pneumatic loudspeaker[nu̇′mad·ik ′lau̇d‚spēk·ər]
an acoustic radiator in which the sound is generated by modulation of a flow of compressed air. Pneumatic loudspeakers were used in the 1930’s and 1940’s to transmit orders and information in large harbors, river ports, and other areas with a high noise level.
A pneumatic loudspeaker consists of a compressor and a tank to produce a stream of compressed air, a modulator to vary the stream according to audio-frequency oscillations supplied to it, and a horn to radiate the sound. Such loudspeakers produced an acoustic power of up to 2 kilowatts and reproduced audio-frequency oscillations with frequencies of up to 2.5–3.5 kilohertz, with high internal noise and substantial nonlinear distortion.
REFERENCESOlson, H. F., and F. Massa. Prikladnaia akustika. Moscow, 1938. (Translated from English.)
Beranek, L. Akusticheskie izmereniia. Moscow, 1952. (Translated from English.)