I suppose you could connect an inductor across the microphone. You would need a DC blocking capacitor in series with it. This forms a series tuned circuit but with a large capacitor, the resonant frequency could be so low as to be irrelevant. But the inductor would need to be a pretty high value. Let's assume a circuit resistance of 1k and a -3 dB frequency of 723 Hz as before. So X
L needs to be 1000Ω at f = 723 Hz.
X
L = 2 pi f L
L = X
L / 2 pi f
= 1000 / (2 × pi × 723)
= 0.22 H
So you would need a 220 mH inductor. Digikey have one that would probably be suitable:
http://www.digikey.com/product-detail/en/70F221AF-RC/M8397-ND/774937
Let's calculate the resonant frequency if we put a 1000 µF capacitor in series with it.
f
R = 1 / 2 pi sqrt (L C)
= 1 / (2 pi × sqrt (0.22 × 0.001))
= 11 Hz approx
So if you connect a 1000 µF capacitor and a 220 mH inductor in series, across the microphone, you will get the following behaviour if you play a frequency sweep with decreasing frequency.
At audio frequencies, the 1000 µF capacitor has a reactance of almost zero, i.e. it's practically a short circuit to the audio frequencies, so they only see the effect of the inductor, which will give a single pole high pass response with a corner frequency around 723 Hz. That means that signals above around 1 kHz will not be attenuated much, and a frequency of around 723 Hz will be attenuated by 3 dB.
As the frequency drops, the attenuation approaches a single pole high pass response of -6 dB per octave; that is, for every halving in frequency (one octave downwards is half the frequency), the attenuation increases by another 6 dB (well, 6.02 dB actually but 6 dB is close enough).
As the frequency approaches 11 Hz, the response of the combined circuit will be increasingly affected by the capacitor, and at 11 Hz the series circuit will hit resonance and will attenuate the signal to almost nothing. Below 11 Hz the response will pick up again as the reactance of the capacitor dominates the circuit's overall response.
EvenAR, I don't know whether this would be useful to you! You could try it and let us know how it goes.
