Absorption materials are used to control sound within a space. Acoustically absorptive materials are typically rated with an NRC number. Some materials may also be rated with a CAC number (usually ceiling tiles) and yet others may be rated in Sabines.

Absorption panels can be used to control harsh reflections, reduce reverberation time, or eliminate echo. Absorption panels can also be used to reduce the propagation of sound in otherwise open areas (i.e., down a long hallway).

TREATING THE REVERBERANT SPACE

Controlling a reverberant sound field with sound absorbing materials is often the most practical method of noise control for institutional, industrial, exposition and correctional facilities. Experiments in psycho acoustics and speech intelligibility have shown that long reverberation times make the understanding of speech difficult or impossible. Also as the reverberation time is shortened, the background noise level is reduced as speech intelligibility improves. Improvement in communications has long been recognized as an important feature for most public, commercial and industrial spaces. A good acoustical environment in school classrooms and child care centers is now also recognized as a critical factor in the development of early language skills in very young children.

In many cases, the use of sound absorbing panels optimized for sound absorption in the speech frequencies, can provide a satisfactory reverberation time (T60 = 0.4 seconds for example) while preserving the necessary signal to noise ratio without the need for amplification.

Acoustic absorption panels come in many shapes, sizes, and materials. Below are some examples: