The tendency of a space to maintain sound energy is quantified by its "reverberation". One could describe reverberation as a smooth, slowly decaying echo.

A sonic event occurring within a space possesses energy, and this energy will remain until some force acts upon it and converts it to another form of energy. Air particles serve to reduce sound energy, albeit at a very low rate. A sound occurring within a space will maintain its energy for more time if there exists very little sound absorbing material, and it will maintain its energy for less time if there exists a significant amount of evenly distributed sound absorbing material. Larger spaces normally possess more (longer) reverberation, which means that a sound occurring in that space will remain audible for a relatively long period of time (2-5 seconds). Small, highly absorptive spaces, such as anechoic chambers, will possess virtually no reverberation (<0.25 seconds). An extreme demonstration of the principle exists in the "reverb chamber," which is a small space with smooth marble walls, floor, and ceiling, and can possess reverberation times upward of 5-10 seconds.