The Illustrated Dictionary of Electronics - Loscha

8 ac meter • acoustic feedbackac meter A meter that is intended to work only onalternating current or voltage. Such meters includeiron-vane and rectifier types.ac noise 1. Electromagnetic interference originatingin the ac power lines. 2. Electrical noise of arapidly alternating or pulsating nature.ac noise immunity In computer practice, the abilityof a logic circuit to maintain its state, despiteexcitation by ac noise.acous Abbreviation for ACOUSTIC.acoustic Pertaining to audible sound disturbances,usually in air (versus audio-frequencycurrents or voltages).acoustic absorption The assimilation of energyfrom sound waves passing through or reflected bya given medium.acoustic absorption loss That portion of soundenergy lost (as by dissipation in the form of heat)because of ACOUSTIC ABSORPTION.acoustic absorptivity The ratio of sound energyabsorbed by a material to sound energy strikingthe surface of the material.acoustic attenuation constant The real-numbercomponent of the complex acoustical propagationconstant, expressed in nepers per unit distance.acoustic burglar alarm An alarm that receives thenoise made by an intruder. The alarm device respondsto the impulses from concealed microphones.acoustic capacitance The acoustic equivalent ofelectrical capacitance.acoustic clarifier In a loudspeaker system, a set ofcones attached to the baffle that vibrate to absorband suppress sound energy during loud bursts.acoustic communication Communications bymeans of sound waves. This can be through theatmosphere, or it can be through solids or liquids,such as a taut wire, a body of water, or theearth.acoustic compliance COMPLIANCE in acoustictransducers, especially loudspeakers. It is equivalentto electrical capacitive reactance.acoustic consonance An effect that occurs whentwo objects are near each other but not in physicalcontact, and both have identical or harmonicallyrelated resonant frequencies. An example is shownby two tuning forks with identical fundamental fre-quencies. If one fork is struck and then broughtnear the other, the second fork will begin vibrating.If the second fork has a fundamental frequencythat is a harmonic of the frequency of the first fork,the second fork will vibrate at its own resonantfrequency. See HARMONIC, RESONANCE.acoustic coupling Data transfer via a sound linkbetween a telephone and a pickup/reproducer.Was once common in computer terminals andfacsimile machines. This scheme has been largelyreplaced by hard wiring and optical coupling.acoustic damping The deadening or reduction ofthe vibration of a body to eliminate (or cause todie out quickly) sound waves arising from it.acoustic delay line Any equivalent of a specialtransmission line that introduces a useful timedelay between input and output signals. In oneform, it consists of a crystal block or bar with aninput transducer at one end and an output transducerat the other. An electrical input signal inthe first transducer sets up sound waves thattravel through the interior of the crystal; thepiezoelectric reaction of the crystal to sound vibrationssets up an output voltage in the secondtransducer. The delay is caused by the time requiredfor the acoustic energy to travel the lengthof the crystal bar.acoustic depth finder A direct-reading device fordetermining the depth of a body of water, or forlocating underwater objects via sonic or ultrasonicwaves transmitted downward and reflectedback to the instrument.acoustic dispersion Variation of the velocity ofsound waves, depending on their frequency.acoustic elasticity 1. In a loudspeaker enclosure,the compressibility of air behind the vibratingcone of the speaker. 2. In general, the compressibilityof any medium through which soundpasses.acoustic electric transducer A transducer, suchas a microphone or hydrophone, that convertssound energy into electrical energy. CompareELECTRICAL/ACOUSTIC TRANSDUCER. Alsosee ACOUSTIC TRANSDUCER.acoustic feedback A usually undesirable effectthat occurs when sound waves from a loudspeaker(or other reproducer) reach a microphone(or other input transducer) in the same system.