SOUND SHADOW

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A phenomenon caused by the ABSORPTION or obstruction of a SOUND WAVE by an object in its path. The effect produced is perceived as a reduction in LOUDNESS depending on the observer's position with respect to the sound source and obstructing object and is greatest when the three are aligned.

Compare: CANCELLATION, INTERFERENCE, SOUND INSULATION.

High frequencies are more easily absorbed than lower ones, and are less susceptible to DIFFRACTION, that is, they move less easily around objects because of their short WAVELENGTHs. Therefore, the ATTENUATION of high frequencies is noted in a sound shadow. As well, more reflected sound from the environment is likely to be received than direct sound. See: SOUND PROPAGATION, section 2.

Since the head will absorb high frequencies more easily than low ones, it will create a sound shadow for the ear farthest away from the sound source, and therefore the phenomenon plays a role in sound localization. The effect, however, seems less important than time differences for BINAURAL HEARING except in the upper frequency region (see PINNA). Blind people use the sound shadow effect for orientation, as well as reflected sound and other cues. See: ECHOLOCATION.

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