Audio Terms and Definitions (2022)

Audio terminology can be very confusing and ambiguous. Below is a basic listof most common words related to audio specifications and terminology.

Acoustic suspension - a sealed or closed box speaker enclosure. Alsoreferred to as an infinite baffle. Acoustic suspension speaker systems aregenerally less efficient than Bass Reflex or Transmission Line designs, butmay offer greater accuracy with respect to bass tightness and reproduction.

Acoustics - the science or study of sound.

Alternating (AC) Current - currents that have a harmonic time dependence.

Ampere (A) - the unit of measurement for electrical current in coulombsper second.

Amplifier - an electrical circuit designed to increase the currentor voltage of an applied signal.

Amplitude - the relative magnitude of a signal.

Attenuation - the reduction of an electrical signal.

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

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

Bandwidth - the range of frequencies reproduced by an amplifier ortransducer.

Band-Pass Enclosure - type of enclosure used for subwoofers wherethe driver is completely inside the enclosure and all of the output emergesthrough a port(s). This configuration is usually designed for high outputvolume with importance of accuracy/fidelity being less emphasized.

Band-Pass filter - an electric circuit designed to pass only midrangefrequencies. This filter acts as a high impedance to frequencies out of thepass band.

Bass (low frequencies) - The low end of the audio frequency spectrumbetween 0Hz to about 200 Hz.

Bass Reflex - see ported enclosure.

Bi-amping and bi-wiring - some higher performance speakers includedual sets of connectors, usually the type known as "binding posts," Modelswith dual connectors almost always also feature a special type of crossoverwith separate "high-pass" and "low-pass" sections. These connectors may alsobe shunted together with jumpers to accommodate conventional hook-ups.

Bi-wiring - low and high frequency sections of the loudspeaker areseparated electrically at the cross-over. Each driver unit has its own filtersection and connection terminals. Both sets of terminals are connected toone amplifer.

Bi-amping - an extension of bi-wiring in that a separate amplifieris utilized for each of the two sets of connectors from the cross-over.

Bipole -- A speaker design which generates equal amounts of soundboth forward and backward, with the two sounds being "in phase". See alsoDipole.

Capacitor - a charge storage device made up of two metallic platesseparated by a dielectric, with equal but opposite charges. The AC impedanceof a Capacitor is (1 / jWL) and acts as an open circuit in DC applications.

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

Class A - transistor amp conducts for the entire cycle of input signal,conduction angle 360 deg. Runs hot, as the transistors in the power amp areon all the time, but has high sound quality.

Class B - positive and negative halves of the signal dealt with bydifferent parts of the circuit, the output devices switching continually.Runs cooler, but the sound is not as pure.

Class AB - biasing the transistor amp at a non-zero DC current muchsmaller than the peek current of the signal source. Second transistor conductsduring negative half cycle of waveform and the currents from the 2 transistorsare combined at the load. A compromise between sound quality of Class A andefficiency of Class B. Most amp designs employ this method.

Clipping - a form of distortion caused by cutting off the peaks ofaudio signals. Clipping usually occurs in the amplifier when it's input signalis too large or when the voltage rails of the power supply cannot deliverthe necessary voltage to the power amp.

Coloration - any change in the characteristic of sound that reducesnaturalness, such as an overemphasis of certain tones.

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

Cone - the conical diaphragm of a speaker attached to the voice coilwhich produces pulsation's of air that the ear detects as sound.

Crossover Frequency - the frequency at which the driver's roll offat - usually when response is down -3dB. See Roll-off.

Crossover Network (Filter) - an electric circuit or network that splitsthe 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.

DAC - digital-to-analogue converter, turning on/off pulses into analoguesound. CD players have DACs built in. Separate DACs can upgrade a CDplayeror other digital player/ recorder, or can be used with dedicated CD transports.

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

Damping Factor - This is a quantity which defines how quickly theamplifier can stop a reproduced frequency such as a bass note. The higherthe damping factor, the better the amp will control the woofer and help reduceoverhang distortion. The damping factor of an amplifier is mostly dependenton the quality of the power supply which feeds the power amp.

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

Decibel (dB) - (1) a logarithmic scale used to denote a change inthe relative strength of an electric signal or acoustic wave. It is a standardunit for expressing the ratio between power and power level. Using the logarithmicrelationship for power PdB = 10*log[Pout/Pin] , a doubling of electrical poweronly yields an increase of +3 dB. Increasing the power tenfold will yieldan increase of +10 dB and is a doubling of perceived loudness. The decibelis not an absolute measurement, but indicates the relationship or ratio betweentwo signal levels. (2) SPL (sound pressure level) can be measured in dB. 0dB represents the threashold of normal human hearing, 130 dB represents thethreashold for pain, 140 dB causes irreparible hearing damage, and 150 dBcan cause instant deafness, anything greater than about 192 dB can kill you.

