Page 179 - The Master Handbook Of Acoustics

154 CHAPTER SEVEN

100%
Permissible bass rise in reverberation time 50%

0
63 125 250 500 1 kHz
Frequency - Hz

FIGURE 7-16
Permissible bass rise of reverberation time for voice studios derived by subjective eval-
11
uation in controlled tests by BBC researchers. (After Spring and Randall. )

Living Room Reverberation Time
The reverberation characteristic of the average living room is of inter-
est to the high-fidelity enthusiast, the broadcaster, and the recording
specialist. This living room is where the high-fidelity recordings are
to be played. Further, the quality control monitoring room of the
broadcast and recording studio must have a reverberation time not
too far from that of the living room in which the final product will be
heard. Generally, such rooms should be “deader” than the living
room, which will add its own reverberation to that of recording or
broadcast studio.
Figure 7-17 shows the average reverberation time of 50 British liv-
12
ing rooms measured by Jackson and Leventhall using octave bands of
noise. The average reverberation time decreases from 0.69 second at
125 Hz to 0.4 second at 8 kHz. This is considerably higher than earlier
measurements of 16 living rooms made by BBC engineers in which
reverberation times between 0.35 and 0.45 were found on the average.
Apparently, the living rooms measured by the BBC engineers were bet-
ter furnished than those measured by Jackson and Leventhall and, pre-
sumably, would agree better with living rooms in the United States.
The 50 living rooms of the Jackson-Leventhall study were of vary-
ing sizes, shapes, and degree of furnishing. The sizes varied from 880
to 2,680 cu ft, averaging 1550 cu ft. Figure 7-15 shows an optimum