P. Cobo
Sound can be absorbed by several mechanisms, the most important being the conversion of acoustic energy in heat by viscous-thermal dissipation. Although this dissipation is produced even in the air, it is quantitatively much more important inside some specially designed materials, named acoustic materials. These materials are usually placed lining walls (surface absorbers), or in full contact with the noise field (volume absorbers).
The fundamentals of sound absorption can be learnt in the following book:
https://editorial.csic.es/publicaciones/libros/12465/978-84-00-09952-7/…
