What materials are effective absorbers of sound?

Different materials will absorb certain frequencies of sound better than other frequencies, but some of the best absorbers of sound are soft objects. Materials such as felt, carpeting, drapes, foam, and cork are good at matching the impedance of a sound wave and reflecting back very little sound. Materials such as concrete, brick, ceramic tile, and metals, on the other hand, are effective reflecting materials of sound. That is why gymnasiums (with hardwood floors, concrete walls, and metal ceilings) have relatively long reverberation times, while concert halls furnished with upholstered seats, carpeted floors, and long drapes have relatively short reverberation times. People are also effective sound absorbers, so a full concert hall has different acoustic properties than an empty one.


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