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Bedrock SMxx operating manual
© Bedrock Audio BV, 2019
10. Other modules and control modes
10.1. Calibration
The Bedrock SMxx, the instrument itself as well as the microphone, is calibrated before
leaving the factory. A calibration certificate is included with the device. However, it is rec-
ommended that you carry out your own “user calibrations” from time to time, especially
under the following conditions:
•
You are using the device considerably above or below room temperature
•
You are planning to use the device again after a prolonged period of storage
•
You are planning to do measurements for which a high degree of accuracy
is required, e.g. certification measurements
Reference sources (calibrators) are available from a number of vendors. These generate a
test tone which is adaptively adjusted to a fixed, accurately know signal level (usually 94.0
dB). This makes calibration relatively easy: insert the microphone tip into the port of the
calibrator, using an adapter with suitable dimensions for the microphone tip. The device
should now measure the nominal signal level produced by the calibrator. For the SM30/
SM50, Class 2/Type 2 calibrators are recommended (such as the Cirrus CR:514), for the
SM90 we recommend a Class 1 /Type 1 calibrator (e.g. the Cirrus CR:515).
The Bedrock SMxx can be calibrated with any stable sound source of a known reference
level. This can be a calibrator, but a other non-fluctuating sound field will also work.
Calibration module while measuring a 1 kHz calibration tone (left) and once the calibration
factor has been calculated at the end of the procedure (right).
When calibrating the SM90 with BAMT1 microphone, correct the nominal
value of the calibrator (typically 94.0 dB) with -0.1 to account for the free
field response and other correction factors.
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