JBL CINEMA SOUND SET UP, Руководство пользователя

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frequencies tends to lower the reverberation time. Figure 11 shows the normal range of reverberation
time, as a function of the value at 500 Hz, while Figure 12 shows the acceptable range of
reverberation at 500 Hz as a function of room volume.
Variation of tion time
with frequency
0.1
12. Suggested of
The requirements of specifying the right finishing materials, along with any special needs for
added low-frequency absorption, fall squarely in the hands of the acoustical designer. In smaller
houses, there is often
choice but to make the space acoustically ‘dead;’ however, some degree
of reflectivity, even though it may not be perceived as such, will be beneficial.
Discrete reflections are likely to be a problem only if they clearly are displaced from the direct
sound in both time and spatial orientation. Side wall reflections are usually perceived by the listener
well within a time interval which does not allow them to be heard-as such. However, a reflection off the
back wall can rebound from the screen itself, creating a ‘round trip’ echo that may be delayed by as
much as milliseconds. The effect here is to render dialog difficult to understand. In older cinemas
with balconies, such reflections were often generated by the balcony front (or fascia) itself. Substantial
acoustical damping had to be placed on that surface in order to diminish the problem.
In most cinemas constructed today, echo problems can generally be dealt with by ensuring
that the back wall is very absorptive and that substantial damping is installed behind the screen on the
baffle adjacent to the loudspeakers.