Diaphragm - the part of a dynamic loudspeaker attached to the voicecoil that moves and produces the sound. It usually has the shape of a coneor dome.

Diffusion - The scattering of sound.

Dipole - A speaker design which generates equal amounts of sound bothforward and backward, with the two sounds being out of phase. Dipoles areoften used as surround speakers. See also Bipole.

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

Diffraction - a change in the direction of a wave that is caused bythe wave moving past or hitting an obstacle.

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

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

Dome Tweeter - a high frequency speaker driver with a dome-shapeddiaphragm usually made of metal or silk.

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

Dynamic range - the range of sound intensity a system can reproducewithout compressing or distorting the signal.

Efficiency rating - the loudspeaker parameter that shows the levelof sound output when measured at a prescribed distance with a standard levelof electrical energy fed into the speaker (usually recorded as XdB @ 2.83Vinput signal from 1 meter of distance. However, a driver with a high efficiencyrating needs a larger box to play a lower frequency than a driver with a lowerefficiency rating.

Electronic Crossover - uses active circuitry in addition to passiveto filter unwanted signals for each driver. Usually active filters are employedas LPF(Low Pass Filters) for subwoofers or for the sub out of a preamp / receiver.

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

Equalizer - electronic device that acts as active filters used toboost or attenuate certain frequencies. Farad - the basic unit of capacitance.A capacitor has a value of one farad when it can store one coulomb of chargewith one volt across it.

Filter - any electrical circuit or mechanical device that removesor 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 which is the threshold ofhuman hearing sensitivity.

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

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

Frequency Response - the frequency range to which a system, or anypart of it, can respond.

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

Full-range - a speaker designed to reproduce all or most of the soundspectrum within human hearing (20Hz - 20KHz).

Ground - refers to a point of zero voltage or potential.

Group Delay - The group delay of a filter is a measurement of theaverage delay of the filter as a function of frequency. It is the negativefirst derivative of a filter's phase response.

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

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

HDCP (High-bandwidth Digital Content Protection) - This is a specification developed byIntel to address digital rights management. HDCP is used with HDTV signals over DVI (optional) and HDMI connections (mandatory) to prevent unauthorized duplication ofcopywritten material by inhibiting the unauthorized distribution of digital video material throughcopying. It consists of data "keys" incorporated in the digital contenttogether with proprietary encryption (scrambling) circuitry andsoftware in the various video components (tuner, TV, DVD player, etc.)that handle HDTV

HDMI (High Deifnition Multimedia Interface) - Now up to version 1.3, this digital video interface allows high definition video (up to and in excess of 1080p/60) and audio (up to 8 lossless channels) to be transmitted over a single cable. Except for some proprietary solutions (such as Impact Acoustics RapidRun Digital cables) HDMI cannot be terminate din the field and must be purchased in the correct lengths. Cables can be made of copper (limited to ~30 feet without electronic signal boost and equalization) or fiber optic, with the latter able to reach almost unlimited distances.

Hertz (Hz) - a measurement of the frequency of sound vibration. Onehertz 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 frequenciesbut blocks low ones by acting as a large impedance to those frequencies. SeeBand-pass and Low-pass filters.

Hiss - background audio noise that sounds like a Rattler snake. Justhope it is an audio source causing it and not a Rattler snake for your sake!

Home Theater - an audio system designed to reproduce the theater soundexperience while viewing movies in the home. A basic system usually consistsof a Dolby Prologic Decoder, 5 speakers and a subwoofer. More advanced systemsincorporate Dolby Digital/DTS and other discrete 5.1 channel surround formats.

Horn - a speaker design using its own funnel shaped conduit to amplify,disperse, or modify the sounds generated by the internal diaphragm of thespeaker. In most cases, these type of speakers should be avoided in home audio.

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

Imaging - it is the speakers ability to localize different instrumentsplaying simultaneously. See Soundstage.

Impedance - dependent on frequency, it is the AC equivalent of resistancein a DC circuit.

Inductance (L) - the capability of a coil to store energy in a magneticfield surrounding it. It produces an impedance to an AC current (jwL) andacts as a short circuit to DC. Inductors are commonly used in audio as lowpass crossovers. See Le.

Infinite Baffle - a flat surface that completely isolates the backwave of a driver from the front.

Infrasonic (Subsonic) Filter - a filter designed to remove extremelylow frequency usually between 8-25Hz or lower, noise from the audio signal.Useful for Ported box designs.

Input - connection from signal source.

