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Sound absorption (absorption)

When a source of sound is initiated in a closed space, that energy does not build up in an instant. The finite velocity of propogation of the sound wave is responsible for the nature of the energy released. Each 'pencil' of sound sent out by a source is relfected many times from the walls. Each time a portion of the energy is absorbed by the walls until it dissipates completely. The energy in the direct sound is greater than the reflected sound because of the smaller distance and the absence of absorption by the walls which occurs in the reflected sound. (paraphrased from Music, Physics, and Engineering, by Harry Olson, pp. 267-68.)