Sound Terms & Glossary

A

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A-B Test:- A test between two components. For example, a test between two different microphones for comparison or suitability

Absorption:-  The ability of a room to take up or absorb the acoustic energy radiated within it. There are many types of absorption since it can be frequency dependent. There are certain materials such as acoustical ceilings that may absorb more high frequencies than lows. Diaphragmatic absorptions (caused by loose wall panels or cavities behind the panels) cause certain low frequencies to be absorbed.

Acoustic:-  Relating to the production, effects and transmission of sound waves; the transmission of sound waves through various mediums. Pertaining to the act or sense of hearing, the science of sound, or the sound heard.

Acoustical:- Sound or properties of sound; the acoustical response of a room has to do with the way that room responds to sound.

Acoustic Treatment:- The application of acoustic or sound absorbing material to a room or enclosure to obtain the desired acoustic characteristics.

Active:- A type of electronic circuitry that can increase the gain or amplitude of a signal. Active gain controls. Active Equalization. Active Direct Boxes. Active Crossover.

Acoustic suspension:- A sealed or closed box speaker enclosure. The acoustic-suspension woofer (sometimes known as "air suspension") uses the elastic cushion of air within a sealed enclosure to provide the restoring force for the woofer diaphragm.

AES/EBU:- Balanced digital connection. For example, used to connect a CD transport to a DAC. The AES/EBU standard uses XLR type connectors..

Alternating Current (AC):- Or the mains socket on the wall. An electrical current that periodically changes in magnitude and direction in the U.K. this happens 50 times a second

Ambience:- The acoustic characteristics of an enclosed environment with regard to short delay and reverberation. A room with a lot of reverb is said to be "live"; one without much reverb is "dead."

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 (Amp): A device which increases signal level. Many types of amplifiers are used in audio systems. Amplifiers typically increase voltage, current or both.

Amplifier classes: Audio power amplifiers are classified primarily by the design of the output stage. Classification is based on the amount of time the output devices operate during each cycle of signal swing. Also defined in terms of output bias current, (the amount of current flowing in the output devices with no signal). · Class A operation is where both devices conduct continuously for the entire cycle of signal swing, or the bias current flows in the output devices at all times. The key ingredient of class A operation is that both devices are always on. There is no condition where one or the other is turned off. Because of this, class A amplifiers are single-ended designs with only one type polarity output devices. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, class A amplifiers are large, heavy and run very hot. All this is due to the amplifier constantly operating at full power. The positive effect of all this is that class A designs are inherently the most linear, with the least amount of distortion.
· Class B operation is the opposite of class A. Both output devices are never allowed to be on at the same time, or the bias is set so that current flow in a specific output device is zero when not stimulated with an input signal, i.e., the current in a specific output flows for one half cycle. Thus each output device is on for exactly one half of a complete sinusoidal signal cycle. Due to this operation, class B designs show high efficiency but poor linearity around the crossover region. This is due to the time it takes to turn one device off and the other device on, which translates into extreme crossover distortion. Thus restricting class B designs to power consumption critical applications, e.g., battery operated equipment, such as 2-way radio and other communications audio. · Class AB operation allows both devices to be on at the same time (like in class A), but just barely. The output bias is set so that current flows in a specific output device appreciably more than a half cycle but less than the entire cycle. That is, only a small amount of current is allowed to flow through both devices, unlike the complete load current of class A designs, but enough to keep each device operating so they respond instantly to input voltage demands. Thus the inherent non-linearity of class B designs is eliminated, without the gross inefficiencies of the class A design. It is this combination of good efficiency (around 50%) with excellent linearity that makes class AB the most popular audio amplifier design.
· Class AB plus B design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B.
· Class D operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle. Since the output devices are either completely on or completely off they do not theoretically dissipate any power. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product we're still waiting for; meanwhile designs do exist with true efficiencies approaching 90%.
· Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs.
· Class H operation takes the class G design one step further and actually modulates the higher power supply voltage by the input signal. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices. The efficiency of class H is comparable to class G designs.
Anechoic Refers to a room in which all surfaces are lined with acoustic absorption material to such an extent that the room absorbs sound energy instead of reflecting it around the room (no echo). A room that offers nearly total absorption is called an Anechoic Chamber and must be quite large in order to accommodate low frequencies.
Analogue: Before digital, the way all sound was reproduced. Whereas digital is built up of blocks and is dependant on the resolution for how detailed control can be. Analogue is continuously variable

Aperiodic: 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 lower the Q of the system and reduce the impedance peak at resonance. Most restrictive ports are heavily stuffed with fibreglass, Dacron or foam.

Attenuation A decrease in signal magnitude from one point to another, or the process causing this decrease.

Attenuator An adjustable passive network which reduces the power level of a signal without introducing any appreciable distortion.

Aux Input / Aux Output An auxiliary input or output that is generally a direct connection to the device's internal signal bus. These are used to interconnect devices which have the same signal level. That is, where gain is not required such as when connecting a microphone to a mixer. Typical devices that operate at "aux level" are tape decks, CD players, equalizers, signal processors, etc.

AWS: Adaptive Woofer System, trademark of ACI. An active woofer system with built in user adjustable equalization capabilities.

B

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Baffle The panel on which the speaker is mounted within the speaker enclosure. The term derives from its original use in preventing or baffling the speaker's rear sound waves from interfering with its front waves.

 

Baffle: A surface used to mount a loudspeaker.

Balanced: Referring to wiring: Audio signals require two wires. In an unbalanced line the shield is one of those wires. In a balanced line, there are two wires plus the shield. For the system to be balanced requires balanced electronics and usually employs XLR connectors. Balanced lines are less apt to pick up external noise.

Bandwidth: The total frequency range of any system. Usually specified as something like: 20-20,000Hz plus or minus 3 db.

Band-pass Enclosure: A multi-chambered ported system designed to restrict the speaker to be most efficient over a selected bandwidth.