Isobarik Enclosure - enclosure where one woofer is buried in the enclosureand a second is mounted up against the first and wired in reverse polarity(there are other variations for Isobarik designs), but this one works best.This allows the effective Vas of both drivers working in this push-pull configurationto be half that of a single identical driver mounted normally. Very smallenclosures may be constructed as a result, with increased power handling.Less efficient than other designs, but the push pull configuration greatlyreduces second order harmonic distortion. The name Isobarik comes from a termthat means "constant pressure". See push-pull.

Low-Pass Filter - an electric circuit designed to pass only low frequenciesand act as a high impedance to frequencies out of the filters passband. SeeBand-pass and High-pass filters.

Maximum power rating - a value which means almost nothing, but isused nonetheless by manufacturers to entice the unsuspecting into purchasingtheir product based solely on the big number. Technically, it is the maximumwattage that an audio component can deliver/handle as a brief burst duringa musical peak. Most reputable manufacturers will provide both an RMS andMax power rating. Typically, the given value for the maximum power ratingis twice to three times that of RMS.

Microfarads (mF) - a measurement of capacitance (XC*10^-6).

Midrange (mids) - the frequency range above bass but below treblethat carries most of the identifying tones of music or speech. It is usuallyfrom 200Hz to 4kHz.

Millihenries (mH) - a measurement of inductance (XL*10^-3).

Mms - the moving mass of a driver assembly.

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

MOFSET - Metal Oxide Semiconductor Field Effect Transistors. Usedin most modern, quality car audio amplifiers in the power supply (and sometimesin the output stage). MOSFET's run cooler than normal bipolar transistors,and have a faster switching speeds and higher slew rates.

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

Ohm - a unit of electrical resistance or impedance.

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

Oversampling - used in DAC systems. Increases signal frequency, makingit easier for conversion circuitry and ancillary systems to filter out unwantedsignals.

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 directproper frequencies to appropriate drivers. These crossover systems can besimple (First Order = 1 component @ -6 dB/octave slope) to complex (FourthOrder = 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 compliantdevice, with a similar cone material and surround found on regular activedrivers. The radiator must usually be at least as large (or larger) than thedriver it is aligned with. The passive radiator is tuned to Fb and used inplace of a port, providing bass reinforcement for the driver in a similarfashion as any regular ported box. A clear advantage of the radiator is theabsence of port noise, and some audiophiles claim the radiator provides abetter sounding bass than a ported enclosure. Disadvantages include difficultyin tuning, and the extra required baffle area for the radiator. Most radiatorscan be tuned with either weights or silicone, adding material in a balancedmanner until Fb is attained.

Peak - the maximum amplitude of a voltage or current.

Phase - Refers to the timing relationship of two or more signals orsoundwaves. It's especially important to be sure that your stereo speakersare playing "in phase." This means that the drivers (cones and domes) of yourright and left speakers are moving in and out at the same time. If your speakersare "out of phase" you'll hear significantly less bass, and instead of producinga strong center image, the sound tends to stay localized at the speakers.

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

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

PMPO - stands for peak music power, used on gear that needs to lookmore powerful than it is. If you see a boom -box, computer speakers or carreceivers advertising power rated like this, ignore it.

Polarity - the orientation of magnetic or electric fields. The polarityof the incoming audio signal determines the direction of movement of the speakercone. 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 orport to improve efficiency at low frequencies. Excellent design for lowerpower 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 frequencyroll-off is generally -24 dB/octave. Good transient response with proper tuning,although the driver loses damping below the tuning frequency. Excellent powerhandling about Fb, but source material or frequencies below Fb cause the driverto progressively perform as if it were not enclosed at all. Due to this, portedenclosures without a low frequency filter may have lower power handling comparedto other designs. More difficult to properly build and tune than a sealedenclosure, with several "optimum" alignments available depending upon theQts of the driver.

Power (P) - the time rate at which work is done or the rate at whichenergy is used. Basic equations for Electrical Power are: P = V^2/R or P =I^2*R.

Resonance - the tendency of an object to vibrate most at a particularfrequency.

Resonance Frequency - the frequency at which the speaker tends tovibrate most at a certain frequency.

Resistance (Re) - in electrical or electronic circuits, a characteristicof a material that opposes the flow of electrons. The higher the gauge ofwire, the less cross sectional area contributing to DC series resistance (DCR).

RMS - an acronym for "root mean square." Used in audio to help ratethe 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 upperfrequency range of a driver, network, or system. The roll-off frequency isusually defined as the frequency where response is reduced by -3 dB.

