Reference of Sound Reinforcement Terms
A
A-B Test
Evaluating comparative performance of two or more models of equipment such as amplifiers or speaker systems by listening and switching quickly from one to the other. It is possible to connect an A-B Test to any two pieces of the same type of equipment from anywhere in the audio chain.
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. Certain materials, such as acoustical ceilings, may absorb more high frequencies than lows. Diaphragmatic absorption, caused by loose wall panels or cavities behind panels, can cause certain low frequencies to be absorbed.
AC Mains
110-120 volts alternating current (60 Hz), which is what you plug your power cord into.
Acoustic
Relating to, containing, producing, arising from, actuated by, or carrying sound. 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.
Active
A type of electronic circuitry that can increase the gain or amplitude of a signal. Examples include active gain controls, active equalization, active direct boxes, and active crossovers.
Ampere
Named after André Ampère (1775-1836), a French scientist. A unit of measurement of electrical current (I). One amp of current represents 6.28 × 1018 electrons flowing past a given point in one second, and is equal to one coulomb.
Amplifier (AMPL)
A device capable of increasing the gain (magnitude) or power level of a voltage or current that is varying with time (frequency), without distorting the waveform of the signal. The amplifier is, just as the word implies, a signal amplifier. The incoming signal from any program material source is far too weak to power a speaker system. The role of the amplifier is to take that weak signal and strengthen it to the necessary power level to operate the loudspeakers with minimal distortion.
Analog
A physical variable which remains similar to another variable insofar as the proportional relationships are the same over some specified range. The electrical signal produced by a microphone is an electrical analog of the acoustic sound that the microphone is reproducing. The continuous electrical signal that the microphone produces varies in voltage and frequency as a direct correlation to the nonelectrical acoustic information impressed on the transducer.
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, resulting in 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.
Attenuation
The reduction in level of a signal.
Audio Chain
The order or sequence for connecting audio components, such as microphone, preamplifier (mixer), effects device, graphic equalizer, crossover, amplifier, and speaker.
Audio Range
20 Hz to 20,000 Hz (twenty cycles per second to twenty thousand cycles per second). The frequency response spectrum of human auditory perception.
Aux Input
An auxiliary input that serves as a straight connection to a signal bus. For instance, a monitor Aux input is an Aux input to the monitor bus.
B
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.
Balanced Cable
A pair of wires surrounded by a braided shield.
Balanced Line
A transmission line consisting of two conductors plus a braided shield, capable of being operated so that the voltages of the two conductors are equal in magnitude and opposite in polarity with respect to ground. A balanced line offers common-mode rejection or cancellation by attenuation of signals electromagnetically induced into the signal lines.
Bandpass
Refers to a type of filter that passes a certain band of frequencies uniformly and attenuates, or reduces, the level of frequencies below and above the specified bandpass.
Bandwidth
A response characteristic in which a definite band of frequencies, having a low-frequency and high-frequency limit, are transmitted or amplified uniformly.
Bass Reflex
A type of speaker enclosure in which the speaker's rear sound wave emerges from a critically dimensioned auxiliary opening or port to reinforce the bass tones.
Biamp
Separating the audio spectrum into two bands, high frequencies (high pass) and low frequencies (low pass), by means of an electronic crossover and using two separate amplifiers or channels of an amplifier. One amp or channel is used to amplify and project the high-pass signals from the high-frequency component or horn of the speaker system, while the other amp or channel amplifies the low-pass signals and projects them from the woofer or low-frequency component. This results in increased headroom and dynamic range.
Boost
A term used to indicate an increase in gain of a frequency or band of frequencies when equalizing an audio signal. Opposite of cut.
Bridge Mode (Mono)
Operating a stereo amplifier in mono via the bridge mode switch, which then makes Channel A output the positive power rail and Channel B output the negative power rail. Since the signal swings between A and B channels, the output of the amplifier is twice that of single-channel operation.
