Reverberation time is the time, measured in seconds, that passes between a sound source stopping and the sound dying out. In a church, the reverberation time is long, i.e. it takes the sound a long time to die out. On the other hand, in small rooms with a lot of furniture, curtains and carpets, the reverberation time is short. More accurately, the term reverberation time denotes the number of seconds it takes the sound level to drop 60 dB after the sound source has ceased.

The efficiency of a sound absorbing material is expressed by means of its sound absorption value. The sound absorption value is expressed using the Greek letter α (alpha) and alpha values are measured over a wide frequency range (bass, mid-range and treble). The sound absorption value not only depends on the material but also on how the material is installed.

The sound absorbing effect of an acoustic material depends partly on how effective the material is in itself and partly on how many square metres of the material you install. The effect is called the absorption and is simply the product of the sound absorption value and the actual number of square metres of material. If you install 100 square metres of an acoustic product with a sound absorption value of 0.6, the absorption will be 100 x 0.6, i.e. 60. The greater the absorption, the lower the reverberation time in the room.

Acoustic calculations from Troldtekt A/S are based on Sabine’s formula. According to this formula, the reverberation time (in seconds) for a room is directly proportional to the room’s volume (in m3 ) divided by the total absorption in the room (in m2 Sabine, ‘metric sabin’).