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20log(7/4) = 20log1.75 = 4.86dB
So the sound pressure level at mic will be
100 – 4.86 = 95.14dB SPL.
We know that 94db SPL corresponds to 1Pa of pressure, and on this mic 1Pa yields -46dbV. The sound pressure level at mic is 95.14dB SPL, which is
95.14 – 94 = 1.14dB SPL
more. This means that there will be 1.14dBV more on the mics output also.
-46 + 1.14 = -44.86dBV
Between the mic and mic preamp there is a 10dB loss on mic pad, so the input to the preamp will be
-44.86 – 10 = -54.86dBV...