Bridging
Connecting one electrical circuit in parallel with another. Example: paralleling power amplifier inputs.
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.
C
Capacitor
A device which consists essentially of two conductors, such as parallel metal plates, insulated from each other by a dielectric. It introduces capacitance into a circuit, stores electrical energy, blocks the flow of direct current (DC), and permits the flow of alternating current (AC) to a degree dependent on the capacitor's capacitance and the current frequency.
Cardioid
A type of microphone having a heart-shaped pickup pattern that picks up sound better from the front (on axis) than the back (off axis).
Clipping
Amplifier overload causing a squaring off or undesirable change in the waveform, resulting in distortion or perceptible mutilation of audio signals.
Cluster
An array of loudspeakers or horns suspended above an audience to act as a single or point source of sound.
Coincident
Two signals are said to be coincident when they correspond exactly, fall upon or meet at the same point, coinciding or occurring in space or time in exact agreement.
Comb Filter
When two combining sound waves have different amplitudes, phases, and frequencies, the resultant sound wave 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.
Combining
A combining filter is a filter that will combine with another filter, with the total response being a combination of the two filters.
Common Mode Rejection
The ability of an amplifier to cancel a common-mode signal, such as interference, that is applied equally to both ungrounded inputs of a balanced amplifier, while responding to a signal from the source that is constantly changing direction (alternating current). It is out of phase with respect to the two balanced signal lines; therefore, it is not common mode and will be passed rather than rejected.
Compression
Reduction of the effective gain of an amplifier at one level of signal with respect to the gain at a lower signal level.
Conductor
A wire, cable, or other material such as metal, liquids, gases, or plasma that is suitable for carrying electric current.
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 1,000 Hz for a specific distortion. Continuous power in watts: W = V2/R.
Continuous Program Material
A signal, such as speech or music, that contains voltages continuously changing in both frequency and voltage (time and amplitude).
Contour
The tone circuit in a Peavey reverb amplifier. Contour also applies to bass boost used to attain equal loudness at lower volumes.
CPS
Abbreviation for "cycles per second," the units for expressing frequency. The term CPS is obsolete and has been replaced by Hertz. Hertz = cycles per second. 1 kHz = 1 kc.
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 (X-Over)
An electronic device that is used to separate an audio signal into two or more bands of frequencies or component signals above and below a certain frequency, called the crossover frequency or crossover point. Crossovers can be active or passive.
Crossover Passive
A passive crossover is built into most speaker cabinets in order to separate bands of frequencies from the full-range speaker-level signal produced by the power amplifier and route those bands of frequencies to the proper speaker or driver.
Crossover Active
Electronic or active crossovers do not have the problem of excess power because only the power needed by the driver must be generated by the amplifier. An active crossover is employed when biamping a system. It separates the full-range audio spectrum into bands of frequencies above (high pass) and below (low pass) a certain frequency.
Crosstalk
Interaction of adjoining channels or circuits. Crosstalk can occur by being induced electromagnetically or electrostatically. Crosstalk is a common specification for mixing consoles.
Current
The rate of flow, measured in amperes, of electricity in a conductor or circuit. The amount of current that flows is determined by the voltage or electrical pressure applied and the conductivity of the substance or material, which also determines the resistance or opposition to current flow.
Cut
A term used to indicate the reduction in gain or attenuation of a frequency or band of frequencies when equalizing an audio signal.
Cycle or Hertz
A unit of motion referenced to a time period of one second. The frequency of a vibration or oscillation in units per second. One hundred Hertz or 100 CPS refers to the number of times per second a string is vibrated or an amplifier swings between its positive and negative supply voltage.
D
Damping Factor
The ratio of the speaker impedance to the amplifier's internal output impedance. Damping factor is a measure of how well an amplifier can control the movement of a speaker cone or diaphragm by preventing it from moving farther than it is supposed to. Damping factor is arrived at by dividing the speaker impedance by the amplifier's internal output impedance. Anything connected in the speaker line, including the speaker cable itself or a crossover, looks to the speaker like an increase in the output impedance of the amplifier, thus lowering the effective damping factor.
