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The specifications for C-2 and the C-4 mics are identical, except for:
Open circuit sensitivity  = 41dBv for the C-2, and -38 dBv for the C-4
 Max SPL  = 140dB when the -10 switch is off,  and 150 dB when the -10 switch is on,  Max SPL = 136dB when the -10 switch is off, and 146dB when the -10 switch is on.