Electronics

acoustic radiometer An instrument for measuring the intensity of a sound wave (see SOUND IN- TENSITY) in terms of the unidirectional steady- state pressure exerted at a boundary as a result of absorption or reflection of the wave.
acoustic reactance Unit, ACOUSTIC OHM. The imaginary-number component of ACOUSTIC IMPEDANCE. It can take the form of ACOUSTIC CAPACITANCE or ACOUSTIC INDUCTANCE.
acoustic reflectivity The ratio Fr/Fi, where Fr is the rate of flow of sound energy reflected from a surface and Fi is the rate of flow of sound energy incident to the surface.
acoustic refraction The deflection of sound waves being transferred obliquely between media that transmit sound at different speeds.
acoustic regeneration See ACOUSTIC FEEDBACK. acoustic resistance Unit, ACOUSTIC OHM. The real-number component of ACOUSTIC IMPEDANCE. The opposing force that causes acoustic energy to be dissipated in the form of heat. It is attributed to molecular friction in the medium through which sound passes. See ACOUSTIC
OHM.
acoustic resonance In an enclosed chamber with
walls that reflect sound waves, resonance that occurs at certain wavelengths because the echoes
combine in and out of phase. Speaker enclosures
almost always have resonance at certain frequencies. This effect can be used to an advantage when
it is necessary to get good bass (low-frequency)
response from a relatively small speaker.
acoustic resonator
1. A chamber, such as a box,
cylinder, or pipe, in which an air column resonates
at a particular frequency.
2. A piezoelectric, magnetostrictive, or electrostrictive body that vibrates at a resonant audio frequency that is governed by
the mechanical dimensions of the body when an
audio voltage at that frequency is applied.
acoustics
1. The physics of sound. The study and applications of acoustic phenomena.
2. The qualities of an enclosure or sound chamber (room, auditorium, or box) that describe how sound waves behave in it.
acoustic scattering The spreading of a sound wave in many directions as a result of diffraction, reflection, or refraction.
acoustic suspension A loudspeaker design that allows exceptional low-frequency reproduction for a fairly small physical size. An airtight enclo- sure is used to increase the tension on the speaker cone.
acoustic system
1. A coordinated array of acous- tic components (e.g., acoustic filters, resonators, etc.) that responds to sound energy in a predetermined manner.
2. An audio-frequency system in which sound energy is converted into electrical energy, processed, and then reconverted into sound energy for a clearly defined purpose.
acoustic telegraph A telegraph that gives audible signals, as opposed to visual signals or printed messages.
acoustic transducer
1. Any device, such as head- phones or a loudspeaker, for converting audio- frequency electrical signals into sound waves.
2. Any device, such as a microphone, for converting sound waves into alternating, pulsating, or fluctuating currents.
acoustic transmission The direct transmission of sound energy without the intermediary of electric currents.
acoustic transmission system A set of components designed to generate acoustic waves.
acoustic transmissivity Also called acoustic transmitivity. The ratio et/ei, where et is the sound energy transmitted by a medium, and ei is the incident sound energy reaching the surface of the medium. Acoustic transmissivity is proportional to the angle of incidence.
acoustic treatment Application of sound-absorb- ing materials to the interior of an enclosure or room to control reverberation.
acoustic wave The traveling vibration, consisting of molecular motion, via which sound is trans- mitted through a gas, liquid or solid. Usually refers to sound waves in air.
acoustic wave filter See ACOUSTIC FILTER.
acoustoelectric effect The generation of a voltage
across the faces of a crystal by sound waves traveling longitudinally through the crystal.
acoustoelectronics A branch of electronics concerned with the interaction of sound energy and
electrical energy in devices, such as surface-wave
filters and amplifiers. In such devices, electrically
induced acoustic waves travel along the surface
of a piezoelectric chip and generate electrical en-
ergy. Also called praetersonics and microwave
acoustics.
ac plate current Symbol, IP(ac). The ac component of plate current in a vacuum tube.
ac plate resistance Symbol, RP(ac). The dynamic plate resistance of an electron tube. RP(ac) equals dEP/dIP, where EP is the plate voltage and IP is the plate current, for a constant value for grid volt- age EG.

acoustic depth finder A direct-reading device for determining the depth of a body of water, or for locating underwater objects via sonic or ultra- sonic waves transmitted downward and reflected back to the instrument.
acoustic dispersion Variation of the velocity of sound waves, depending on their frequency.
acoustic elasticity
1. In a loudspeaker enclosure, the compressibility of air behind the vibrating cone of the speaker.
2. In general, the compressibility of any medium through which sound passes.
acoustic electric transducer A transducer, such as a microphone or hydrophone, that converts sound energy into electrical energy. Compare ELECTRICAL/ACOUSTIC TRANSDUCER. Also see ACOUSTIC TRANSDUCER.
acoustic feedback A usually undesirable effect that occurs when sound waves from a loud- speaker (or other reproducer) reach a microphone (or other input transducer) in the same system. This can cause an amplifier to oscillate, with a resultant 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 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 re-
production 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 con- sists 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 sub audible 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.

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acoustic Pertaining to audible sound distur-
bances, usually in air (versus audio-frequency
currents or voltages).
acoustic absorption The assimilation of energy
from sound waves passing through or reflected by
a given medium.
acoustic absorption loss That portion of sound
energy lost (as by dissipation in the form of heat)
because of ACOUSTIC ABSORPTION.
acoustic absorptivity The ratio of sound energy
absorbed by a material to sound energy striking
the surface of the material.
acoustic attenuation constant The real-number
component of the complex acoustical propagation
constant, expressed in nepers per unit distance.
acoustic burglar alarm An alarm that receives the
noise made by an intruder. The alarm device responds to the impulses from concealed microphones.
acoustic capacitance The acoustic equivalent of
electrical capacitance.
acoustic clarifier In a loudspeaker system, a set of cones attached to the baffle that vibrate to absorb
and suppress sound energy during loud bursts.
acoustic communication Communications by
means of sound waves. This can be through the
atmosphere, or it can be through solids or liquids, such as a taut wire, a body of water, or the earth.
acoustic compliance COMPLIANCE in acoustic
transducers, especially loudspeakers. It is equivalent to electrical capacitive reactance.
acoustic consonance An effect that occurs when two objects are near each other but not in physical
contact, and both have identical or harmonically
related resonant frequencies. An example is shown
by two tuning forks with identical fundamental frequencies. If one fork is struck and then brought near the other, the second fork will begin vibrating. If the second fork has a fundamental frequency that is a harmonic of the frequency of the first fork, the second fork will vibrate at its own resonant frequency. See HARMONIC, RESONANCE.
acoustic coupling Data transfer via a sound link between a telephone and a pickup/reproducer. Was once common in computer terminals and facsimile machines. This scheme has been largely replaced by hard wiring and optical coupling.
acoustic damping The deadening or reduction of the vibration of a body to eliminate (or cause to die out quickly) sound waves arising from it.
acoustic delay line Any equivalent of a special transmission line that introduces a useful time delay between input and output signals. In one form, it consists of a crystal block or bar with an input transducer at one end and an output transducer at the other. An electrical input signal in the first transducer sets up sound waves that travel through the interior of the crystal; the piezoelectric reaction of the crystal to sound vibrations sets up an output voltage in the second transducer. The delay is caused by the time required for the acoustic energy to travel the length of the crystal bar.