Bolymin BE905A2 User Manual page 51

Here list the recommended microphone specification when you try to find other one in
BE905A2:
 Microphone Sensitivity: -58±3dB (0Db=1V/ubar)
 Speaker Normal Impedance: 32Ω±15% at 1K Hz
Output S.P.L. :120dB±3dB

 Input Power: Rated - 2mW, Maximum -10mW
 Frequency Response: 20~20,000Hz
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Rev. V0.6