94 Bedrock SMxx operating manual © Bedrock Audio BV, 2019
A3. BAMT2 microphone
The BAMT2 is the standard microphone-preamp combination bundled with the Bedrock
SM30 and SM50 The BAMT2 is a highly stable 1/4” Class II / Type II electret microphone.
A3.1. Typical pressure field to free field corrections for the BAMT2
The correction factors below are added to the measured values to arrive at the expected
free field sound pressure level measurement when using the B&K4226 multi-frequency
calibrator.
Frequency BAMT2
31.5 Hz -0.3
63 Hz -0.3
125 Hz -0.3
250 Hz -0.4
500 Hz -0.2
1 kHz 0.0
2 kHz -0.5
4 kHz -1.2
8 kHz -6.5
16 kHz -5.5
A3.2. Typical free field response for the BAMT2
The typical free field response of the BAMT2 microphone is specified in this section. Note
that it is not feasible to perform actuator measurements with the BAMT2, as the micro-
phone capsule is not detacheable. For instructions on how to perform periodic calibrations
according to IEC-61672-3, which calls for a modified procedure for non-detacheable mi-
crophones, please refer to our manufacturer’s instructions in Annex B.
The table below specifies the typical free-field response of the BAMT2 microphone. The
typical free field response of the BAMT2 was measured by the manufacturer at 0 degrees
incidence, based on average values of microphone capsules against a B&K 4180 response
using a B&K 4228 Pistonphone.
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