Band-pass filter: An electric circuit designed to pass only middle frequencies. For example in a three way passive crossover lets mid range throu7gh to the mid range speaker.

Bass Blockers: Commercial name for auto-sound 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 Reflex: A type of loudspeaker that uses a port or duct to enhance the low-frequency response. Opinions vary widely over the "best" type of bass cabinet, but much has to do with how well a given design, such as a bass reflex is implemented.

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

Bessel crossover: A type of crossover design characterized by having a linear or maximally flat phase response. Linear phase response results in constant time-delay (all frequencies within the pass band are delayed the same amount). Consequently the value of linear phase it reproduces is a near-perfect step response with no overshoot or ringing. The downside of the Bessel is a slow roll-off rate. The same circuit complexity in a Butterworth response rolls off much faster.

Bi-amplify: The use of two amplifiers, one for the lows, one for the highs in a speaker system. Could be built into the speaker design or accomplished with the use of external amplifiers and electronic crossovers.

Bi-wiring: The use of two pairs of speaker wire from the same amplifier to separate bass and treble inputs on the speaker.

BNC: A type of connection often used in test 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: Listening term, refers to an excessive bass response this could be from speaker and box design or an acoustic anomaly of the room or a combination of the two

Bright: Listening term. Usually refers to too much upper frequency energy.

Bridging: Combining both left and right stereo channels on an 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
One 4-ohm sub in bridged mono is equal to hooking up two 2-ohm subs in stereo, one to each channel.

Bus A conductor that serves as a common connector to several signal sources, most often associated with a mixer. A separate signal routing to a specified output.

Butterworth crossover: A type of crossover circuit design having a maximally flat magnitude response, i.e., no amplitude ripple in the passband. This circuit is based upon Butterworth functions, also know as Butterworth polynomials.

C

Cardioid A type of microphone having a heart shape pickup pattern that picks up sound better from the front (on axis) than back (off axis). [See Unidirectional]

Centre Channel: In home theatre, 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.

Clipping: Refers to a type of distortion that occurs when an amplifier is driven into an overload condition. Usually the "clipped" waveform contains an excess of high-frequency energy. The sound becomes hard and edgy. Hard clipping is the most frequent cause of "burned out" tweeters. Even a low-powered amplifier or receiver driven into clipping can damage tweeters which would otherwise last virtually forever.

Class A, Class A-B etc.: In a sense, amplifying the audio signal means using the wall-current (usually either 120 or 240 volts) to increase the amplitude of the audio signal from mill-watts to watts. Different classes of amplifiers accomplish this in different ways. Turning a vacuum tube "on" or "off" with current demand increases the efficiency of the amplifier but may add switching distortion. A Class A amplifier is relatively inefficient, converting much energy to heat, but has no switching distortion.

Cluster An array of loudspeakers or horns designed to act as a single or point source of sound.

Cms: Mechanical suspension compliance of a driver, consisting of the spider and surround.

Co-axial or Coaxial Driver: speaker type that utilizes a tweeter mounted at the centre of a woofer cone. The idea being to have the sound source through the full frequency range is from the same point See also triaxial driver.

Coherence: Listening term. Refers to how well integrated the sound of the system is.
Coloration: Listening term. Meaning that the original sound has been added to or subtracted from either electronically or acoustically

Comb Filter When two combining sound waves have different amplitudes, phases, and frequencies, the resultant soundwave develops many nulls or spaces where the energy has cancelled. When viewed on a graphic recorder the resultant frequency response resembles a comb due to the nulls or notches of information that have cancelled.

Compander A combination of a compressor at one point of a signal path for reducing the level of the signal, followed by an expander at another point for a complimentary increase in signal level.

Compression: In audio, compression means to reduce the dynamic range of a signal. Compression may be intentional or one of the effects of a system that is driven to overload.

Compression Driver The high frequency element in 2/3-way speaker system which is then mounted to a horn mouth

Continuous Power This power rating represents the most conservative statement of the capability of an amplifier. It is also called "RMS" power. It denotes the amount of power an amplifier can deliver when amplifying a constant steady tone. It is usually measured at a signal frequency of 1kHz for a specific distortion. Continuous power in watts is expressed as: W = V2/R Power in watts equals the voltage squared divided by the resistance of the load.
Critical Distance The point within a room where the sound level of the direct field radiating from the loudspeaker and the reverberant field within the room become equal in intensity or level.

Crossover: A frequency divider. Crossovers are used in speakers to route the various frequency ranges to the appropriate drivers. Additionally, many crossovers contain various filters to stabilize the impedance load of the speaker and or shape the frequency response. Some crossovers contain levels controls to attenuate various parts of the signal.
A passive crossover uses capacitors, coils and resistors, usually at speaker level. A passive crossover is load dependent (the transition may not be very smooth or accurate if a different speaker is substituted for the one the crossover was designed for).
An active crossover is based on integrated circuits (ICs), discreet transistors or valves active crossover is impedance buffered and gives a consistent and accurate transition regardless of load.

Crossover Slope: High and low pass filters used for speakers do not cut-off frequencies like brick walls. The roll off occurs over a number of octaves. Common filter slopes for speakers are 1st through 4th order corresponding to 6db/oct to 24db/oct. For example, a 1st. order, 6db/oct high pass filter at 100hz will pass 6db less energy at 50Hz and 12db less energy at 25Hz. Within the common 1st through 4th filters there is an endless variety of types including Butterworth, Linkwitz-Riley, Bessel, Chebychev, etc. Salesmen and product literature will sometimes make claims of clear superiority for the filter used in the product they are trying to sell. Since the subject fills books, suffice it to say that there is no one best filter, it depends on application and intended outcome. Good designers use the filters required to get the optimum performance from the system.

Cross-talk: Unwanted breakthrough of one channel into another. Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.

