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Glossary – A

The signal fed to the left-hand loudspeaker of a stereo two-speaker system.
Direct comparison of sound quality between audio playback components, accomplished by frequently switching from one to another.
Abbreviation for automatic bass compensation; a circuit utilized in some audio equipment to increase the amplitude of the bass tones and make them sound more natural at low volume levels.
Limiting values of operating conditions, applicable to any device of specified type as defined in its published data.
Dissipation of the energy of a sound wave into other forms owing to its reaction with matter.
The fraction of sound power which is absorbed on reflection at any surface. (It ranges between O and 1, and unless otherwise stated, is for a frequency of 512 Hz at normal incidence.)
Abbreviation for alternating electrical current, which periodically reverses its direction, as opposed to DC (direct current).
Control of the upper frequencies in terms of total response heard by the audience in a cinema, to minimize the effect of unwanted random noise in the system.
Alternative term for lacquer disc.
A standard plastic base for magnetic recording tape.
Pertaining to sound or to the science of sound.
The energy lost by conversion into heat or other forms when sound passes through or is reflected by a medium.
The ratio of sound energy absorbed by a surface to the sound energy arriving at the surface. Equal to 1 minus the reflectivity of the surface.
The real part of the acoustic propagation constant; neper per section, or unit distance.
In a sound medium, a measure of volume displacement per dyne per square centimeter. The unit is centimeter to the fifth power per dyne.
In a loudspeaker, the point at which a sound wave appears to originate.
A system of cones loosely attached to the baffle of a speaker and designed to vibrate and absorb energy during sudden loud sounds, thereby suppressing them.
The measure of volume displacement of a sound medium when subjected to sound waves. Also, that type of acoustic reactance which corresponds to capacitive reactance in an electrical circuit.
A device that retards one or more signal vibrations by causing them to pass through a solid (or liquid).
The change in speed of sound with frequency.
The compressibility of the air in a speaker enclosure as the cone moves backwards. Also, the compressibility of any material through which sound is passed.
Specification of the significant acoustic properties of a listening area.
A device designed to transform sound energy into electrical energy, and vice versa.
Also called acoustic regeneration. The mechanical coupling of a portion of the sound waves from the output of an audio amplifying system to a preceding part or input circuit (such as a microphone) in the system. When excessive, acoustic feedback produces a howling sound in the speaker.
A sound-absorbing device that selectively suppresses certain audio frequencies while allowing others to pass.
The voltage-attenuation frequency characteristic measured into a resistive load, producing a bandwidth approaching sufficiently close to the maximum.
A transducer such as a speaker, which converts electrical or other forms of energy into sound.
Also called a horn. A tube of varying cross section having different terminal areas, which change the acoustic impedance to control the directivity of the sound pattern.
Total opposition of a medium to sound waves. Equal to the force per unit area on the surface of the medium, divided by the flux (volume velocity or linear velocity multiplied by area) through that surface. Expressed in ohms and equal to the mechanical impedance divided by the square of the surface area.
A type of acoustic reactance that corresponds to inductive reactance in an electrical circuit. (The resistance to movement or reactance offered by the sound medium because of the inertia of the effective mass of the medium.) Measured in acoustic ohms.
The limit approached by the quotient of acoustic power being transmitted at a given time through a given area divided by the area as the area approaches zero.
A special speaker enclosure having partitions and passages to prevent cavity resonance and to reinforce bass response.
An array of obstacles that refracts sound waves in the same way that an optical lens refracts light waves. The dimensions of these obstacles are small compared to the wavelengths of the sound being focused. Also, a device that produces convergence or divergence of moving sound waves. When used with a speaker enclosure, an acoustic lens widens the beam of the higher-frequency sound waves.
Mechanical equivalent of an electrical transmission line. Baffles, labyrinths, or resonators are placed at the rear of a speaker enclosure to assist in reproduction of very low audio frequencies.
A mode of crystal-lattice vibration that does not produce an oscillating dipole.
The unit of acoustic resistance, reactance, or impedance. One acoustic ohm is present when a sound pressure of 1 dyne per cm2 produces a volume velocity of 1 cm3 per s.
The imaginary part of the acoustic propagation constant. The commonly used unit is the radian per second or unit distance.
In non electrical phonographs, the method of producing a recording by linking the needle directly to a flexible diaphragm.
In an electroacoustic transducer, the part that initiates the radiation of sound vibration. A speaker cone or an earphone diaphragm are examples.
That part of the acoustic impedance due to the effective mass of the medium, that is, to the inertia and elasticity of the medium through which the sound travels. The imaginary component of acoustic impedance, expressed in acoustic ohms.
The ratio of the rate of flow of sound energy reflected from the surface on the side of incidence to the incident rate of flow.
A bending of sound waves when passing obliquely from one medium to another in which the velocity of sound is different.
