Page 171 - The Master Handbook Of Acoustics

146 CHAPTER SEVEN

Acoustically Coupled Spaces

The shape of the reverberation decay can
Sound pressure level, dB B the decay is due to acoustically coupled
point to acoustical problems in the space.
One common effect that alters the shape of

spaces. This is quite common in large pub-
lic gathering spaces, but is also found in
offices, homes, and other small spaces. The
principle involved is illustrated in Fig. 7-
11. The main space, perhaps an audito-
A
rium, is acoustically quite dead and has a
Time
reverberation time corresponding to the
FIGURE 7-11 slope A. An adjoining hall with very hard

Reverberatory decay with a double slope due to surfaces and a reverberation time corre-
acoustically coupled spaces. The shorter reverberation sponding to slope B opens into the main
time represented by slope A is that of the main room. room. A person seated in the main hall near
A second, highly reflective space is coupled through the hall opening could very well experi-
an open doorway. Those seated near the doorway are
subjected first to the main-room response and then ence a double-slope reverberation decay.
to the decay of the coupled space. Not until the sound level in the main room
falls to a fairly low level would the main
room reverberation be dominated by sound fed into it from the slowly
decaying sound in the hall. Assuming slope A is correct for the main
room, persons subjected to slope B would hear inferior sound.

Electroacoustically Coupled Spaces

What is the overall reverberant effect when sound picked up from a
studio having one reverberation time is reproduced in a listening room
having a different reverberation time? Does the listening room rever-
beration affect what is heard? The answer is definitely yes. This prob-
4
lem has been analyzed mathematically by Mankovsky. In brief, the
sound in the listening room is affected by the reverberation of both stu-
dio and listening room as follows:

The combined reverberation time is greater than either alone.

The combined reverberation time is nearer the longer reverbera-
tion time of the two rooms.