Current (I): The flow of electrical charge measured in amperes.

D
DAC: A Digital to analogue converter. Converts a digital bit stream to an analogue signal. Can be a separate "box" that connects between a CD Transport or CD Player and a pre-amplifier.
Damping (Damping factor, etc.): Refers to the ability of an audio component to "stop" after the signal ends. For example, if a drum is struck with a mallet, the sound will reach a peak level and then decay in a certain amount of time to no sound. An audio component that allows the decay to drag on too long has poor damping, and less definition than it should. An audio component that is over damped does not allow the initial energy to reach the full peak and cuts the decay short. "Boomy" or "muddy" sound is often the result of under damped systems. "Dry" or "lifeless" sound may be the result of an over damped system.
dB (Decibel)- A unit for describing the ratio of two voltages, currents, or powers. The decibel is based on a logarithmic scale; when measuring differences in sound pressure level (SPL), the amount of change in sound pressure level perceivable is directly proportional to the amount of stimulus (the more sound present, the greater the change must be, to be perceived).
· 0 dB is the threshold of hearing, 130 dB is the threshold of pain.
· Whisper: 15-25 dB
· Quiet background: about 35 dB
· Normal home or office background: 40-60 dB
· Normal speaking voice: 65-70 dB
· Orchestral climax: 105 dB
· Live Rock music: 120 dB+
· Jet aircraft: 140-180 dB
Decay The gradual reduction in sound energy once the sound source is turned off.
Diaphragm A thin flexible sheet that can be moved by sound waves as in a microphone, or can produce sound waves when moved as in a loudspeaker or compression driver.
Diffraction The bending or redistribution of acoustic sound waves in a room caused by some obstacle, such as a column or divider. Only low frequency waveforms can be diffracted.
Diffusion The scattering of sound waves by a solid object.

Digital Refers to the processing of audio signals as having discrete values as opposed to a continuous analogue audio signal. In digital audio the continuous analogue signal is converted to an encoded discrete value or digital word.

Dip A reduction (attenuation or cut) in gain at a certain frequency also called a notch

Dipole: An open-back speaker that radiates sound equally front and rear. The front and rear waves are out of phase and cancellation will occur when the wavelengths are long enough to "wrap around". The answer is a large, wide baffle or to enclose the driver creating a monopole.

Direct Current (DC): Current that moves in only one direction. A battery is D.C.

Direct Injection Box (D.I.) A means of connecting non-balanced sources keyboards, guitars ECT. To a balanced line enabling the sound to be sent down a long cable without noise. Passive D.I. require no voltage and usually consist of a transformer. Passive D.I. are considered inferior to active D.I. boxes which have more complex electronics and need a power supply either battery or phantom power

Directivity Area of coverage of a speaker or microphone.

Dispersion: The spreading of sound waves as they leave a source.

Distortion: Guitarists often add distortion through a pedal that overdrives the signal resulting in a clipped or distorted sound intentionally.
Anything that alters the musical signal. There are many forms of distortion, some of which are more audible than others. Distortion specs are often given for electronic equipment which is quite meaningless. As in all specifications, unless you have a thorough understanding of the whole situation, you will not be able to make conclusions about the sonic consequences.

DIY: Abbreviation for Do - It - Yourself. In audio, the most common DIY is building speakers but some hobbyists build everything from pre-amps to amplifiers to DACs.

Dolby Digital: Is a five-channel system consisting of left, centre, right and left rear, right rear channels. All processing is done in the digital domain. Unlike Dolby Prologic in which the rear effects channels are frequency limited to approx. 100-7000Hz, Dolby Digital rear channels are specified to contain the full 20-20Khz frequency content. The AC3 standard also has a separate subwoofer channel for the lowest frequencies.

Dolby Digital EX Surround: Also referred to as Dolby Digital 6.1, adds a rear, centre channel to the existing left, centre, right and rear speakers. This format requires a 6.1 processor or receiver and DVDs that are 6.1 encoded.

Dolby Prologic: Is a four-channel system consisting of left, centre, right and rear channel, (the single rear channel is usually played through two speakers).

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

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

Driver The motor structure portion of a horn loaded loudspeaker system that converts electrical energy into acoustical energy and feeds that acoustical energy into the entry of a horn throat or the narrow end of the horn. Most often used when referring to a high frequency compression driver, called a driver for short. The definition also includes the loudspeaker in a horn-loaded woofer or mid bass horn

DTS: Digital Theatre System. A multi-channel encoding/decoding system. Used in some movie theatres. Also now included in some home-theatre processors. A competitor to Dolby Digital.

DSP: Digital Signal Processing. DSP most communally used to create effects such as reverb, delay, equalization, compression, etc. of a digital signal.

DVD: Digital Video Disc or Digital Versatile Disc. A relatively new standard that seeks to combine better-than-laser-disc quality video with better-than-CD quality audio in a disc the size of a CD. Requires special players. Seems to be a viable candidate to replace both Laser discs and CDs, but the jury is still out.

Dynamic Headroom: The ability of an audio device to respond to musical peaks. For example, an amplifier may only be capable of a sustained 100 watts, but may be able to achieve peaks of 200 watts for the fraction of a second required for an intense, quick sound. In this example the dynamic headroom would equal 3 db.

Dynamic range: The range between the loudest and the softest sounds that are in a piece of music, or that can be reproduced by a piece of audio equipment without distortion (a ratio expressed in decibels). In speech, the range rarely exceeds 40 dB; in music, it is greatest in orchestral works, where the range may be as much as 75 dB.

E

Echo
A wave which has been reflected or otherwise returned with sufficient magnitude and delay to be perceived as a distinct wave, separate from the original wave. A delay in sound of more than 50 milliseconds resulting in a distinct repeat or number of repeats of the original sound.