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.
0 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 1,000 Hz. Zero 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. It is also the approximate amount gained by doubling the number of speakers.
+/- 3 dB
Plus or minus 3 dB is a measurement of frequency response that exhibits no more than +3 dB and no less than -3 dB below a given reference. It is actually a 6 dB window. A response of 60 Hz to 14 kHz +/-3 dB means that within the bandwidth of 60 Hz to 14 kHz, no frequency is more than 3 dB above or 3 dB below the specified reference.
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 at which the high-pass signal is -3 dB down in response or power level is considered the crossover point.
-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 0.7746 volts RMS across 600 ohms.
dBu
Primarily a British term for gain referenced to 0 dBu = 0.7746 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.
The Decibel
Originally, the "bel," named in honor of Alexander Graham Bell, was the logarithmic term called the "transmission unit," which was used to express the transmission losses of long telephone lines. The bel was too large for practical use, so it was later changed to the decibel. The decibel has no actual numerical value, but is used to express a ratio between two voltages, currents, powers, or impedances.
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.
Diaphragmatic Absorption
Absorption of sound energy due to the flexing of wall panels at low frequencies. Wall panels mounted on a solid backing but separated from it by an air space can respond to impinging sound waves by vibrating. This results in absorption of sound energy due to frictional losses caused by the flexing of fibers in the wall panel.
Differential Amplifier
An amplifier whose output is proportional to the difference between the voltages applied to its two inputs. Used to balance or offer common-mode rejection of interference signals.
Diffraction
The bending or redistribution of acoustic sound waves in a room caused by an obstacle, such as a column or divider. Low-frequency waveforms are most affected by diffraction.
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 analog audio signal. In digital audio, the continuous analog 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.
Directivity
The area of coverage of a speaker or microphone.
Dispersion
The spread, distribution, or coverage of sound generated from a horn or loudspeaker. For any given frequency, the area of dispersion is defined as that area between the -6 dB points of that frequency plotted against amplitude. It is measured in degrees related to an imaginary line descending from the center of the speaker cone.
Distortion
Any undesired change in the waveform of an electrical signal passing through a circuit or transducer. Distortion can be defined as a deviation from the original sound. When reproducing sound, distortion is generally unwanted, although performers may intentionally use electronically induced distortion as a musical effect.
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.
Dynamic Range
In a musical instrument, dynamic range is the difference in decibels between the loudest and softest level of notes that can be played. In electronic equipment, it is the difference in decibels between the highest overload level and lowest acceptable level of a signal system or transducer.
E
Echo
A delay in sound of more than 50 milliseconds resulting in a distinct repeat or number of repeats of the original sound.
Efficiency
The ratio, usually expressed as a percentage, of the useful power output to the power input of a device.
Electronically Balanced Input
A differentially balanced amplifier whose output is proportional to the difference between the voltages applied to its two inputs. It offers common-mode rejection or attenuation of interference signals introduced electromagnetically into the signal-carrying conductors.
Enclosure
An acoustically designed housing or structure for a speaker.
Equalization
The act of obtaining a desired overall frequency response through the implementation of graphic equalizers or tone controls. The name equalization implies balance, for when you equalize you balance the audio spectrum.
Excursion
Movement of the cone of a loudspeaker or the diaphragm of a compression driver. The higher the voltage or amplitude of the signal applied, the greater the movement or excursion.
Exponential Horn
A speaker designed to reproduce high frequencies. An exponential horn has a flare rate that increases with the square of the distance from the entry to the horn throat.
F
Far Field
That portion of the direct field that is at least twice the distance of a frequency's wavelength.
Feedback
Electronic feedback is the return of a portion of the output of a circuit to its input. Acoustic feedback is the 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, such as a crossover filter used with loudspeakers.
Flutter Echo
A series of rapid, specific reflective returns of sound energy caused by large surfaces being acoustically parallel to each other.
