Defining Reverberation - October 5th, 2008
In any enclosed space, there is a finite length of time required for any steady-state sound field, developed by a sound source, to die once the sound source is turned off. The sound heard during the length of time it takes for the initial sound to die out, is called reverberation. The reverberation time is the length of time in seconds that reverberation can be heard. The time it takes for a 60 db decay is called RT60.
Spaces that qualify as large rooms can effectively use the myriad of equations based on the original assumptions of Sabine for reverberation. In a small space like a dedicated home cinema, using RT60, mean free path and other Sabine statistical equations, is invalid. It is fundamentally incorrect to apply the Sabine equations to a small room, like a home cinema.
In a home cinema installation, we use acoustic absorptive panels to control a specific energy return, rather than as absorbers to change a statistical sound field level. A frequent error in a home cinema design , is the random distribution of absorptive materials, in the mistaken belief that a reverberant sound field is present. Using effective measurement tools leads to specific placement of such materials, only in the finite areas where it can actually control a specific energy return. For a quick overview of reverberation in a small-room, read ”Home Cinema Reverberation Times “.