SmartSMS User Manual Soft dB inc.
User Manual p. 27
5.4 Sound Level Meter and acoustical calibrator
Standard type 1 and type 2 sound level meters with an AC output can also be used to operate the
system.
Figure 19: Connection set-up when using a Sound Level Meter
Compared to the set-up using the Soft dB Precision microphone and IMIC pre-amplifier device
(section 5.1), the extension cable for the sound level meter on this set-up can be up to 500 ft
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(instead of 150 ft). As for this set-up, two people may be required to perform the calibration of a
medium or large installation.
Note:
The Sound Level Meter (SLM) recommended for use with the SmartSMS must:
1. Have a dynamic range of 70 dB
2. Be capable of measuring a noise level as low as 30 dBA
1- A SLM with a 70 dB of dynamic range is strongly recommended since it allows reference
sensitivity adjustment (usually done with a level of 94 dB) and background measurement
(usually higher than 30 dB) with the same dynamic range on the sound level meter (30 to 100
dB). If the dynamic range used during the reference sensitivity adjustment and the
measurement process is different, the user must specify the difference in the interface used to
adjust the sensitivity (consult appendix B Sound level meter with limited 50 dB of dynamic
range for more information).
2- A SLM that allows the measurement of a minimum level of 35 dB can also be used, but in the
case of a room with lower background noise, it could introduce errors of up to 0.5 dB in the
adjustment of the masking sound. It is not recommended, but it can be used.
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The extension cable can be of significant length, given that the signal provided by the AC output of the sound level meter is
pre-amplified and has a much greater amplitude than the signal coming from the Soft dB Precision Microphone.
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