Efficiency rating: The loudspeaker parameter that gives the level of sound output when measured at a prescribed distance with a standard level of electrical energy fed into the speaker. A figure of 101 db 1watt 1metre would be very efficient. A figure of 91db 1watt 1 metre would be 1/10th as efficient.

Electronically Balanced Input A differentially balanced amplifier; an amplifier whose output is proportional to the difference between the voltages applied to its two inputs. Offers common mode rejection or attenuation of interference signal that was introduced electromagnetically in the signal carrying conductors.

Electronic Crossover: Uses active circuitry to send signals to appropriate drivers. More efficient than passive crossovers.

Electrostatic Speaker: A speaker that radiates sound from a large diaphragm that is suspended between high-voltage grids. This principal is reversed in condenser microphones.

Enclosure An acoustically designed housing or structure for a speaker.

Equalizer: Electronic set of filters used to boost or attenuate certain frequencies.

F

Fb: The tuned frequency of a ported box.

Fc or Fcb: The system resonance frequency of a driver in a sealed box. The system resonance frequency of a driver in a sealed box.

Feedback (Electronic) The return of a portion of the output of a circuit to its input. (Acoustic) A squeal of a sound system caused by the regeneration of a signal from the output of a sound system into a microphone input.

Filter An electrical or electronic device that permits certain frequencies to pass while obstructing others. Examples include loudspeaker crossovers, equalizers, feedback reducers and even simple bass and treble controls.
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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.

Flutter Echo A multiple echo in which the reflections occur in rapid succession caused by large surfaces being acoustically parallel to each other.

FOH Front of house with the audience as opposed to backstage.

Free Air Resonance: The natural resonant frequency of a driver when operating outside an enclosure.

Frequency The number of vibrations or oscillations in units per second. Measured in cycles or Hertz per second. The rate of repetition in cycles per second (Hertz) of musical pitch as well as of electrical signals. For example, the number of waves per second a vibrating device such as a piano or violin string moves back and forth each second of time to produce a musical note.

Frequency Response A measure of the effectiveness with which a circuit, device or system transmits the different frequencies applied to it. The way in which an electronic device (mic, amp or speaker) responds to signals having a varying frequency. This is a measurement of how well an amplifier reproduces and amplifies a specified audible range with equal amplitude or intensity, for example, 30 to 16,000 Hz.

Full Range The entire audio spectrum, 20 Hz - 20 kHz.

Fundamental: The lowest frequency of a note in a complex waveform or chord.

G

Gain An increase in strength or amplitude (voltage) in a signal. The increase in signal power that is produced by an amplifier; usually given as the ratio of output to input voltage, current, or power expressed in decibels.
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.
Ground Loop Hum caused by return currents or magnetic fields from relatively high-powered circuits or components which generate unwanted, noisy signals in the common return of relatively low-level signal circuits. A potentially detrimental loop formed when two or more points in an audio system that are nominally at ground potential are connected by a conducting path.
H
Haas effect: If sounds arrive from several sources, the ears and brain will identify only the nearest. In other words, if our ears receive similar sounds coming from various sources, the brain will latch onto the sound that arrives first. If the time difference is up to 50 milliseconds, the early arrival sound can dominate the later arrival sound, even if the later arrival is as much as 10 dB louder. The discovery of this effect is attributed to Halmut Haas in 1949.
Harmonics: Also called overtones, these are vibrations at frequencies that are multiples of the fundamental. Harmonics extend without limit beyond the audible range. They are characterized as even-order and odd-order harmonics. A second-order harmonic is two times the frequency of the fundamental; a third order is three times the fundamental; a fourth order is four times the fundamental; and so forth..
Headroom: The ability of an amp to go beyond its rated power for short durations in order to reproduce musical peaks without distortion. This capability is often dependent on the power supply used in the design.
Hearing The human hearing system is very well designed. It has a dynamic range of over 120 dB. Contemporary digital recording techniques can only achieve a dynamic range of about 90 dB. The typical threshold of pain is around 140 dB, with discomfort starting around a sound level of 118 dB. The normal hearing range is considered to be 15 Hz to 20 kHz. The typical Hi-Fi specification range is 20 Hz to 20 kHz. Typically, however, the average person cannot hear 20Hz. Sound reinforcement specifications reflect 50 Hz to 15 kHz (sometimes 40 Hz). Interestingly enough, this just happens to be the FCC limits on FM radio. The typical telephone has a frequency response of 400 Hz to 4 kHz. The human ear does not hear all frequencies at the same intensity. It's less sensitive at both the lower and upper ends of the frequency spectrum, and this characteristic varies with both age and sex. The amount of sensitivity is also a function of sound pressure level. The greatest intensity variations occur at very low sound pressure levels. The curve is relatively flat at sound pressures of 90 dB or so (Fletcher-Munson). The decibel is used in acoustic measurements because the human ear responds to the intensity of sound in approximately a logarithmic manner.
Sensitivity: Only 5% of people can hear a 1 dB difference in level (60 dB, 1 kHz); about 50% of people can hear a 2 dB change; and almost everyone can hear a 3 dB change. This means that when looking at equipment specifications, 1 dB frequency response specs are good; 3 dB specs are fair.

