Porous materials absorb sound because their large surface area creates frictional losses.
Evidence
Another form of energy loss occurs when the sound wave hits or travels through some porous material. In this case there is a very large surface area of interaction in the material due to all the fibers and holes. There are frictional losses at the surface of any material due to the interaction of the velocity component of the sound wave with the surface. A larger surface area will have a higher loss, which is why porous materials such as cloth or rock wool absorb sound waves strongly. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 344
Categorization
- XREF: Connects to the reader’s existing interest in sound absorption for quieting spaces, relevant to their noise/silence reading thread about one square inch of silence and soundscapes. — connects to: Friction acts like rent proportional to the energy an oscillator stores; Maximum sound output requires balancing radiation loss against internal friction; Walls absorb sound by converting organized acoustic energy into heat through friction (+5 more)
- corroborated: 4 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 344