling compared to other designs. More difficult to properly build and tune than a sealed enclosure, with several "optimum" alignments available depending upon the Qts of the driver. I highly recommend Vance Dickason's "The Loudspeaker Design Cookbook," which goes into great detail concerning the different possible alignments of ported enclosures. The best way to model these alignments is with a software program, where changes in tuning and enclosure size can be immediately noted. Though it can be dated to the 1930's, the ported alignments were thoroughly researched and standardized by A.N. Thiele in the 60's and R. Small in the 70's. This work was further expanded by D.B. Keele and others.

Power (P) - the time rate of doing work or the rate at which energy is used. One equation for Power:

P = Volts^2 / Impedance

Power Line Capacitor - wired inline on the power lead with your car amp, this device stores current for instant release when short bursts of energy are needed to produce loud, deep bass notes. Best to mount as close to amp as possible.

Pressure Effect - in sealed box designs, the pressure build-up on one side of the cone which may cause non-linearity and inhibit dynamic range in the low bass.Sunfire True Subwoofer

Push-Pull Configuration - one driver is mounted normally, the second is mounted so that it faces into the enclosure, both sharing the same internal volume and wired out of phase with one another. Although electrically out of phase with one another, the drivers are acoustically in phase since they move in the same direction. This alignment theoretically reduces second order harmonic distortion. Bob Carver has done a great deal of research into this area, and has manufactured the Sunfire True Subwoofer, a unique push-pull design that utilizes a special passive radiator. Check out the white paper description! Wow!

Q - the magnification of resonance factor of any resonant device or circuit. A driver with a high Q is more resonant than one with a low Q.

Qes - the electrical Q of the driver.

Qms - the mechanical Q of the driver.

Qts - the total Q of the driver at Fs. Qts = Qes x Qms/Qes + Qms.

Qtc - value for the damping provided for a driver in a sealed enclosure. Denotes the enclosures ability to control the driver response at resonance. Qtc = 0.707 is the optimum value for sealed enclosures, providing flattest response and highest SPL for deep bass extension. Enclosures for this value are often rather large. Lower Qtc can give even better transient response, down to a Qtc of 0.577 for the best damping and transients, but the enclosure is usually huge and SPL's are down. A Qtc of 1.0 is a compromise between deep bass and transient response vs. smaller sized enclosure. Larger subs can go with an even higher Qtc, as their resonant frequency is often very low, but Qtc's above 1.5 can begin to sound very muddled and boomy, and sacrifice deep bass extension and transient response for enhanced mid-bass peaks (louder). Check out Enclosure Dilemma: Ported vs. Sealed, an article on this web site that gives more information about Qtc.

Rear fill - in autosound, the ambience created by a pair of rear speakers that helps complete the soundstage. A set of high quality components for the front powered by an external amp and a set of coax mounted on the rear deck powered by the head unit or small amp is a good example of a rear fill application. Rear fill speakers should be faded so that they create a richer ambience, but you should not be able to isolate any sounds coming from them.

Resonance - the tendency of a speaker to vibrate most at a particular frequency.

Resonance Frequency - the frequency at which any system vibrates naturally when excited by a stimulus.

Resistance (Re) - in electrical or electronic circuits, a characteristic of a material that opposes the flow of electrons. Speakers have resistance that opposes current.

RMS - an acronym for "root mean square." Used in audio to help rate the continuous power output of an amplifier or input capability of speakers. This is the preferred method for comparing anything in audio applications.

Roll-off (cut-off) - the attenuation that occurs at the lower or upper frequency range of a driver, network, or system. The roll-off frequency is usually defined as the frequency where response is reduced by -3 dB.

S or (Q') - the overall damping of a 4th order bandpass enclosure. i.e., if you were to figure a 4th order bandpass enclosure with a Qtc of 0.70 for Vr (the sealed chamber), then you would also figure Vf (ported chamber) with an S of 0.70. See Useful Conversions and Formulas for more information and the formulas involved.

Sd - effective piston area of a driver.

Sealed enclosure - air tight enclosure that completely isolates the back wave of the Sealeddriver from the front. Very tight, defined sound (with Qtc = 0.707) with very good transient response and power handling. Low frequency roll-off is at -12 dB/octave. Less efficient than other designs, and higher distortion levels at resonance. Easy to design and build. Originally this design was pioneered and marketed by companies like Acoustic Research. See Qtc.

Signal - the desired portion of electrical information.

Signal-to-noise (S/N) - the ratio, expressed in dB, between the signal and noise.

Sine wave - the waveform of a pure alternating current or voltage. It deviates about a zero point to a positive value and a negative value. Audio signals are sine waves or combinations of sine waves.

Single Reflex Bandpass Enclosure - sometimes called a 4th order bandpass. A design where the driver is completely "buried" in the enclosure, mounted in a4th Order Bandpass sealed chamber (Vr) and firing into a second ported chamber with the sound emanating from one or more ports. This second chamber (Vf) is tuned to the sealed drivers Fcb. Band-pass enclosures pass only a limited range of frequencies, negating the need for crossovers in the circuit. In a typical single reflex bandpass, the cutoff rate below and above the "pass-band" is at a rate of -12dB/octave. These designs are very efficient within the operating bandwidth, with superior power handling, but generally inferior transient response to sealed (all the sound has to come out of the vent). Transient response can be very good if the enclosure is configured with a S of 0.70. Can be very difficult to design and build. These enclosures have been around since the 1950's, and companies like KEF helped pioneer the manufacture and marketing of this design. See also Dual reflex bandpass.

