JBL CINEMA SOUND SET UP - Subwoofers

F. Subwoofers
Subwoofers are an integral part of cinema loudspeaker systems installed in mid- and large-size
houses. In specifying them, the designer must take into account the reduced sensitivity of the ear to
low frequency sounds. Figure 21 shows the Robinson-Dadson equal loudness contours. Note that, for
a reference level of 85 dB at 1 kHz, frequencies in the range of 30 to 40 Hz will have to be reproduced
15 to 20 dB louder in order to be perceived at the same subjective level.
‘L
.-.
FREQUENCY W Hz
Figure 21.
Robinson-Dadson equal loudness contours.
Since low frequencies are essentially nondirectional, we commonly specify subwoofer
U.
hardware by calculating the acoustical power requirements in the cinema for a given sound pressure
level. Assuming that the reverberation times in modern cinemas follow the data presented in Figures
11 and 12, we can present the data shown in the following table:
-P-@Jt
m3
270m3
10
(10,ooo w.ft.)
540m3
15
(20,ooo cu.ft.)
1350m3
20
(50,ooocu.tt.)
2700 m3
40
(1ocl.oooal.ft.)
5400m3
100
(2oo.ooocu.ft.)
Table 2: Acouetical Power vereue Cinema Volume
3 Derived from the revertwant level requirements, based on average reverberation times in houses with the
tabulated volumes.