Acoustics - Extended environments: reverb time

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In this case too, we'd use the RT60 factor we described earlier to measure the reverberation time. Due to the environment's dimension and the sound source having a higher volume (orchestras, amplified music bands), reverb tends to be very present. In particular, when sound reinforcement is lacking [Sound reinforcement ] , at a certain distance from the stage reverberated sound is almost the only sound source the spectator perceives. Seeing that each hall has its own characteristic reverb time, each of them will be more apt to certain music genres than another. A hall that has a very long reverb time isn't suitable for rock concerts, whereas it will be ideal to blend the harmonies of a symphonic orchestra. It's important to bear in mind that reverb time varies depending on whether the hall is empty or full of spectators who absorb part of the sound. This is an important thing to bear in mind during rehearsals, which usually take place in empty halls. The sound engineer must remember that the acoustics will inevitably be different when the actual performance takes place, and must therefore take necessary measures. If reverb is uniform all over the hall, we can say that it has a constant amplitude. The following diagram illustrates the intensity of two sounds (the direct sound coming from the source and the reverberated sound) as distance from the sound source (the stage) increases:

Environmental acoustics - Direct sound and reverberated sound in a hall

Direct sound and reverberated sound in a hall

As we can see the intensity of the reverb remains constant at any distance from the stage. The direct sound on the other hand attenuates as distance increases, and there is a point (R), defined as room radius (aka critical distance), at which the two sounds have the exact same intensity. Beyond the R point the reverberated sound overtakes the direct one.

The following table shows the reverberation times of some of the World's most famous halls:

Table 15.4. Reverberation Time of some of the World's halls 

Name of the hallYear of constructionVolume (m3)RT60(sec)
Royal Albert Hall (London)1871860002.6
Carnegie Hall (Amsterdam)1887187002.0
Symphony Hall (Boston)1900187401.8
Royal Festival Hall (London)1951220001.5
New Philharmonic (Berlin)1963260002.0


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