Page 24 - The Illustrated Dictionary of Electronics

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acoustic feedback • acoustic radiator 9

This can cause an amplifier to oscillate, with a re-
sultant rumbling, howling, or whistling.
acoustic filter Any sound-absorbing or transmit-
ting arrangement, or combination of the two, that
transmits sound waves of desired frequency while
attenuating or eliminating others.
acoustic frequency response The sound-
frequency range as a function of sound intensity.
A means of describing the performance of an
acoustic device.
acoustic generator A device that produces sound
waves of a desired frequency and/or intensity.
Examples are electrical devices (headphones or acoustic line Baffles or other such structures
loudspeakers operated from a suitable oscillator, within a speaker that act as the mechanical equiv-
buzzer, bell, or flame) and mechanical devices alent of an electrical transmission line to enhance
(tuning forks, bells, string, or whistles). the reproduction of very low bass frequencies.
acoustic grating A set of bars or slits that are par- acoustic load A device that serves simultaneously
allel to one another and arranged a fixed distance as the output load of an amplifier and as a trans-
apart so that an interference pattern forms as ducer of electrical energy into acoustic energy
sound passes through. Used to determine the (e.g., headphones or a loudspeaker).
wavelength of acoustic waves. acoustic memory In a computer, a volatile mem-
acoustic homing system 1. A system that uses a ory element employing an acoustic delay line, of-
sound signal for guidance purposes. 2. A guid- ten incorporating quartz or mercury as the
ance method in which a missile homes in on transmission and delay element.
noise generated by a target. acoustic mirage A type of sound distortion in
acoustic horn A tapered tube (round or rectangu- which the listener experiences the illusion of two
lar, but generally funnel-shaped) that directs sound sources when there is only one. The phe-
sound and, to some extent, amplifies it. So called nomenon is caused by the effect of a large tem-
to distinguish it from a microwave horn. perature gradient in the air or water through
acoustic howl See ACOUSTIC FEEDBACK. which the sound passes.
acoustician 1. A person skilled in acoustics (an acoustic mode Crystal-lattice vibration without
acoustics technician). 2. An AUDIOLOGIST. producing an oscillating dipole.
acoustic impedance Unit, ACOUSTIC OHM. The acoustic noise Interferential (usually disagreeable)
acoustic equivalent of electrical impedance. Like sounds carried by the air (or other propagation
the latter, acoustic impedance is the total opposi- medium) to the ear or to an acoustic transducer.
tion encountered by acoustic force. Also like elec- This is in contrast to electrical noise, which con-
trical impedance, acoustic impedance has sists of extraneous current or voltage impulses
resistive and reactive components: ACOUSTIC and is inaudible until converted into sound.
RESISTANCE and ACOUSTIC REACTANCE. acoustic ohm The unit of acoustic resistance, re-
acoustic inductance Also called inertance. The actance, or impedance. One acoustic ohm equals
acoustic equivalent of electrical inductance. the volume velocity of 1 cm/s produced by a
acoustic inertance See ACOUSTIC INDUCTANCE. sound pressure of 1 microbar (0.1 Pa). Also called
acoustic inhibition See AUDITORY INHIBITION. acoustical ohm.
acoustic intensity See SOUND INTENSITY. acoustic phase constant The imaginary-number
acoustic interferometer An instrument that eval- component of the complex acoustic propagation
uates the frequency and velocity of sound waves constant expressed in radians per second or radi-
in a liquid or gas, in terms of a standing wave set ans per unit distance.
up by a transducer and reflector as the frequency acoustic phase inverter A bass reflex loudspeaker
or transducer-to-reflector distance varies. enclosure.
acoustic labyrinth A loudspeaker enclosure acoustic pressure 1. The acoustic equivalent of
whose internal partitions form a maze-like path electromotive force, expressed in dynes per
or “tube” lined with sound-absorbing material. square centimeter; also called acoustical pres-
The tube effectively runs from the back of the sure. 2. Sound pressure level.
speaker down to where it terminates in a MOUTH acoustic propagation The transmission of sound
or PORT that opens at the front of the enclosure. waves, or subaudible or ultrasonic waves, as a
The labyrinth provides an extremely efficient re- disturbance in a medium, rather than as an elec-
production system because of its excellent acous- tric current or electromagnetic field.
tic impedance-matching capability. acoustic radiator A device that emits sound
acoustic lens A system of barriers that refracts waves. Examples are the cone of a loudspeaker,
sound waves the way that an optical lens does the diaphragm of a headphone, and the vibrating
with light waves. reed of a buzzer.