Acoustic Properties of Curtains and Carpets - August 27th, 2008
Curtains and carpets are typical porous absorbers. In a porous absorber, sound propagates within the pores of the material, so viscous and thermal effects take place. Acoustic energy then gets dissipated.
In order to improve the curtains efficiency, one must place the curtain in a place where the particle velocity is high. The particle velocity next to a home cinema’s boundary (wall) is relatively small. That would mean that a curtain with deeper folds would offer greater absorption, due to the fact of the greater distance from the wall. Also the extra material will increase the resistance, so we will have a higher dissipation of the acoustic energy.
It is worth mentioning that a fabric of higher density will increase efficiency.
We usually see all dedicated home cinema rooms having carpet covering the whole floor area. The carpet is sitting next to the room’s boundary (floor), so it will only have an effect on the high frequencies. The absorption would vary depending on the type of carpet used, and also on the type of underlay fitted. An open celled underlay would result in increase of thickness of the absorbing material. That would increase the absorption generated.
It is obvious that in order to absorb low frequencies, due to the large wavelengths, one would need to place the porous absorber quite far from the wall, where the particle velocity is high. That would require really thick absorbers, or to be spaced really far off the wall. The use of a resonant absorber would be ideal, but we will cover that topic in another article.