Glossary of Audio Terminology
A
AC (Alternating Current): Electrical current that alternates direction (positive to negative). AC is often contrasted with direct current (DC), commonly produced by batteries.
Absorption: The tendency of sound waves to be soaked up by soft surfaces. Opposite: reflection.
Acoustic Feedback: Feedback, the dreaded “sound man’s (and sound woman’s) curse,” is caused by a regeneration of sound leaving a speaker and entering a microphone. This tone – a sustained shriek – is a self-perpetuating cycle which can be stopped by decreasing the volume.
Acoustics: 1. The science or scientific study of sound. 2. The properties of a room or environment that affect the qualities of sound.
Acoustic Power Output: The output, as measured in watts, of anything that generates sound.
Acoustic Suspension: A type of speaker cabinet which is sealed to control the action of its woofer and prevent the leakage of air.
Ambient Noise Level: “Background” noise – from any source – that affects the listener’s ability to hear what is produced by a sound system.
Amperes, Amperage (Amps): Units of electrical current.
Amplifier (Amp): 1. An electronic device that increases the amplitude of a signal. 2. A combination speaker/amplifier designed for use with an instrument, as with a guitar amp or keyboard amp. See preamp; power amplifier.
Amplitude: 1. The strength of sound waves or an electrical signal, as measured against a mean. 2. That which determines loudness.
Anechoic: 1. The complete absence of reflected sound (echo). 2. An environment that prevents (through dissipation or absorption of sound waves) all reflected sound, as in an anechoic chamber.
Attenuate: To make weaker. An attenuator uses resistance to reduce output voltage, as with a volume control.
B
Balanced Line: A pair of ungrounded conductors whose voltages are opposite in polarity but equal in magnitude. Balanced lines reduce interference from external sources like radio frequencies and light dimmers.
Basket: The frame to which a driver’s cone is mounted
Bass: The lower end of the frequency range, from about 20 Hz to about 300 Hz.
Bass Reflex: A speaker that, as a means of enhancing the efficiency of the reproduction of bass frequencies, channels some of the sound pressure generated by its woofer(s) through an opening (port) in its cabinet.
Biamplification: The use of separate amplifiers to power woofers and tweeters. See: Crossover- Electronic, Crossover- Passive.
Board: Also control board. See: Mixer, Mixing Console.
C
CPS (Cycles Per Second): The number of plus/minus voltage swings or compressions/rarefactions of air molecules occurring each second in an electrical or audio signal; usually expressed as hertz (Hz).
Cardioid: “Heart” shaped pattern exhibited by some microphones which reduces pick-up from the sides and back.
Clipping: Audible distortion that occurs when a signal’s level exceeds the limits of a particular circuit. When an amp is “turned up too loud,” and begins to distort, it is said to be clipping. On an oscilloscope clipping appears to flatten the tops and/or bottoms of the waveforms.
Compression Driver: A driver, designed for use with a horn, which utilizes a diaphragm (rather that a cone to reproduce mid and high frequencies.
Compressor: A device that reduces – compresses – a signal’s dynamic range.
Condenser Microphone: A mic that depends on an external power supply or battery to electrostatically charge its condenser plates.
Conductor: A substance – in electronics, usually a metal – that allows the free flow of electrons.
Cone: The vibrating diaphragm, employed in some speaker designs, that generates sound waves.
Console: A large or elaborate mixer.
Critical Distance: The distance from a sound source at which sound pressure levels emitted by the source equal those being reflected off of other sources.
Crossover (Crossover Network), Electronic: An electronic device or circuit that, when inserted between a mixer and amplifier, divides the audio spectrum into individual frequency ranges (low, high, and/or mid) before sending them to specialized amplifier/speaker combinations. An advantage of this type of crossover is that it increases efficiency.
Crossover (Crossover Network), Passive: An electronic device that, when inserted after the amplifier, divides the audio spectrum into individual frequency ranges (low, high, and/or mid) before sending them to specialized speakers. See: Tweeter, Woofer.
Current: The movement – or flow – of electrons.
D
dB (Decibel): 1. A relative unit of measure between two sound or audio signal levels. A difference of 1 dB is considered to be the smallest that can be detected by the human ear. An increase of 6 dB equals twice the sound pressure. 2. As a measure of sound pressure levels, used to indicate loudness. Note – dB is NOT “cool soundman lingo” for a direct box! See: DI.
DC (Direct Current): Electrical current that flows in only one direction.
Delay: 1. The postponement of an audio signal for a specific time, usually measured in milliseconds. 2. A device designed to delay an audio signal.
DI: The proper abbreviation for a direct box. Anyone who says “Hey, you! Toss me that DB!” just sounds plain silly! Every good soundman knows that dB stands for decibel! See: dB (Decibel).
Diaphragm: 1. The radiating surface of a compression driver; its vibrations emit sound waves. 2. The moving element of a microphone.
Directivity: The ability of a speaker or horn to direct sound to a given area which can be described by its directivity factor (Q).
Dispersion: The area throughout which the sound produced by a speaker is distributed.