Relative level: 50% of people say about a 7.5 dB increase in level seems twice as loud . . . some as low as 5 dB, and some as high as 10 dB. This test is very level and frequency sensitive. Higher sound levels produce lower numbers and frequencies below 1 kHz and above 5 kHz yield higher numbers. The rule of thumb is 10dB. Applied to sound systems, to achieve output levels that appear to be twice as loud the system must produce over eight times more output power!
Hertz (Hz): A unit of measurement denoting frequency, originally measured as Cycles Per Second, (CPS): 20 Hz = 20 CPS. Kilohertz (kHz) are hertz measured in multiples of 1,000.
High-Pass Filter: A circuit that allows high frequencies to pass but rolls off the low frequencies. When adding a subwoofer it is often desirable to roll-off the low frequencies to the main amplifiers and speakers. This will allow the main speakers to play louder with less distortion. High-pass filters used at speaker level are usually not very effective unless properly designed for a specific main speaker (see impedance below).
High Z or High Impedance Any resistance to AC voltage or current generally greater than 2,000 Ohms.
Hiss: Audio noise that sounds like air escaping from a tire.
Hum: Audio electronic noise that has a steady low frequency noise.
I
Imaging: Listening term. A good stereo system can provide a stereo image that has width, depth and height. The best imaging systems will define a nearly holographic re-creation of the original sound
Impedance: Impedance is a measure of electrical resistance specified in ohms. Speakers are commonly listed as 4 or 8 ohms but speakers are reactive devices and a nominal 8-ohm speaker might measure from below 4 ohms to 60 or more ohms over its frequency range. This varying impedance curve is different for each speaker model and makes it impossible to design a really effective "generic" speaker level high-pass filter. Active devices like amplifiers typically have input impedance between about 10,000-100,000 ohms and the impedance is the same regardless of frequency.
Impedance Match The condition in which the external impedance of a connected load is equal to the internal impedance of the source, thereby giving maximum transfer of energy from source to load, minimum reflection, and minimum distortion.
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.
Infinite Baffle: A baffle 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 Overload Distortion produced by too strong a signal from the output of a microphone or other signal source connected to the input of a preamplifier.
Interconnects: Cables that are used to connect components at a low signal level. Examples include CD player to receiver, pre-amplifier to amplifier, etc. Most interconnects use a shielded construction to prevent interference. Most audio interconnects use RCA connections although balanced interconnects use XLR connections.
J
Jack A receptacle on a receiver, tape recorder, amplifier or other component into which a mating connector can be plugged.
Jitter: A tendency towards lack of synchronization caused by electrical changes. Technically the unexpected (and unwanted) phase shift of digital pulses over a transmission medium. A discrepancy between when a digital edge transition is supposed to occur and when it actually does occur - think of it as nervous digital, or maybe a digital analogy to wow and flutter.
K
Kevlar: Material developed by Dupont that is has an exceptional strength to weight ratio. Used extensively in bullet-proof vests, skis, sailboat hulls, etc. In audio, used in many variations for speaker cones.
Kilohertz (kHz): One thousand hertz. Its wavelength is approximately 13.56 inches long
L
Limiter An electronic circuit used to prevent the amplitude of an electronic waveform from exceeding a specified preset level while maintaining the shape of the waveform at amplitudes less than the preset level.
Linear Having an output that varies in direct proportion to the input.
Line Level: CD players, VCRs, Laserdisc Players etc., are connected in a system at line level; usually with shielded RCA type interconnects. Line level is before power amplification. In a system with separate pre-amp and power-amp the pre-amp output is line level. Many surround sound decoders and receivers have line level outputs as well.
Line Out An output connection found on mixers, preamps, tape decks, etc. providing an output at a level sufficient to drive the input of a power amplifier.
Line-Source: as in line array A speaker device that is long and tall. Imagine a narrow dowel dropped flat onto the water's surface. The line-source has very limited vertical dispersion, but excellent horizontal dispersion.
Lobing: Any time more than one speaker device covers the same part of the frequency range there will be some unevenness in the output. (Picture the waves from one pebble dropped into a calm pool vs. two pebbles dropped several inches apart.) Lobing means that the primary radiation pattern(s) is at some angle above or below the centerline between the two drivers. Good crossover design takes this into account.
Low Frequency Extension: Manufacturers, writers and salespeople toss around all kinds of numbers and terminology that can be very confusing and misleading. Good bass reproduction requires moving a lot of air and playback at realistic volumes. Remember the rule of needing to move four times the air to go down one octave. Example: You have a pair of good quality tower speakers with 10" woofers that produce good bass down to around 40Hz. The salesman is telling you that his little subwoofer with a single 10" woofer will extend your system down to 20Hz. If you've been paying attention, you know that this woofer will have to move eight times as much air as each of your 10" woofers, not likely. Adding that subwoofer to your system might give you more apparent bass energy, and in fact may help a little with movie special effects, but it is unlikely to extend bass response significantly. To extend the low frequency a dedicated driver is needed for the job available in 12-24 inch drivers but you will need deep pockets.
Low-Pass Filter: A circuit that allows low frequencies to pass but rolls off the high frequencies. Most subwoofers have low-pass filters built in and many surround sound decoders have subwoofer outputs that have been low-pass filtered.
Loudness: Perceived volume. Loudness can be deceiving. For example, adding distortion will make a given volume level seems louder than it actually is.
Low Z or Low Impedance Any resistance to AC voltage or current flow generally less than 2000 Ohms.
M
Magnetic-Planar Speakers: A type of speaker that uses a flat diaphragm with a voice coil etched or bonded to it to radiate sound. If the magnets are both in front of and behind the diaphragm, it becomes a push-pull magnetic-planar.
Master Main level or gain control for a device, bus or mixer.
Maximum power rating: A meaningless specification.
Microphone A microphone is a transducer that changes acoustical energy (sound) into electrical energy.
Midbass: Mid frequency bass, usually frequencies just above the sub-bass range, from around 100 - 400 Hz or so.
Midrange: A speaker, (driver), used to reproduce the middle range of frequencies. A midrange is combined with a woofer for low frequencies and a tweeter for high frequencies to form a complete, full-range system.
Mixer A device in sound reinforcement that has two or more signal inputs and a common signal output. Used to combine separate audio signals in desired proportions to produce an output audio signal.
Mode Another word for room resonance. When sound energy is restricted by boundaries (such as walls, floor, and ceiling) waves are developed at certain frequencies or wavelengths that are integers of the distance between the room boundaries. Room modes or resonance's cause standing waves because once the wave is generated it stands there, i.e., the positive pressure peaks (anti-nodes) and negative pressure troughs (nodes) stay stationary within the boundaries.
Monitor A loudspeaker or system of loudspeakers that permits the performer to evaluate or monitor his sound alone or in conjunction with other sounds that may be desired and is mixed to the listeners preference by means of a separate monitor or reference mix.
Mono Monophonic Sound - Sound produced by a system in which one or more microphones feed a single signal to an amplifier(s) whose output is coupled to one or more loudspeakers
Monopole: Any speaker that encloses the backwave of the speaker device even though part of this backwave may be released via. a port or duct. The primary radiation at most frequencies will be from the driver front. If the driver is not enclosed it becomes a dipole.
Muddy: Listening term. A sound that is poorly defined, sloppy or vague. For example, a "muddy" bass is often boomy with all the notes tending to run together.
Multicore A multiconductor shielded input cable which allows a number of signals between the stage and front of house mixer.The signal paths can go both ways from stage to desk (mics D.I. ect) and desk to stage (FOH mix monitor mixes) also known as Snakes
Muting: A way of blocking the signal path often used on mixers to stop sound from microphones etc. when not in use for example when backing singers mics are not in use
N
Neodymium magnet a permanent magnet that is lightweight and is currently the strongest type of permanent magnet used in certain speakers and microphones.
Noise Any extraneous sound or signal that intrudes into the original as a result of environmental noise, distortion, hum, or defective parts in the equipment.
Notch Filter A band rejection filter that produces a sharp notch in the frequency response of a system, thus reducing the gain or amplitude of a narrow band of frequencies centered on a given frequency.
O
Octave: An octave is a doubling or halving of frequency. 20Hz-40Hz is often considered the bottom octave. Each octave you add on the bottom requires that your speakers move four times as much air!
Ohm: A unit of electrical resistance or impedance. speakers are often rated between 4-16 ohms in order to match them with amplifiers.
Omnidirectional A term usually applied to microphones to refer to uniform pickup of sound from all directions.
Out of Phase: When 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. The power (usually in watts but sometimes volts) delivered by an amplifier
Output Impedance The internal output impedance of an amplifier presented by the amplifier to the load. (not to be confused with load impedance.)
Output Power The power delivered by a system to its load. (i.e. an amplifier driving a loudspeaker system)

