acoustic radiator[ə′küs·tik ′rād·ē‚ād·ər]
a device for the excitation of sound waves in an elastic medium. An acoustic radiator can be built by using various sound-producing means: vibrations of solids and surfaces in an elastic medium (a string with a sounding board, a plate, a membrane, and so on); vibrations in the air itself (whistles, sirens, organ pipes, or the human vocal apparatus); periodic variations of temperature in the medium (thermophone and ionophone); and so forth.
The most important characteristics of an acoustic radiator are the frequency radiation range, the radiating power, and the directivity (the distribution of the radiated energy in space). Depending on the application of an acoustic radiator, the requirements for these characteristics will be different. A loudspeaker, for instance, should radiate sound in a wide range of frequencies from 30 Hz to 16 kHz and uniformly in all directions; but the acoustic radiator of an ultrasonic flaw detector should produce a narrow directional beam of ultrasonic waves with a single frequency of several MHz. To obtain an acoustic radiator with the required characteristics, computations of its sound field are carried out. However, accurate solutions can be attained only for radiators of the simplest shapes (a pulsating sphere, a vibrating sphere, and so forth) under conditions of small vibration amplitudes of the radiating surface; the great variety of acoustic radiators are reduced to these simple radiator types or combinations thereof.