Distortion: Any discrepancy between the source material and the sonic output of a sound system.
Dynamic Microphone: A microphone that converts sound into electrical pulses by means of a moving electromagnetic coil.
Dynamic Range: The difference between the softest and loudest extremes within an audio signal.
Dynamics Processing: The use of electronic devices to control the levels of audio signals and compress or expand their dynamic range.
E
Effects Loop: Inputs and outputs that allow the sending of an audio signal to and from a signal processor such as a reverb unit, delay, gate, or limiter.
Efficiency: The ratio of a device’s energy output to its energy intake.
Equalization (EQ): The electronic manipulation of specific frequencies.
Equalizer (EQ): A device that permits the precise control of specific frequency ranges.
Expander: An electronic device that increases dynamic range by reducing a signal’s level any time it falls below a specific threshold.
F
Feedback: See: Acoustic Feedback.
FerroFluid: An emulsion containing metal particles, used to conduct heat away from a speaker’s voice coil.
Filter: A device that removes unwanted frequencies or noise from a signal.
Flat: The state of an audio signal or tone whose frequency is unaltered by equalization. On most mixers and equalizers flat is indicated by the tone controls being at dead center.
Fletcher Munson Curve: A graphic representation of average hearing responses at particular sound pressure levels.
Frequency: 1. The number of sound waves that pass a given point in one second. 2. The determiner of pitch.
Frequency Response: The range of frequencies that are reproducible by a speaker or electronic component.
Front of House (FOH): The components of a PA that are directed toward the audience, as opposed to the back-of-house or monitor system.
G
Gain: 1. The amplification characteristic of an electrical or mechanical device. 2. The amount of volume that may be achieved before acoustical feedback occurs.
Gate: An electronic device that increases dynamic range by cutting off a signal when its level falls below a specific threshold.
H
Hz (Hertz): A unit of measure that equals one cycle per second.
High Pass Filter: A circuit that discriminates between high and low frequencies and allows only the high frequencies to pass.
Horn: An acoustical transformer which, when coupled to a driver, provides directivity and increases the driver’s loudness.
Hypercardioid: A narrower heart-shaped pick-up pattern than that of cardioid microphones.
I
Impedance: The measure of the total resistance to the current flow in an alternating current circuit, expressed in ohms, as a characteristic of electrical devices (particularly speakers and microphones). Most speakers are rated at 8 ohms. Microphones are usually classified as being either high impedance (10,000 ohms or greater) or low impedance (50 ohms to 250 ohms).
Inductance: A circuit’s opposition to a change in current flow.
Input Overload Distortion: Distortion caused by too great an input signal being directed to an amplifier or preamplifier. Input overload distortion is not affected by volume control settings and most frequently occurs when mics are positioned too close to the sound source. Input overload distortion is controllable through the use of an attenuator.
Inverse Square Law: The law that states that in the absence of reflective surfaces, sound pressure (or light) falls off at a rate inverse to the square of the distance from its source. In other words, every time you double your distance from the sound source, the sound pressure level is reduced by 6 dB.
J
Jack: A female input or output connector, usually for a mic or an instrument.
L
Limiter: A device that electronically controls or “limits” the peak levels of program material.
Line Level: A signal whose voltage is between approximately 0.310 volts and 10 volts across a load of 600 ohms or greater.
Load: Any device to which power is delivered.
Low Pass Filter: A circuit that discriminates between high and low frequencies and allows only the low frequencies to pass.
M
Microphone Processor: A device that, when installed between a mic and an amp or preamp, allows the manipulation of the signal originating at the mic.
Mixer: An electronic device that permits the combining of a number of inputs into one or more outputs. Mixers commonly provide a variety of controls – tone, volume, balance and effects – for each “channel.” See: Board, Console.
Monitor: A speaker or earphone dedicated to making it possible for a performer to hear – or monitor – his/her own performance.
Motor: The magnet structure of a speaker.
N
Noise Gate: A device that attenuates a signal when the program level falls below a preset threshold.
O
Ohm: The basic unit of the measurement of resistance.
OHM’s Law: The law that states the relationship between current, resistance and voltage in an electrical circuit: Amperage times resistance equals applied voltage (V=IR).
Omnidirectional: Capable of picking-up sound or radiating sound equally from all directions.
Oscilloscope: An electronic device that displays, on a video screen, a representation of an electrical signal.
Over-Equalization: Adjustment of the tone controls on an equalizer to or beyond the point at which sound quality is adversely affected.
P
PA: Abbreviation of public address system: one or more speakers connected to an amplifier; may include a mixer and any combination of sound reinforcement devices.
Pad: An attenuator.
Patch Cord: A short electrical cable used to connect individual components of a sound system.
Personal Monitor: A monitor that is small enough to be directed at a specific performer.
PFL: Pre Fade Level or Pre Fade Listen – this little button on a mixing console allows you to hear only that channel in the headphones when it is pressed. It is also referred to as a “Solo” button to “solo up” a channel. It does not mean “press this button when your lead guitar has a solo!” In live sound reinforcement, PFL (pronounced “piffle” <g>) each channel individually to set channel gain to at or about -0- on the meter. PFL is also useful in identifying your off-key singers so you can turn them down in the house! 