Overload: A condition in which a system is given too high of an input level. A common cause of distortion or product failure.
Overtones: See Harmonics.

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).

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.
Push-pull: Most common type of amplification that amplifies the negative and positive sides of the waveform separately. Allows for much higher power output than single-ended.
Q
Q The directivity factor of a transducer (loudspeaker) used for sound emission. The higher the value of Q the more directional the speaker.
Quantizing in digital and midi recording a way of correcting the timing of notes for example if a note is played late, after the beat, or early, before the beat quantization will correct these errors the danger is if all the notes are qantized that the music will sound sterile and mechanical.
R
Radio-frequency interference (RFI): Radio-frequency sound waves can be caused by many sources including; mobile phones, short-wave radio equipment, household electrical line, computers and many other electronic devices. RFI sometimes interferes with audio signals, causing noise and other distortions.
RCA Connector: "Phono" plugs, used primarily as low-level connections between Phonographs/CD players/Tuners/Recievers/Amplifiers
Real Time Analyzer (RTA) An electronic instrument used to measure the combined response of an audio system and the room in which the system is operating.
Receiver: A radio device that decodes a radio signal from a radio mic or guitar belt pack.
Reference Levels
O dB
In the measurement of SPL or Sound Pressure Level, 0 dB is referenced to the threshold of hearing or auditory perception of a tone of 1000 cycles (hertz) per second (1 kHz). 0 dB must always be referenced to some base of measurement. In gain functions 0 dB is unity gain (1).
3 dB
The amount of SPL gained by doubling the power to a speaker. Also the amount gained by doubling the number of speakers.
+/- 3 dB
Plus or minus 3 dB as used to express a measurement of frequency response indicates that the response will be no more than +3 dB and no less than -3 dB below a given reference. It is actually a 6 dB window. The Response of 60 Hz to 14 kHz +/-3 dB means that within the bandwidth of sixty cycles per second to fourteen thousand cycles per second, no frequency is +3 dB more nor -3 dB less than a specified reference frequency.
3 dB DOWN (-3 dB)
The point at which a measured power level is 3 dB below the specified level. In an electronic crossover, the point (frequency) at which the high pass signal is -3 dB down in response or power level is considered the crossover point (frequency).
-6 dB
The amount of loss in SPL as you double the distance away from a sound source.
dBm
A decibel scale referenced to 0 dBm = 1 milliwatt of power into 600 Ohms or .775 volts RMS across 600 ohms.
dBu
Primarily a British term for gain referenced to 0 dBu = .775 volts RMS.
dBV
A decibel scale referenced to 1 volt RMS; 0 dBV = 1 volt.
dBW
A term for power gain referenced to 0 dBW = 1 Watt.
Reflection The bouncing back or return of sound waves from walls or other obstacles which they strike.
Refraction A change in direction or bending of the propagation of a sound wave when it passes from one medium to another in which the velocity of sound is different.
Regeneration In audio, regeneration is another word for feedback; when something regenerates it continues or sustains itself as an oscillation. When an electronics engineer designs an oscillator, he takes the output of a gain stage and feeds it back into the input through a tank circuit (an RC, resistor and capacitor or an LC, inductor and capacitor combination); when the circuit is turned on it begins to regenerate or oscillate at a specific frequency determined by the value of the RC or LC combination. When the output of a loudspeaker in a sound reinforcement system is able to get back into a microphone or sound system input, at some level and resonant frequency, the system is going to go into regeneration or feedback oscillation (squeal).
Resistance (Re): In electrical or electronic circuits, a characteristic of a material that opposes the flow of electrons. Speakers have resistance that opposes current.
Response The range of frequencies to which an amplifier or speaker will respond, and the relative amplitude or intensity with which these frequencies are reproduced
Resonant frequency: At that frequency, even a slight amount of energy can cause the system to vibrate. For example cars passing a window all day then a bus or lorry passes and the window shakes and rattles. A stretched piano string, when plucked, will vibrate for a while at a certain fundamental frequency. Plucked again, it will again vibrate at that same frequency. This is its natural or resonant frequency. While this is the basis of musical instruments, it is undesirable in music-reproducing instruments like audio equipment.
Return An input, typically found on a mixing console, used to patch a signal returning to a particular BUS after having been further processed, such as an echo or effects return.
Reverb (Reverberation, acoustical)
The prolongation of sound at a given point after direct sound from the source has ceased, due to such causes as reflection from physical boundaries. (Electro-mechanical) An electro-mechanical device usually employing springs which randomly reflect as great amount of sound as possible, therefore simulating natural reverberation. (Digital Reverb) An electronic reverberation effects processor that uses digital electronics to introduce the multiple delay paths.
Reverberation The sustaining of acoustical energy in a room after the reception of the direct field (the sound coming directly from the source) ceases in producing sound. Reverberation is caused by the reflections and scattering of sound energy from the boundary surfaces of the room.
Ribbon Speaker: A type of speaker that uses a pleated conductor suspended between magnets. Most true ribbons are tweeters only. Sometimes confused with magnetic-planar speakers.
Ring Mode A tone or frequency sounded in a room with a live sound reinforcement system prior to the system breaking into feedback. A ring mode lies just below the threshold of feedback.
RMS (root-mean-square): The square root of the mean of the sum of the squares. Commonly used as the effective value of measuring a sine wave's electrical power. A standard in amplifier measurements.
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

