Page 25 - The Illustrated Dictionary of Electronics

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10 acoustic radiometer • ac plate resistance

acoustic radiometer An instrument for measuring acoustic scattering The spreading of a sound
the intensity of a sound wave (see SOUND IN- wave in many directions as a result of diffraction,
TENSITY) in terms of the unidirectional steady- reflection, or refraction.
state pressure exerted at a boundary as a result acoustic suspension A loudspeaker design that
of absorption or reflection of the wave. allows exceptional low-frequency reproduction
acoustic reactance Unit, ACOUSTIC OHM. The for a fairly small physical size. An airtight enclo-
imaginary-number component of ACOUSTIC sure is used to increase the tension on the
IMPEDANCE. It can take the form of ACOUSTIC speaker cone.
CAPACITANCE or ACOUSTIC INDUCTANCE. acoustic system 1. A coordinated array of acous-
acoustic reflectivity The ratio F r/F i, where F r is tic components (e.g., acoustic filters, resonators,
the rate of flow of sound energy reflected from a etc.) that responds to sound energy in a predeter-
surface and F i is the rate of flow of sound energy mined manner. 2. An audio-frequency system in
incident to the surface. which sound energy is converted into electrical
acoustic refraction The deflection of sound waves energy, processed, and then reconverted into
being transferred obliquely between media that sound energy for a clearly defined purpose.
transmit sound at different speeds. acoustic telegraph A telegraph that gives audible
acoustic regeneration See ACOUSTIC FEEDBACK. signals, as opposed to visual signals or printed
acoustic resistance Unit, ACOUSTIC OHM. The messages.
real-number component of ACOUSTIC IMPE- acoustic transducer 1. Any device, such as head-
DANCE. The opposing force that causes acoustic phones or a loudspeaker, for converting audio-
energy to be dissipated in the form of heat. It is frequency electrical signals into sound waves. 2.
attributed to molecular friction in the medium Any device, such as a microphone, for converting
through which sound passes. See ACOUSTIC sound waves into alternating, pulsating, or fluc-
OHM. tuating currents.
acoustic resonance In an enclosed chamber with acoustic transmission The direct transmission of
walls that reflect sound waves, resonance that oc- sound energy without the intermediary of electric
curs at certain wavelengths because the echoes currents.
combine in and out of phase. Speaker enclosures acoustic transmission system A set of compo-
almost always have resonance at certain frequen- nents designed to generate acoustic waves.
cies. This effect can be used to an advantage when acoustic transmissivity Also called acoustic
it is necessary to get good bass (low-frequency) transmitivity. The ratio e t/e i, where e t is the
response from a relatively small speaker. sound energy transmitted by a medium, and e i is
acoustic resonator 1. A chamber, such as a box, the incident sound energy reaching the surface of
cylinder, or pipe, in which an air column resonates the medium. Acoustic transmissivity is propor-
at a particular frequency. 2. A piezoelectric, mag- tional to the angle of incidence.
netostrictive, or electrostrictive body that vibrates acoustic treatment Application of sound-absorb-
at a resonant audio frequency that is governed by ing materials to the interior of an enclosure or
the mechanical dimensions of the body when an room to control reverberation.
audio voltage at that frequency is applied. 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 trav-
eling longitudinally through the crystal.
acoustoelectronics A branch of electronics con-
cerned 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, I P(ac). The ac component
of plate current in a vacuum tube.
acoustics 1. The physics of sound. The study and ac plate resistance Symbol, R P(ac) . The dynamic
applications of acoustic phenomena. 2. The qual- plate resistance of an electron tube. R P(ac) equals
ities of an enclosure or sound chamber (room, dE P /dI P , where E P is the plate voltage and I P is the
auditorium, or box) that describe how sound plate current, for a constant value for grid volt-
waves behave in it. age E G .