SACD - a high-resolution digital audio format developed bySony and Philips. Instead of using PCM audio encoding like standardCDs, SACDs use Direct Stream Digital (DSD) encoding. DSD is a 1-bittechnology that samples music at the rate of 2.82 million times persecond, compared to standard CD's rate of 44,100 times per second.SACDs typically sound more detailed than standard CDs, with greater dynamic range, and are mastered separately from the often compressed CDs.

Sampling rate - how fast a digital recorder or player samples a signal.CD, DCC and MiniDisc use a rate of 44.1kHz - ie 44,100 samples per second- while DATrecorders offer a choice of 48kHz or 44.1kHz, and Digital AudioBroadcasting will work on 32kHz. A digital-to-analogue converter needs towork on all three rates. The sampling rate determines the highest frequencyrecordable a digital system can carry - hence the development of higher-samplingformats, such as Pioneer's 96kHz system, for better treble extension.

Satellite speaker - A small speaker with limited bass response, oftendesigned to be used with a matching subwoofer.

Sealed enclosure - air tight enclosure that completely isolates theback wave of the driver from the front. Very tight, defined sound (with Qtc= 0.707) with very good transient response and power handling. Low frequencyroll-off is at -12 dB/octave. Less efficient than other designs, and higherdistortion levels at resonance. Easy to design and build.

Sensitivity - The sound pressure level directly in front of the speaker(on axis) at a given distance (usually 1 meter) produced by a given amountof power (usually 1 watt).

Signal-to-noise (S/N) - the ratio, expressed in dB, between the signaland 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. Audiosignals 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, mountedin a sealed chamber (Vr) and firing into a second ported chamber with thesound emanating from one or more ports. This second chamber (Vf) is tunedto the sealed drivers Fcb. Band-pass enclosures pass only a limited rangeof frequencies, negating the need for crossovers in the circuit. In a typicalsingle reflex bandpass, the cutoff rate below and above the "pass-band" isat a rate of -12dB/octave. These designs are very efficient within the operatingbandwidth, with superior power handling, but generally inferior transientresponse to sealed (all the sound has to come out of the vent). Transientresponse can be very good if the enclosure is configured with a S of 0.70.Can be very difficult to design and build.

Slew Rate - This is a term used to describe how quickly the outputof an amplifier can track its input. Slew Rate is usually measured in V /msec. The higher the value, the better the amp is at reproducing the subtlenuances and dynamics associated with music reproduction

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

Sound Stage - the sound systems ability recreate an imaginary stage.A good speaker will faithfully make the stage seem close to the actual height,width and depth of the actual performance stage where recorded. Imaging issimilar, but the speaker must be able to place each instrument or voice inthe correct location on the soundstage. The reproduction of the way the musicwould 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 frequencythat is dependent upon the dimensions of a resonant room, car interior, orenclosure. It occurs when the rate of energy loss equals the rate of energyinput into the system. This is what you hear when you listen into a sea shell.

Subwoofer - a loudspeaker designed to reproduce bass frequencies.

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

Timbre - The quality of a sound related to its harmonic structure.Timbre is what gives a voice or instrument its sonic signature -- why a trumpetand a saxophone sound different when they play the same note.

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

Total Harmonic Distortion (THD) - the RMS value of the harmonic componentsof the output signal, excluding the fundamental, expressed as a percentageof the RMS of the fundamental.

Transient Response - the ability of a speaker to respond to any suddenchange in the signal without blurring (smearing) the sound. A speaker thatcan react quickly to rapid changes in sound has "good transient response".

Transmission Line Enclosure - a design in which the driver is at oneend of the enclosure, with an internal path which consists of a series ofbends or curves that lead to a port at the other end of the enclosure. Thepath length is a fraction of the wavelength at low frequencies. The lengthof the path is increased by stuffing the box with either long fiber wool orpolyester batting, and produces a phase shift in the back wave that reinforcesbass at low frequencies. Enclosures must be very large, but low end responseof these systems is legendary among audiophiles. Drivers with Qts of lessthan 0.4 that work well in ported should work well in these designs, but nostandardized method for configuring these enclosures exists that engineershave 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 difficultenclosures to design and build, and much experimentation may be necessaryto get things right. "Labyrinths" and "Tapered (Stuffed) Pipes"are both variantsof this type of enclosure.

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

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

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

Voice-matched - Speakers that are "voice-matched" have a similar timbreor tonal quality. Voice-matched speakers in a home theater system will resultin more seamless, consistent, convincing wraparound sound.

Voice coil - the wire wound around the speaker former. The formeris mechanically connected to the speaker cone and causes the cone to vibratein 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 theuse of one joule of energy per second. Watts of electrical power equals voltstimes amperes.

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

Woofer - a loudspeaker transducer designed to reproduce low-frequencysounds.

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