Satellite: A satellite speaker is usually fairly small, and does not reproduce the lowest frequencies. Usually meant to be used with a woofer or subwoofer.
Sealed enclosure: An airtight enclosure that completely isolates the back wave of the driver from the front. Very tight, defined sound
Send An output used to patch a signal from a channel or bus of a mixer to an external signal processor such as an echo or digital delay.
Sensitivity: A measurement of how much power is required for a loudspeaker to achieve a certain output level. The general standard used is on-axis SPL (Sound Pressure Level) at 1-watt input, 1-meter distance.
Shelving A type of equalization circuit that has a shelf-like characteristic at the upper or lower ends of the spectrum. A shelving EQ at 15 kHz, in the boost position, would increase the high frequencies up to 15 kHz where it would shelf.
Signal-to-noise (SN) Ratio: The range or distance between the noise floor (the noise level of the equipment itself) and the music signal.
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-ended: Type of amplification often, (but not always), using vacuum tubes. Typically low power output, low damping factor and relatively high distortion. Single-ended enthusiasts claim that the sound quality is more "real".
Slapback Echo A echo caused from reflections off the rear wall in many auditoriums. Such echo can reduce the intelligibility of a sound reinforcement system, as well as distract speakers and performers on stage. Severe slapback echo is very distracting for a musician, as it can cause confusion that makes following that beat in time extremely difficult. A professional high quality stage monitor system can mask some of the slapback echo to a certain extent by providing more direct sound from the monitor speaker in the first 25 milliseconds which the performer perceives through auditory fusion as more direct field, thus increasing the ratio of the level of the direct field to that of the slapback echo.
Slew Limiting The failure of the amplifier's output to move as fast, voltage-wise, as the input would have it move.
Slew Rate Refers to the ability of an amplifier's output to accurately reflect the input waveforms' rise time transients. An amplifier is said to have a slew rate of so many volts per microsecond. A slew rate of 20 volts per microsecond (20 V/U sec.) means that the amplifier is capable of swinging 20 volts positive or negative in the period of one microsecond.
Snake see multicore.
Sound A pressure wave motion propagated in an elastic medium (air) producing an auditory sensation in the ear by the change of pressure at the ear. Sound waves are produced by a vibrating body in contact with air.
Sound Level Meter The instrument used to measure noise and sound pressure levels (SPL), calibrated in decibels.
Sound Fields
Direct Field
The sound that emanates directly from a sound source or loudspeaker.
Indirect Field
That sound perceived from behind a speaker system, i.e. when no direct field is present.
Near Direct Field
The sound field that is generated close to the source or loudspeaker. Generally considered that sound field that is within a distance from the source of less than two wavelengths.
Far Direct Field
The sound field that is perceived at a distance from the source loudspeaker that is greater than 2 wave lengths.
Free Field
That portion of the direct field of a sound source or loudspeaker that is reflection free or not yet affected by boundaries such as walls or ceiling (such as may be encountered with an outdoor sound system).
Reverberant Field
That sound field beyond critical distance where most of the energy arriving at the listener is in the form of reflected energy off the room's boundaries.
Spectrum Refers to a particular band of frequencies. The normal acoustic sound spectrum is the range of human auditory perception (20 Hz to 20,000 Hz). There is also a Subsonic spectrum (considered to be below about 40 Hz) and an Ultrasonic audio spectrum (above 20,000 Hz).
Spectrum Analyzer [See Real Time Analyzer (RTA)]
Sound Pressure Level (Spl): Given in decibels (DB) is an expression of loudness or volume. A 10db increase in SPL represents a doubling in volume. Live orchestral music reaches brief peaks in the 105db range and live rock easily goes over 120db.
Sound Waves: Sound waves can be thought of like the waves in water. Frequency determines the length of the waves; amplitude or volume determines the height of the waves. At 20Hz, the wavelength is 56 feet long! These long waves give bass its penetrating ability, (why you can hear boy racers coming before you can see them)
Splitter A box, which has one microphone or signal input and has two or more individual outputs available for that signal. Used to connect one signal source to multiple other devices.
Standing wave: A build-up 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 seashell.
Stereo: From the Greek meaning solid. The purpose of stereo is not to give you separate right and left channels, but to provide the illusion of a three-dimensional, holographic image between the speakers.
Sub-Master A separate mixing bus assigned to a group of mixing channels that enables the sound mixer to regulate the level of that group with one control called the Sub-Master.
Sub-Mix A level control preceding the main (master) level control, that regulates the level of an individual sub-mix.
Subwoofer: A speaker designed exclusively for low-frequency reproduction. A true subwoofer should be able to at least reach into the bottom octave (20-40Hz). There are many "subwoofers" on the market that would be more accurately termed "woofers".
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.
Switching Jack An input or output jack that performs some switching function in addition to providing an input or output for a signal. These jacks disconnect the normal flow of signal and allow for additional patching capabilities such as inserting equalizers and feedback reducers. Most typically these are 1/4" phone jacks, but some equipment manufacturers are now using switching RCA type phono connectors.
T
Thiele/Small parameters: The numbers that specify the behaviour of drivers, as defined and analysed by two engineers, Neville Thiele and Richard Small.
Timbre: The quality of a sound that distinguishes it from other sounds of the same pitch and volume. The distinctive tone of an instrument or a singing voice.
Timbral: Refers to the overall frequency balance of a system. In a perfect world, all systems would have complete tonal neutrality. With current technology, this ideal is approached but not met. Listening to many equally "good" speakers will reveal that some sound warmer than others, some sound brighter etc. In a surround sound system it is important that all speakers have a close timbral match for the highest degree of sonic realism.
Total harmonic distortion (THD): Refers to a device adding harmonics that were not in the original signal. For example: a device that is fed a 20Hz sine wave that is also putting out 40Hz, 80Hz etc. Not usually a factor in most modern electronics, but still a significant design problem in loudspeakers.
Transducer: A device that converts one form of energy to another. Playback transducers are the phono cartridge, which changes mechanical vibrations into electrical energy, and the loudspeakers, which change it back, from electrical energy coming from the amp to mechanical movement of the diaphragm, causing audible pressure changes in the air.
Transmission Line: Also referred to as a T-line. A type of bass cabinet in which the back wave follows a relatively long, usually damped path before being ported to the outside. T-lines are usually rather large and costly cabinets to manufacture. Opinions vary widely over the "best" type of bass cabinet, but much has to do with how well a given design, such as a transmission line is implemented.
Transient response: The ability of a component to respond quickly and accurately to transients. Transient response affects reproduction of the attack and decay characteristics of a sound.
Transparency: Listening term. An analogue that can be best "pictured" in photography. The more "transparent" the sound, the clearer the auditory picture.
Transients: Instantaneous changes in dynamics, producing steep wave fronts.
Tri-Amp Separating the audio spectrum into three bands, i.e., high frequencies, mid-band frequencies and low frequencies by means of an electronic crossover and using three separate power amplifiers to amplify the three outputs of the crossover (high pass, mid pass, low pass outputs) driving three separate components of a speaker system; resulting in increased headroom and dynamic range.
triaxial driver. A speaker with three magnet assemblies all in line with each other's centre. The outer cone is the bass element with its own coil and magnet inside that a mid range cone with its own coil and magnet and inside that on the centre axis a tweeter or horn element. This is primarily intended for stage monitors tri-amped from a three way active crossover