Frequency
The number of vibrations or oscillations in units per second, measured in cycles or Hertz. It is the rate of repetition in cycles per second of musical pitch as well as electrical signals.
Frequency Response
A measure of the effectiveness with which a circuit, device, or system transmits different frequencies. It describes how an electronic device such as a microphone, amplifier, or speaker responds to signals having varying frequencies.
Full Range
The entire audio spectrum, approximately 20 Hz to 20 kHz.
G
Gain
An increase in strength or amplitude, usually voltage, in a signal. The increase in signal power produced by an amplifier is usually given as the ratio of output to input voltage, current, or power expressed in decibels.
Ground
A heavy cable connected to earth via a metal copper stake for the purpose of grounding electrical equipment. In the U.S., a third wire in the electrical system is connected to earth ground to provide a means of connecting the chassis of electrical equipment to earth ground and help provide protection against hazardous electrical shock.
Ground Loop
Hum caused by return currents or magnetic fields from relatively high-powered circuits or components that generate unwanted signals in the common return of relatively low-level signal circuits. A ground loop can form when two or more points in an audio system that are nominally at ground potential are connected by a conducting path.
H
Haas Effect
Refers to the condition of the human auditory system that permits a listener to merge information arriving within the first approximately 20 milliseconds as a single event. This is sometimes called the precedence effect.
Harmonic
One of a series of sounds, each having a frequency that is an integral multiple of some fundamental frequency.
Headroom
The difference between the average operating power level of an amplifier circuit and the point at which clipping or severe distortion occurs.
Hearing
The human hearing system has a dynamic range of more than 120 dB. The typical threshold of pain is around 140 dB, with discomfort beginning around 118 dB. The normal audible frequency range is often considered approximately 20 Hz to 20 kHz, although hearing varies significantly between individuals and with age.
Hertz (Hz)
A unit of measurement previously referred to as cycles per second, used to indicate the frequency of sound or an electrical wave. One Hertz represents one cycle per second.
High Pass
All signals above a given crossover frequency.
High Z or High Impedance
Any resistance to AC voltage or current generally greater than 2,000 ohms.
Hum
An electrical disturbance that can occur in sound equipment due to the frequency of the power distribution system or any number of its harmonics. In the U.S., power-line frequency is 60 Hz. Hum can occur at 60 Hz, 120 Hz, 180 Hz, 240 Hz, and so on.
I
IM (Intermodulation Distortion)
Nonlinear distortion characterized by the appearance of output frequencies equal to the sums and differences of integral multiples of the input frequency components. For example, an amplifier with high IM distortion amplifying 100 Hz and 2,000 Hz may also generate distortion components at 1,900 Hz and 2,100 Hz.
Impedance
The total opposition to alternating current flow presented by a circuit. It is the resistance to the flow of alternating current in an electrical circuit, generally categorized as either high or low, but always expressed in ohms.
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.
Impulse
A type of signal that switches on and off as opposed to remaining in a steady state like a continuous sine wave. Music is more impulsive in nature than it is steady state.
Inductance
That property of an electric circuit or of two neighboring circuits whereby an electromotive force is generated by electromagnetic induction in one circuit by a change in itself or in the other.
Inductor
A coil of wire used to create an impedance whose reactive component is low, therefore offering low resistance at low frequencies and high resistance at high frequencies. An inductor passes low frequencies and attenuates or rolls off high frequencies.
Infinite Baffle
A baffle that effectively prevents all of the loudspeaker's rear sound waves from interfering with its front waves.
Input Overload
Distortion produced by too strong a signal from the output of a microphone or another signal source, such as a keyboard, connected to the input of a preamplifier.
Insertion Loss
A loss in gain of a system after a component has been added or inserted into the system. Insertion loss is a loss of headroom.
Integrated
A type of design in which two or more basic components or functions are combined physically as well as electrically, usually on one chassis, as opposed to a separate mixer and power amplifier.