Piezo Tweeter: A driver which is dedicated to the reproduction of high frequencies and operated by means of a crystal rather than an electromagnet.
Phantom Power: Operating voltage supplied to a condenser mic by a mixer or external power source.
Phase: The relationship of an audio signal or sound wave to a specific time reference.
Phase Shift: The phase relationship of two signals at a given time, or the phase change of a signal over an interval of time.
Pitch Tone: a function of frequency.
Polarity: A condition which has two states (in or out) and is usually described in one of three ways: 1. Acoustical to electrical (microphone): Positive pressure at diaphragm produces positive voltage at pin 2 of XLR or at the tip of a ¼-inch phone plug. 2. Electrical to acoustic: Positive voltage into the “plus” terminal of a speaker causes the speaker’s diaphragm to move forward (produces positive pressure). 3. Electrical to electrical: Positive voltage into pin 2 of an XLR plug produces positive voltage at the output (pin 2 of an XLR jack, the tip of a ¼-inch phone jack, or the red (plus) connector of a binding post (banana terminal).
Potentiometer (Pot): A variable resistor (rotary or linear) used to control volume, tone, or other functions of an electronic device.
Power Amplifier: An electronic device that increases the volume of a signal. A basic unit of all sound systems. Power amps are typically connected to a preamp which provides controls for individual functions: level, tone, etc.
Preamplifier: See: Power Amplifier.
Proximity Effect: An increase in the bass response of some mics as the distance between the mic and its sound source is decreased.
Q
Q: 1. A ratio obtained by complex mathematical calculations involving the relationship of a speaker’s direct radiated energy to its total radiated energy (directivity index). When measured on-axis, Q (which is dependent on frequency) is used to determine a speaker’s suitability for a particular application. 2. A very cool bad guy in “Star Trek – Next Generation!”
R
Radio Frequency Interference (RFI): Radio signals from external sources that invade and can be heard through, sound systems.
Reflection: A term that describes the amount of sound “bouncing” off of hard surfaces.
Rejection: A microphone’s ability to selectively exclude sounds coming from outside its pickup pattern.
Resistance: Opposition, measured in ohms, to the flow of electrical current.
Reverberation: Sound waves that continue to bounce around a space after the sound source has ended.
Room: Any enclosed space in which a performance is staged.
S
SPL (Sound Pressure Level): A measurement of the volume of sound, expressed in decibels (dB): a function of amplitude.
Sensitivity: The sound pressure level directly in front of the speaker (on axis) at a given distance and produced by a given amount of power.
Shield: A metal enclosure that prevents electronic components from being affected by unwanted interference. Shielded speakers may be placed near a TV, for instance, because their magnets cannot affect the picture tube.
Shelving: The setting of the on-axis output of complementary drivers (woofers, mid-range, tweeters) to provide the desired frequency response.
Signal: An electrical impulse.
Signal-to-Noise-Ratio: The ratio, expressed in dB, of an electronic device’s nominal output to its noise floor.
Snake: A cable – often running between the stage and control board – that combines multiple lines; used to connect mics, instruments and monitors to a mixer.
Sound Level Meter: A device that measures, in dB, the amplitude of sound waves.
Sound Pressure Level (SPL): The measurement of the loudness, or amplitude, of sound, expressed in dB.
Sound Reinforcement: The use of electronic devices to reinforce, alter or increase the level of sound.
Squawker: A common nickname for a mid-range driver.
T
Toe-in: The degree to which the inside front edges of a pair of speakers are angled toward each other.
Transducer: A device which converts sound into electrical energy (a microphone), or electrical energy into sound (a speaker).
Transformer: A device that alters electrical current.
Tweeter: A speaker (driver) that reproduces only frequencies above a certain range, usually about 3 kHz.
U
Unbalanced Line: Cable that consists of one conductor and a shield.
Unidirectional: A mic that picks-up sound primarily from one direction.
V
VCA (Voltage Controlled Amplifier): An amplifier whose output is controlled by varying its voltage rather than by direct resistance (as with a potentiometer).
Voice Coil: Wire, usually copper, wrapped around a former (tubular core). When attached to a cone or diaphragm, surrounded by a magnetic field, and set into vibration by an alternating current, a voice coil causes a speaker to emit sound waves.
Voltage: The electrical pressure (electromotive force) of a current within a circuit.
W
Watt: 1. A unit of measurement that equals about 1/746 horsepower or enough electrical energy to perform 1 joule per second. A joule describes the energy of 1 newton displaced 1 meter in the direction of the applied force. A newton is the amount of force needed to accelerate 1 kilogram 1 meter per second. 2. One volt multiplied by one amp.
Wedge: A monitor speaker, in the shape of a wedge, designed to sit on the floor and be directed toward the performer(s).
Woofer: A speaker (driver) that reproduces only frequencies below a certain range, usually about 800 Hz.
X
XLR Connector: A three pin connector widely used in the audio industry.
