If a sound wave hits a wall a part of the energy will be refl ected, another part will be absorbed in the wall and a third fraction will be transmitted. According to the sketch the sound absorption and the sound transmission can be defi ned as following:
Sound absorption coefficient:
Sound transmission factor:
Due to the very small values for the sound transmission factor, the sound transmission is usually described with the sound reduction index R (also called transmission loss TR) expressed in dB.
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