Symetrix 571 SPl, Руководство пользователя

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Calibration: Special Cases Appendix A
Circumstances occasionally prevent the installer from calibrating the 571 in a quiet environment,
even though it may be known that the ambient noise does, in fact, sometimes fall to a known value.
To artificially create the input level that would be seen by the 571 when the room is at its quietest,
place an in-line pad in the sensing microphone input(s).
For example: a factory environment runs at 92 dBA continuously. Occasionally the ambient SPL
drops to 67 dBA. This represents a difference of 25 dB. Prior to calibration, insert a 25 dB in-line
pad into the microphone line. Perform the calibration procedure, with the S
ET
L
EVEL
M
IN
and S
ET
L
EVEL
M
AX
controls set for an output level range of at least 25 dB. When calibration is complete,
remove the pad.
Assuming that the 571 were operating at a ratio of 1:1, the gain would go up 25 dB when the pad
was removed. Conversely, the gain would, as a result, be able to go down 25 dB when the noise
dropped. Without the use of the pad during calibration, the 571 would never know that the ambient
noise level could go that low. As a result, its operating range would have been seriously restricted.
For safety installations that require the system to operate at a specific minimum and maximum SPL,
use a sound level meter in the environment during the calibration procedure. Simply adjust the S
ET
L
EVEL
M
IN
and S
ET
L
EVEL
M
AX
controls to deliver the output level required to develop the specified
SPLs.
Note When a minimum operating level is specified, do not allow user control of the O
UTPUT
G
AIN
T
RIM
function. Although the 571 will never allow signals to go above the set
maximum, it will allow signals below the set minimum if the O
UTPUT
G
AIN
T
RIM
is set below “0”.