Intensity
The human ear is less sensitive at both the lower and upper ends of the frequency spectrum, and this characteristic varies with age and other factors. The amount of sensitivity is also a function of sound pressure level. The decibel is used in acoustic measurements because the human ear responds to the intensity of sound in approximately a logarithmic manner.
J
Jack
A receptacle on a receiver, tape recorder, amplifier, or other component into which a mating connector can be plugged.
K
Kilohertz
A frequency of one thousand cycles per second (1 kHz).
L
LED
Light-emitting diode, a semiconductor device that produces visible light when a voltage of a certain polarity and potential is applied to it.
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 below the preset level.
Linear
Having an output that varies in direct proportion to the input.
Linear Frequency Scale
A scale on which each equal-length division represents an equal number of Hertz. If you add the equal-length division in Hertz to the last division frequency, you get the next frequency in a series.
Line Out
An output connection found on mixers and preamps providing an output at a level sufficient to drive the input of a power amplifier. On some guitar amplifiers, the line output may provide a frequency-compensated signal.
Load Impedance
The actual impedance of the load or speaker that a power amplifier is connected to, thus driving a load of a certain impedance.
Logarithmic Frequency Scale
A scale on which each division represents an exponential constant. Each division from a reference point is proportional to its logarithm.
Loudness Control
A volume control with special circuitry added to compensate for the normal decreased hearing ability of the human ear at the extreme ends of the audio range when listening at lower sound levels. A typical loudness control boosts bass frequencies and, to a lesser extent, high frequencies.
Loudspeaker Efficiency
The ratio, expressed as a percentage, of signal output to signal input used to state the power needed to drive a loudspeaker. For example, a power output of 2 watts from a 10-watt input represents 20% efficiency.
Low Pass
All of the frequencies below a given crossover frequency.
Low Z or Low Impedance
Any resistance to AC voltage or current flow generally less than 2,000 ohms.
M
Master
Main level or gain control for a bus or mix.
Microphone
A microphone is a transducer that changes acoustical energy, or sound, into electrical energy.
Mixer
A device in sound reinforcement that has two or more signal inputs and a common signal output. It is used to combine separate audio signals linearly 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 related to the dimensions of the room. Room modes or resonances cause standing waves.
Monitor
A loudspeaker or system of loudspeakers that permits a performer to evaluate or monitor their sound alone or in conjunction with other sounds. The monitor mix can be controlled separately from the main mix.
Mono
Monophonic sound produced by a system in which one or more microphones feed a single signal-processing amplifier whose output is coupled to one or more loudspeakers.
Multimeter
Also called a Volt-Ohm-Meter (VOM). A measuring instrument that can measure different ranges of voltage, current, and resistance. A multimeter can have an analog needle indicator or a digital readout.
Music Power
A power rating generally applied to high-fidelity amplifiers for tones of short duration. It takes into account the fact that most amplifiers can produce greater power in short bursts than they can continuously. It is higher than continuous power ratings for the same amplifiers.
N
Noise
Any extraneous sound or signal that intrudes into the original as a result of environmental noise, distortion, hum, or defective equipment or components.
Notch Filter
A band-rejection filter that produces a sharp notch in the frequency response of a system, reducing the gain or amplitude of a narrow band of frequencies centered on a given frequency.
O
Octave
The interval between any two frequencies having a ratio of 2 to 1. For example, A 440 is an octave above A 220.
Ohm
The unit of electrical resistance, equal to the resistance through which a current of one ampere will flow when there is a potential difference of one volt across it.
Omnidirectional
Applied to microphones to refer to uniform pickup of sound from all directions.
Oscilloscope
A test instrument that shows a picture of electrical waveforms by means of a cathode ray tube or digital display. An oscilloscope is calibrated so one can measure instantaneous values and waveforms of electrical signals that change rapidly or vary as a function of voltage or time.
Output Impedance
The internal output impedance of an amplifier presented by the amplifier to the load. Output impedance is sometimes incorrectly used instead of load impedance.
