15-24 Customizing Measurements Model 831 Manual
Care must be taken to ensure the decays are sampled
adequately and this can be evaluated using some simple
math. Consider that we have a reverberation time of 420 ms
for a 60 dB decay. 20 dB is 1/3 of 60 dB, so for T20, we
have 420 / 3 = 140 ms. Sampling at 5 ms gives us 140 / 5 =
28 data points. For T30 we have 210 ms or 42 data points.
Build Time is available when the method is set to
Interrupted Noise. The Build Time is the time the noise level
must be above the configured Trigger Level to sufficiently
energize the room. For example, if the Build Time is set to
five seconds, the sound source will be on for five seconds
plus the time it takes for the sound level to reach the trigger
level.
Use +20 dB gain only for Interrupted Noise since impulses
quickly exceed 120 dBZ.
Source Menu
Impulse Method
The RT-60 noise controls are
unavailable when using the Impulse
method.
FIGURE 15-32 Source Setting: Impulse Method
The impulse signal is generated externally, i.e., with a starter
pistol, a balloon, etc.; there is nothing to configure on this
page.
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