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Sound Energy that is transmitted by pressure waves in air or other materials and is the objective cause of the sensation of hearing. Commonly called noise if it is unwanted. Sound, physical phenomenon that stimulates the sense of hearing. In human beings, hearing takes place whenever vibrations of frequencies between about 15 and 20,000 hertz reach the inner ear. The hertz (Hz) is a unit of frequency equalling one cycle per second. Such vibrations reach the inner ear when they are transmitted through air, and the term sound is sometimes restricted to such airborne vibrational waves. Modern physicists, however, usually extend the term to include similar vibrations in liquid or solid media. Sounds of frequencies higher than about 20,000 hertz are called ultrasonic.
See also: Acoustics, Attenuation of Sound in Air, A Weighting, Cavity Acoustics, Direct Sound, Ear, Hearing, Macrosonics, Noise, Reciprocity, Sonar, Sound Level Meter, Sound Pressure Level, Sound Waves, Speed of Sound, Subsonic, Supersonic, Ultrasonic.
  
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