Overtone Harmonic
Multiples of the frequency of a fundamental waveform.
P
Pad
A fixed passive network that reduces the electrical level of a signal. An attenuator.
Parallel
An electric circuit in which the elements or components are connected between two points, with one end of each component connected to each point.
Parametric
A type of equalization circuit that has three variable parameters: frequency, cut or boost, bandwidth, and Q.
Passive
An electronic circuit composed of passive elements such as resistors, inductors, or capacitors without active elements such as vacuum tubes or transistors, generally resulting in a signal loss.
Peak
The maximum instantaneous value of a signal amplitude.
Peaking
A term used to indicate an increase in gain of a frequency or band of frequencies when equalizing an audio signal.
Peak Power
Peak power is a power rating sometimes used by manufacturers that generally represents a short-duration maximum rather than continuous amplifier performance. Amplifier power should be compared using consistent, meaningful specifications such as continuous power.
Peak-to-Peak
Amplitude of an alternating voltage measured from negative peak to positive peak.
PFL
Pre Fade Listen. A button that permits a channel or sub to be monitored before that channel or sub's level control or fader.
Phase
Phase is the time relationship between two related events. Two signals are in phase when they reproduce the same sound or signal simultaneously. They are out of phase to the extent that one leads or lags behind the other in time.
Phase Cancellation
Signals that are out of phase will cancel one another according to the difference in phase in degrees. A transducer, such as a speaker or microphone, wired out of phase with another can result in reduced combined output due to phase cancellation.
Piezo-Electric
Having the ability to generate a voltage when mechanical force is applied, or to produce a mechanical force when a voltage is applied, as in a piezo-electric crystal.
Point Source
A source of acoustic sound waves having a definite position but no extension into space. A point source is an ideal, imaginary single point in space. A cluster or array of horns and loudspeakers can be positioned using this imaginary point as a reference.
Polarity
The quality of having opposite poles. In electromagnetic and electrical systems, polarity refers to opposite electrical potentials or magnetic poles.
Post
On a mixer, post means that a function is derived after the channel slider or gain control.
Power
Electrical energy, measured in watts, such as the current from an amplifier used to drive a loudspeaker. Power in watts: W = V2/R.
Power Amplifier
The final active stage of the audio chain, designed to deliver maximum power to the load or speaker impedance for a given percentage of distortion.
Pre
On a mixer, pre means before. For example, a pre-fade monitor send is derived before and independently of the channel slider or gain control.
Preamp (Preamplifier)
An amplifier whose primary function is boosting or amplifying the output of a low-level audio-frequency source, such as a microphone, so that the signal may be further processed without appreciable degradation of the signal-to-noise ratio.
Preamp Out
A means of obtaining an output signal from the preamplifier of a channel of a mixer or musical instrument amplifier. The preamp output is generally a line-level signal.
Proximity Effect
An increase in low-frequency response when a unidirectional microphone is used close to a sound source.
R
Reactance
A resistive-like property that offers opposition to electron flow in an alternating current (AC) circuit. There are two types of reactance: capacitive reactance (XC) and inductive reactance (XL). Reactance varies with frequency.
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.
Reflection
The bouncing back or return of sound waves from walls or other obstacles that 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 the output of a loudspeaker in a sound reinforcement system gets back into a microphone or sound system input at a sufficient level and resonant frequency, the system can go into regeneration or feedback oscillation.
Resistance
Opposition to the flow of electrical current. Measured in ohms.
Resistor
An electronic component designed to have a definite amount of resistance. It is used in circuits to limit current flow or provide a voltage drop.
Resonance
A tendency of mechanical parts, loudspeaker cones, enclosure panels, or electrical circuits to vibrate at or emphasize one particular frequency when that frequency or one near it occurs.
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.
Return
An input 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 reflection from physical boundaries. Digital reverb uses electronic processing to introduce multiple delay paths that simulate natural reverberation.
