4. ReverberationAcoustics of enclosures have as the main factor reverberation time (RT). Reverberation is the continuation of sound in an enclosed space after the sound source has stopped. Quantitatively it is the am for a sound to drop by 60 dB. It is axiomatic therefore, that it has a direct relationship to the type of material covering of the surface of the hall, and its volume. Too high a RT causes undue echo effects, which cause distortion due to the direct sound from the speaker and the reflected sound from the wall surfaces having a time delay. This can be a source of speech confusion and is a factor for poor speech intelligibility.
On the other hand if the reverberation time is too low it is more difficult it is to sustain sound energy over the distance of a large enclosed area. Reverberation tune planning should account for the type of activity required. Music or singing requires a different RT from speech to be effective in the hall of ITTHO which has a volume of 10 000 m3 the optimum RT is 0.9 seconds for speech. However, the same room used for musical concerts would require a higher value of RT.
Reverberation time can be controlled by the application of absorbent materials. However, care both in the selection of the absorption coefficient of the materials and where they are placed in the hall is vital. Placing the material at the back of the hall for example would have the effect of killing the direct speech to the back of the audience. On the other hand placing the material on sidewalls can mitigate the effect of time delay between the direct sound of the speaker and the delayed reflected sound from the walls.
