Page 226 - Master Handbook of Acoustics

FIGURE 11-12 An illustration of the effects of reverberation on the intelligibility of speech.
Understanding the word “back” depends on apprehending the later, lower-level consonant “… ck,”
which can be masked by reverberation if the reverberation time is too long.

Excessive reverberation can impair the intelligibility of speech by masking the lower level
consonants. In the word “back,” the word is unintelligible without clear audibility of the “ck” part.
Understanding the “ck” ending is the only way to distinguish “back” from bat, bad, bass, ban, or bath.
In this simplified way, we observe the effect of reverberation on the understandability of speech and

the reason why speech is more intelligible in rooms having lower reverberation times. Similarly, in a
highly reverberant room, a speaker may have to speak slowly to be understood. It is a straightforward
procedure to predict with reasonable accuracy the intelligibility of speech in a space, from
geometrical factors and knowledge of reverberation time.
On the other hand, a completely dead room, or an outdoor environment, is not optimal for speech

intelligibility; at even a moderate distance away, the sound level from a speaker may be too low to
clearly hear speech. The reverberation in live rooms add acoustical power to original sound sources,
reinforcing them and making them more audible, as well as more pleasant sounding. A dead room
adds less power to the source, and the overall sound is softer. A good room design must therefore
balance acoustical gain with intelligibility. In part, this means that different reverberation times
determine whether a room is best suited for speech or music.

Influence of Reverberation on Music

The effect of reverberation on speech can be easily gauged according to the intelligibility of speech.
The effect of hall resonance or reverberation on music is intuitively grasped but is more difficult to

quantify. For example, a reverberation time that seems suitable for one type of music may be