Reverberation
The sustaining of acoustical energy in a room after the direct sound from the source ceases. Reverberation is caused by reflections and scattering of sound energy from the boundary surfaces of the room.
RIAA
Stands for Recording Industry Association of America. RIAA equalization is used for vinyl records, and an RIAA phono preamp is required when using a magnetic phono cartridge.
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 Value)
The square root of the time average of the square of a quantity. For a periodic quantity, the average is taken over one complete cycle. RMS voltage is 0.707 times the peak voltage of a sine wave.
Roll Off
A signal is rolled off when it is attenuated or reduced in level above or below a certain frequency. The amount of roll off is rated in decibels per octave.
RT60 (Reverberation Time)
The time required for sound to drop 60 dB in level once the source of sound has been stopped. The -60 dB measurement is taken below the steady-state level after initial transients or fluctuations have settled.
S
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
The minimum input signal required to produce a specified level of output. In an amplifier, input sensitivity is the amount of voltage at the input necessary to drive the amplifier to its rated power output. Loudspeaker sensitivity is usually rated as the SPL produced at a given distance from the loudspeaker with a specified amount of power.
Series
An arrangement of circuit components, end-to-end, to form a single path for current.
Series-Parallel
A circuit in which some components or elements are connected in parallel, and one or more of these parallel combinations are in series with other components of the circuit.
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, for example, boosts or cuts frequencies above the selected point.
Shift
A control found on some musical instrument amplifiers that shifts the center frequency of the mid-range control.
Signal-to-Noise Ratio (S/N)
The ratio of the amplitude or level of a desired signal at any point to the amplitude or level of noise at the same point.
Sine Wave
A wave whose amplitude varies as the mathematical sine of a linear function of time. Also known as a sinusoidal wave.
Single Source
A single speaker or cluster of speakers arranged into an array that produces sound as if it originated from a single or point source.
Slapback Echo
An echo caused by reflections off the rear wall in many auditoriums. Severe slapback echo can be distracting for musicians onstage and can make following the beat difficult.
Slew Limiting
The failure of an amplifier's output to move as fast, in terms of voltage, as the input would require it to move.
Slew Rate
Refers to the ability of an amplifier's output to accurately reflect the input waveform's rise-time transients. An amplifier may be rated with a slew rate of a certain number of volts per microsecond.
Snake
A multiconductor shielded input cable used when necessary to locate a mixer a long distance from the stage and microphones.
Sound
A pressure-wave motion propagated in an elastic medium such as air, producing an auditory sensation in the ear through changes in pressure. Sound waves are produced by a vibrating body in contact with air.
Sound Level Meter
An instrument used to measure noise and sound pressure levels, or SPL, calibrated in decibels.
Sound Fields
Direct Field
The sound that emanates directly from a sound source or loudspeaker.
Indirect Field
Sound perceived from behind a speaker system when no direct field is present.
Near Direct Field
The sound field generated close to the source or loudspeaker. It is generally considered the sound field within a distance from the source of less than two wavelengths.
Far Direct Field
The sound field perceived at a distance from the source loudspeaker that is greater than two wavelengths.
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 ceilings.
Reverberant Field
That sound field beyond critical distance where most of the energy arriving at the listener is in the form of reflected energy from the room's boundaries.
Spectrum
Refers to a particular band of frequencies. The normal acoustic sound spectrum is the range of human auditory perception, approximately 20 Hz to 20,000 Hz. Subsonic frequencies are below the audible range, while ultrasonic frequencies are above it.
Spectrum Analyzer
See Real Time Analyzer (RTA).
SPL (Sound Pressure Level)
The level or intensity at a point in a sound field. SPL measures deviations above and below normal atmospheric pressure and is expressed in decibels.
Splitter
A box into which one microphone or signal is connected and from which two or more individual outputs are available for that signal. It is often used when a separate monitor mix is required.
