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.
Sound absorption value
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.
Absorption and absorption area
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
Basic data, e.g. the sound absorption value, is based on data from the Danish Building Research Institute’s indoor climate manual, the company DELTA and the acoustic consultant Jan Voetmann. The results in this report are meant to be indicative only and Troldtekt A/S cannot be held liable for any losses or damage which may result from use of the calculator.