Skin Effect - technically, a physical phenomenon that relates to the limited penetration into a conductor of an RadioFrequent signal according to its frequency. In a direct current case everything is constant and so nothing seems to happen. With an alternating current, however, there is a delay in the magnetic field's response to the change in current and the 'old' magnetic field tends to push the current towards the outside of the conductor. As the frequency increases, so does the effect until at very high frequencies the entire current flows in a very narrow skin on the conductor - hence the name. Skin effect is negligable in car audio applications. (The full article can be found here). Thanks Wim!

Sound Pressure Level (SPL) - the loudness of an acoustic wave stated in dB that is proportional to the logarithm of its intensity.

Sound Stage - the sound systems ability to correctly place instruments on an imaginary soundstage; reproduction of the way the music would sound if you were actually watching the musicians play in front of you. The stage should always appear to be in front of you, with a proper "image" of where each musician is playing on the imaginary soundstage.

Spider - the flexible material that supports the former, voice coil, and inside portion of the cone within the speaker frame.

Standing wave - a buildup of sound level at a particular frequency that is dependent upon the dimensions of a resonant room, car interior, or enclosure. It occurs when the rate of energy loss equals the rate of energy input into the system. This is what you hear when you listen into a sea shell.

Sub-bass - portion of bass that is very low, usually from 20 Hz - 100 Hz or so.

Subwoofer - a loudspeaker designed to reproduce sub-bass frequencies.

Surround (suspension) - the outer suspension of a speaker cone; holds the diaphragm in place but allows it to move when activated. Usually made of foam or rubber.

Surround Sound - usually representative of the monophonic sound extracted from the stereo signal sent to smaller rear or side speakers used in a home theater.

Thiele/Small parameters - numbers that specify the behaviour of drivers, as defined and analyzed by two engineers, Neville Thiele and Richard Small. See Driver Parameters.

Three-way - a type of speaker system composed of three ranges of speakers, specifically a woofer, midrange, and tweeter.

Total Harmonic Distortion (THD) - the percentage, in relation to a pure input signal, of harmonically derived frequencies introduced in the sound reproducing circuitry and hi-fi equipment (including speakers).

Transient Response - the ability of a speaker to respond to any sudden change in the signal without blurring (smearing) the sound.Panga Ribbon Transmission Line Loudspeaker

Transmission Line Enclosure - a design in which the driver is at one end of the enclosure, with an internal path which consists of a series of bends or curves that lead to a port at the other end of the enclosure. The path length is a fraction of the wavelength at low frequencies. The length of the path is increased by stuffing the box with either long fiber wool or polyester batting, and produces a phase shift in the back wave that reinforces bass at low frequencies. Enclosures must be very large, but low end response of these systems is legendary among audiophiles. Drivers with Qts of less than 0.4 that work well in ported should work well in these designs, but no standardized method for configuring these enclosures exists that engineers have yet to agree upon. Power handling is generally less than in other designs, but drivers may be capable of responding down to Fs. One of the most difficult enclosures to design and build, and much experimentation may be necessary to get things right. "Labyrinths" and "Tapered (Stuffed) Pipes"are both variants of this type of enclosure. Check out the Panga transmission line speaker manufactured by Davidson Loudspeakers.

Treble (highs) - the upper end of the audio spectrum reproduced by tweeters, usually 3 - 4 kHz and up.

Triaxial driver - a speaker that is composed of three individual voice coils and cones; used for the reproduction of sounds in three segments of the sound spectrum.

Tri-way output - when a special passive crossover is used with an automotive amplifier to safely power a subwoofer in bridged mono (low pass circuit) as well as a pair of stereo speakers (high pass circuit). Normal inductors and capacitors can be used for Tri-way output.

Tweeter - a speaker designed to reproduce the high or treble range of the sound spectrum.

Two-way - a type of speaker system composed of two ranges of speakers, usually a woofer and tweeter.

Vas - the equivalent volume of compliance, which specifies a volume of air having the same compliance as the suspension system of a driver.

Vb - total box volume, usually in cubic feet or liters. Used specifically in sealed and ported designs.

Vf - front volume of a bandpass design.

Vr - rear volume of a bandpass design.

Voice coil - the wire wound around the speaker former. The former is mechanically connected to the speaker cone and causes the cone to vibrate in response to the audio current in the voice coil.

Volt (E) - a unit of measurement used to measure how much "pressure" is used to force electricity through a circuit.

Watt - a unit of electrical power. A watt of electrical power is the use of one joule of energy per second. Watts of electrical power equals volts times amperes.

Wavelength - the length of a sound wave in air. It can be found for any frequency by dividing the speed of sound in air (1120 feet per second) by the frequency of the sound, or: WL = 1120 / Freq.

Whizzer - a small supplementary cone attached to the center of the speaker's main cone for the purpose of increasing high frequency response.

WLS - When Lightning Strikes. The power ratings that you see provided on head units or cheap amps and stereo equipment that means absolutely nothing. If you see equipment with an impossible exaggerated rating, just say no. OK, I made this one up, but I think it is rather appropriate. Maybe the Federal Trade Commission will see this page…

Woofer - a bass loudspeaker designed to reproduce low-frequency sound only. A woofer and subwoofer are usually the same type of loudspeaker, but their application (crossover frequency) differentiates them.

Xmax - maximum linear cone excursion of a driver, measured in inches or millimeters. Check out what JL Audio has to say about Xmax and acoustic output relationships!

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