That component of the acoustic impedance which is responsible for the dissipation of energy due to friction between molecules of the air or other medium through which sound travels. Measured in acoustic ohms; analogous to electrical resistance.
An increase in sound intensity as reflected waves and direct waves combine in phase. May also be due to the natural vibration of air columns or solid bodies at a particular audio frequency.
An enclosure that intensifies those audio frequencies at which the enclosed air is set into natural vibration.
The irregular reflection, refraction, or diffraction of a sound wave in many directions.
A plane or curved sheet of sound absorbent or sound reflective material used for modification of an acoustic environment.
A sealed loudspeaker cabinet, in which the enclosed volume of air acts as an acoustic resistance to the speaker cone.
Arrangement of components in devices designed to reproduce audio frequencies in a specified manner.
An assembly of elements adapted to the transmission of sound.
Use of certain sound-absorbing materials to control the amount of reverberation in a room, hall, or other enclosed space.
A traveling vibration by which sound is transmitted in air or other medium. The characteristics of these waves may be described in terms of change of pressure, or particle displacement, or of density.
A device designed to separate sound waves of different frequencies. (Through electroacoustic transducers, such a filter may be associated with electric circuits.)
Science of production, transmission, reception, and effects of sound. Also, in a room or other locations, those characteristics that control reflections of sound waves, and thus the sound reception in the room.
A network or circuit capable of supplying a power or voltage gain, as for example, an amplifier.
Analog to digital converter. Circuit whose output is a digital representation of an analog input.
Duplication of a voice or instrument track with a delay of a few milliseconds to increase the impact or simulate the effect of more performers.
Abbreviation for Audio Engineering Society.
Abbreviation for audio frequency, a range that extends from 10 Hz to 20 kHz.
Abbreviation for automatic frequency control, a circuit commonly used in FM receivers to compensate for frequency drift to keep the tuner "locked" to a selected station.
The noise reduction unit in an optical sound recorder.
The air space within a horn or an acoustic chamber.
1. The process of positioning tape heads and amplifier presets for optimum tape performance. 2. The adjustment of a device to bring it into conformance with published specifications.
A continually fluctuating electric flow, at one instant positive, the next negative.
Amplitude modulation; a method of superimposing information on an RF carrier by amplitude variation of the carrier.
Acoustic environment. The combination of reverberation and background noise which characterizes the sound in a given hall or studio.
Acoustic noise in a room or other location. Usually measured with a sound-level meter.
The difference between the L and R signals.
Magnification or enlargement.
An electronic device that magnifies or enlarges audio voltage or power signals.
Also called peak value: the maximum value of a waveform (with respect to one polarity).
Nonlinear relation of input and output induced harmonics. A function of voltage fluctuations or power consumption.
Electronic signal whose waveform resembles that of the original. The signal is not converted to digital form.
A low-reflection audio-frequency enclosure.
A room in which reflected sound energy is negligible; used for measurement of speaker and microphone characteristics.
Wire or system of wires (also bars, plates, dishes) supported at a height above the ground for the purpose of radiating or of collecting electromagnetic waves.
The percentage of speech units understood by a listener.
Proportion of height to width.
Microphone placed at some distance from the performers to pick up the general ambience.
1. Related to rise time. The period of time during which a tone increases to full amplitude after a musical instrument starts to emit a tone. 2. Time taken for a limiter or compressor to produce the necessary gain change.
Opposite of amplification; reduction of audio voltage or power.
An undesired variation of gain or sensitivity with frequency.
A resistive network inserted in a microphone or other line to lower the level by a specified number of decibels.
Wave motion in air with a frequency between 20 and 20,000 Hz that produces a sensation of audibility. The audible spectrum varies slightly from individual to individual. High frequency perception decreases with age of the listener.
Pertaining to frequencies corresponding to a normally audible sound wave. These frequencies range approximately from 15 Hz to 20 kHz.
An instrument that measures audio-frequency power with reference to a predetermined level. Usually calibrated in decibels.
A specialized type of audio amplifier that eliminates much of the background noise from recordings, and provides volume expansion.
Spurious demodulation of interfering radio-frequency voltages in an audio system.
One who enjoys experimenting with high-fidelity equipment and who is likely to seek the best possible reproduction.
An oscilloscope built into a stereo or stereo-quad system for monitoring signal amplitude and separation.
Tape machine facility giving fast location of chosen points on the tape.
A trade name of the MCI Company, to describe their tape transport control system.
A transformer designed with a single, tapped winding that serves as both primary and secondary.
Perpendicular line through center of diaphragm.
The angle between the gap in a tape head and the longitudinal axis of the tape (should be 90 degrees).
The mechanical adjustment of the record or playback head to bring it into proper alignment (90 degrees) with the tape path.

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