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
at 1
frequencies in the range of 30 to 40 Hz will have to be reproduced
15 to 20
louder in order to be perceived at the same subjective level.
FREQUENCY
Figure 21. Robinson-Dadson equal loudness contours.
Since low frequencies are essentially nondirectional, we commonly specify subwoofer
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:
10
15
40
100
Table 2:
Power
Cinema Volume
Derived from the
level requirements, based on average
times in houses with the
tabulated volumes.
