Factors influencing effectiveness of Sound Absorbing foams.
by Duncan Geddes
Airflow, cell size and density, are the main factors influencing the effectiveness of sound absorption in acoustic foams(aka sound deadening foams). Increasing the cell count (ie the number of cells per 25mm of length) of the foam improves the sound absorption at all frequencies. The acoustic absorptivity a specifies the ratio of un-reflected sound in a series of audio frequencies to an incident sound energy. From measurement of acoustic absoptivity, problems of sound absorption in the low and middle frequency ranges can be adequately solved with the use of flexible polyurethane foams.
Lower foam densities permit greater penetration of the sound waves into the foam, and minimise sound reflectance. Sound absorption efficiency also improves with increasing foam thickness and surface area. By using pyramid, wedge, eggbox and waffle structures, the surface area can be increased which effectively helps acoustic absorptivity.
Acoustic foam reduces or eliminates background noises by controlling the reverberation (echo) that sound can make by bouncing off walls.