Tri-wiring: The use of three pairs of speaker wire from the same amplifier to separate bass, midrange and treble inputs on the speakers.
Tweeter: A speaker, (driver), used to reproduce the higher range of frequencies. To form a full-range system, a tweeter needs to be combined with a woofer, (2-way system), or a woofer and midrange, (3-way system).
U
Unbalanced Cable or Line A single conductor cable with a surrounding shield that connects to ground. Such a system is called unbalanced because it cannot be balanced or offer common mode rejection.
Unbalanced Input An input in which one of the two terminals is at ground potential or connected to the chassis ground.
Unidirectional This term commonly refers to microphones which pickup sounds predominately from one direction as opposed to all directions (omnidirectional). Unidirectional microphone types include cardioid, super-cardioid and hyper-cardioid. Unidirectional microphones are most often used in sound reinforcement applications because they are generally less prone to feedback than omnidirectional types.
Unity gain: A circuit with unity gain will not increase or decrease the volume level.
V
Velocity In audio the velocity or speed of sound is approximately 1125 feet per second. The speed of sound changes slightly with changes in temperature, humidity, and altitude.
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): The unit of measurement used to measure how much "pressure" is us Volume
The intensity or loudness of sound.
Volume The intensity or loudness of sound.
VU (volume unit) A unit for expressing the audio frequency power level of a complex electronic waveform such as that corresponding to speech or music. 0 VU is referenced to 1 milliwatt of power.
VU Mete A meter than indicates the audio frequency power level or volume units of a complex electronic waveform.

W

Warmth: A listening term. The opposite of cool or cold. In terms of frequency, generally considered the range from approx. 150Hz-400Hz. A system with the "proper" warmth will sound natural within this range.
Wattage: Is the unit of power used to rate the output of audio amplifiers. For a wattage number to have meaning the distortion level and impedance must also be specified.
Wavelength: The distance the sound wave travels to complete one cycle. The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency. (Speed of sound at sea level is 343 meters/second or 1,125 feet/second).
Woofer: A speaker, (driver), used for low-frequency reproduction. Usually larger and heavier than a midrange or tweeter.
X

XLR: A type of connector used for balanced lines. Used for microphones, balanced audio components and the AES/EBU digital connection.
Y
Y-Adapter: Any type of connection that splits a signal into two parts. An example would be a connector with one male RCA jack on one end, and two female RCA jacks on the other end.
Z
Zobel Filter: A series circuit consisting of a resistance and capacitance. This filter is placed in parallel with a speaker driver to flatten what would otherwise be a rising impedance with frequency.