Reverberation time (T)

Reverberation time (T) is the time in which the sound energy in a room has dropped to the millionth part of its original value, i.e. the sound pressure level has dropped by 60 dB. In simple terms, it indicates the time it takes for a sound event to become inaudible. In technical terms, the time taken for the sound pressure level in the room to fall by 60 decibels was defined as the reverberation time T.

The surface materials of a room, its walls, ceilings, floor etc. have a significant influence on its reverberation properties. The so-called reverberation of a room has a positive or negative influence on an activity carried out there. Smooth, sound-reflecting surfaces create a very reverberant working environment and are not suitable for concentrated work. The selection and arrangement of surface materials must therefore be adapted to the intended activity. Acoustic wall panels or acoustic partitions in offices are often used to reduce the reverberation time.

In this respect, the reverberation time is an important parameter for the acoustic assessment of a room. The reverberation time is a measure of the energy reduction in a room. The more sound absorption there is in a room, the faster sound energy is reduced and the shorter the reverberation time. People feel most comfortable when the reverberation time is between 0.2 and 0.5 seconds. In cooperation with architects and specialist planners, we have developed tools for calculating the reverberation time and for acoustic room design.

The reverberation time can be calculated using the Sabine’s formula for reverberation time. The discovery of the fundamental relationship between the volume of a room, the sound absorption of the surfaces present in the room and the reverberation time goes back to the experimental research work of the American physicist Wallace Clement Sabine (1868-1919). In 1898, Sabine found out that the reverberation time T is proportional to the volume of the room V and inversely proportional to the equivalent absorption area A.