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acoustic feedback • acoustic radiator 9
This can cause an amplifier to oscillate, with a resultant
rumbling, howling, or whistling.
acoustic filter Any sound-absorbing or transmitting
arrangement, or combination of the two, that
transmits sound waves of desired frequency while
attenuating or eliminating others.
acoustic frequency response The soundfrequency
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
loudspeakers operated from a suitable oscillator,
buzzer, bell, or flame) and mechanical devices
(tuning forks, bells, string, or whistles).
acoustic grating A set of bars or slits that are parallel
to one another and arranged a fixed distance
apart so that an interference pattern forms as
sound passes through. Used to determine the
wavelength of acoustic waves.
acoustic homing system 1. A system that uses a
sound signal for guidance purposes. 2. A guidance
method in which a missile homes in on
noise generated by a target.
acoustic horn A tapered tube (round or rectangular,
but generally funnel-shaped) that directs
sound and, to some extent, amplifies it. So called
to distinguish it from a microwave horn.
acoustic howl See ACOUSTIC FEEDBACK.
acoustician 1. A person skilled in acoustics (an
acoustics technician). 2. An AUDIOLOGIST.
acoustic impedance Unit, ACOUSTIC OHM. The
acoustic equivalent of electrical impedance. Like
the latter, acoustic impedance is the total opposition
encountered by acoustic force. Also like electrical
impedance, acoustic impedance has
resistive and reactive components: ACOUSTIC
RESISTANCE and ACOUSTIC REACTANCE.
acoustic inductance Also called inertance. The
acoustic equivalent of electrical inductance.
acoustic inertance See ACOUSTIC INDUCTANCE.
acoustic inhibition See AUDITORY INHIBITION.
acoustic intensity See SOUND INTENSITY.
acoustic interferometer An instrument that evaluates
the frequency and velocity of sound waves
in a liquid or gas, in terms of a standing wave set
up by a transducer and reflector as the frequency
or transducer-to-reflector distance varies.
acoustic labyrinth A loudspeaker enclosure
whose internal partitions form a maze-like path
or “tube” lined with sound-absorbing material.
The tube effectively runs from the back of the
speaker down to where it terminates in a MOUTH
or PORT that opens at the front of the enclosure.
The labyrinth provides an extremely efficient reproduction
system because of its excellent acoustic
impedance-matching capability.
acoustic lens A system of barriers that refracts
sound waves the way that an optical lens does
with light waves.
acoustic line Baffles or other such structures
within a speaker that act as the mechanical equivalent
of an electrical transmission line to enhance
the reproduction of very low bass frequencies.
acoustic load A device that serves simultaneously
as the output load of an amplifier and as a transducer
of electrical energy into acoustic energy
(e.g., headphones or a loudspeaker).
acoustic memory In a computer, a volatile memory
element employing an acoustic delay line, often
incorporating quartz or mercury as the
transmission and delay element.
acoustic mirage A type of sound distortion in
which the listener experiences the illusion of two
sound sources when there is only one. The phenomenon
is caused by the effect of a large temperature
gradient in the air or water through
which the sound passes.
acoustic mode Crystal-lattice vibration without
producing an oscillating dipole.
acoustic noise Interferential (usually disagreeable)
sounds carried by the air (or other propagation
medium) to the ear or to an acoustic transducer.
This is in contrast to electrical noise, which consists
of extraneous current or voltage impulses
and is inaudible until converted into sound.
acoustic ohm The unit of acoustic resistance, reactance,
or impedance. One acoustic ohm equals
the volume velocity of 1 cm/s produced by a
sound pressure of 1 microbar (0.1 Pa). Also called
acoustical ohm.
acoustic phase constant The imaginary-number
component of the complex acoustic propagation
constant expressed in radians per second or radians
per unit distance.
acoustic phase inverter A bass reflex loudspeaker
enclosure.
acoustic pressure 1. The acoustic equivalent of
electromotive force, expressed in dynes per
square centimeter; also called acoustical pressure.
2. Sound pressure level.
acoustic propagation The transmission of sound
waves, or subaudible or ultrasonic waves, as a
disturbance in a medium, rather than as an electric
current or electromagnetic field.
acoustic radiator A device that emits sound
waves. Examples are the cone of a loudspeaker,
the diaphragm of a headphone, and the vibrating
reed of a buzzer.