| Reverberation time Reverberation time is defined as the time it takes for the sound pressure level to drop by 60 dB.  A short reverberation time gives the best possibilities for a clear and distinct sound picture, good speech intelligibility and minimising annoying background noise. Long reverberation times, which are typical in rooms with many hard surfaces, lead to poor speech intelligibility and echos and often contribute to a poor indoor environment. Typical reverberation times range from 0.3 seconds e.g. in cinemas with modern surround sound systems to approximately 7 seconds in large cathedrals. Just like sound absorption, reverberation time is frequency dependent. Therefore, it is important to state the required reverberation time at the relevant frequencies. For more information regarding recommended reverberation times for a variety of applications, go to the Requirements and legislation section. |
| Reverberation time estimates Most rooms with normal sound absorption can be estimated according to Sabines formula: T=0.16 x V / A where:
Equivalent absorption area (A) The equivalent absorption area is an expression for the total sound absorption of the room. It is calculated by multiplying the area of all sound absorbing surfaces by their absorption coefficient. A=a1S1 + a2S2 + ..............anSn Where a1, a2 ............. an=Sound absorption coefficients of the different surfaces in the room S1, S2 .............. Sn=The respective surface areas (m2) of the different surfaces. The total surface area S=S1+S2 + ............. Sn Sabines formula should only be used for rooms with a mean absorption coefficient am of max. 0.35. If this value is exceeded, the Sabine-Eyring formula shown below should be used: T=0.16 x V / ( S x In ( 1 / 1- am)) where In x ( 1 / ( 1 - am ) ) is determined from a standard curve when the mean absorption coefficient am is known. am=A / S |
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