Reverberation

Reverberation (Fig. 50-3) is the persistence of sound after the source of the sound has ceased, as a result of repeated reflections. Reverberation affects the intelligibility of speech and the quality of music. The reverberation time of a space is the amount of time that sound bounces around a room before dying out to an inaudible level. It is defined as the time required for sound energy to decay 60 dB, or to one millionth of its initial intensity.

The sound in a room is a combination of direct sound from the source and reflected sound from walls and other obstructions. Our ears sense reverberation as a mixture of previous and more recent sounds. The reverberation time is longer in a room with a larger volume, as the distances between reflections are longer. When sound-absorbing materials are added to a space, the reverberation time decreases as sounds are absorbed.

The reverberation time of a room should be appropriate to the use of the space. For speech in offices and small rooms, a reverberation time of 0.3 to 0.6 second is desirable. The reverberation time for auditoriums ranges from 1.5 to 1.8 seconds. You can control the quality of the sound by modifying the amount of absorptive or reflective finishes in a space.

Figure 50-3 Reverberation.

ZTf The reverberation of sounds in lecture halls, theaters, houses of worship, and concert halls sustains and blends sounds, making them much smoother and richer than they would be in open air. Short reverberation times are best for speech, as they allow clarity for consonant sounds. However, some reverberation enriches a speaker's voice, and gives the speaker some sense of how well the voice is carrying to the audience.

Music benefits from longer reverberation times that extend and blend the sounds of instruments and voices. Music sounds dead and brittle with too short a reverberation time, but loses clarity and definition when the reverberation time is too long.

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