Standing Wave
Standing waves occur in rooms because of boundaries. A standing wave is a sound wave that, once excited, remains in a fixed pattern, with positive air-pressure peaks and negative air-pressure troughs remaining in the same positions within the room's boundaries.
Stereo
In a sound reproduction system, stereo refers to the use of two separate signal-processing channels driving two separate power amplifiers, which in turn power two separate speaker systems. In sound reinforcement, a stereo mixer may also be used to drive a mono system.
Sub-Master
A separate mixing bus assigned to a group of instruments or vocals 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.
Switching Jack
An input or output 1/4-inch phone jack that performs a switching function in addition to providing an input or output for a signal.
T
THD (Total Harmonic Distortion)
When a single frequency of a specified level is applied to the input of a system, THD is the distortion caused by nonlinearities in the system and is expressed as a percentage of harmonic content relative to the fundamental signal.
Timbre
Timbre refers to the musical quality or character of sound. It is related to the fundamental frequency and the level and number of associated harmonics. Different instruments playing the same note at the same loudness can sound different because of their different harmonic content.
Transducer (X-DCR)
Any device or element that converts an input signal into an output signal of a different form. A transducer changes energy from one form to another. A microphone changes acoustical energy into electrical energy, while a loudspeaker changes electrical energy into mechanical and acoustical energy.
Transformer (X-FMR)
An electrical component consisting of multiturn coils of wire placed in a common magnetic field that transfers electrical energy from one circuit to another. A transformer passes alternating current (AC) and does not pass direct current (DC).
Transformer Balanced (X-FMR BAL)
An input or output coupled by means of a transformer in a configuration that makes it balanced. A transformer-balanced input or output can provide common-mode rejection, reducing interference signals that are common to both conductors.
Transient
Rapidly changing peaks of short duration in the level of musical instruments, such as a cymbal crash or a rim shot on a snare drum. A transient has a very short or no sustain time.
Transient Distortion
Transient distortion interferes with the ability of an amplifier to accurately follow abrupt changes in volume, such as the sudden burst of sound when an instrument is first played. Minimum transient distortion is important for clean and crisp sound.
Transient Response
The ability of an amplifier or loudspeaker to accurately follow abrupt changes, such as the sudden burst of sound generated by an instrument. Good transient response is important for clear and crisp overall sound.
Triamp
Separating the audio spectrum into three bands, 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.
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 provide the common-mode rejection of a balanced system.
Unbalanced Input
An input in which one of the two terminals is at ground potential or connected to chassis ground.
V
Velocity
In audio, the velocity or speed of sound is approximately 1,130 feet per second. The speed of sound changes slightly with temperature, humidity, and altitude.
Voltage
Voltage is a measurement of electrical pressure or the potential to do work. Voltage is sometimes called EMF, or electromotive force. The familiar 120 volts at a wall socket is an example of available electrical pressure.
Volts (Voltage)
Potential difference or electromotive force (EMF).
Volume
The intensity or loudness of sound.
SPL VU (Volume Unit)
A unit for expressing the audio-frequency power level of a complex electronic waveform such as speech or music. Zero VU is referenced to 1 milliwatt of power.
VU Meter
A meter that indicates the audio-frequency power level or volume units of a complex electronic waveform.
W
Watt
A unit of measure of power. The electrical wattage of an amplifier describes the power it can develop to drive a speaker. Amplifier wattage requirements depend greatly upon the speakers being used, the size of the listening room, and the average loudness being played through the speakers.
Wavelength
In audio, the wavelength of sound is the actual physical distance that one complete cycle of sound energy occupies in air for a given frequency. The wavelength is found by dividing the velocity of sound by the frequency. A sound wave with a frequency of 1,000 Hz has a wavelength of approximately 1.13 feet when the speed of sound is 1,130 feet per second.
Woofer
A low-frequency speaker specialized in bass or low-frequency reproduction.
X
XLR
A connector, sometimes called a Cannon connector, used for interfacing audio components. The connector commonly used on low-impedance microphones is an XLR connector.
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