Rolloff Frequency Calculations

[thomasraden]

I'm planning to build a bass rolloff circuit for my microphones.

Can anybody give me some values to use for the capacitors

for these following rolloff frequencies:

50Hz

100Hz

200Hz

The output from this circuit would be the mic input or the line

input of my MZ-NH700 unit.

Does this unit have different impedance load on the two inputs

making me having to use different capacitors for the different inputs?

Thanks

[Artstar]

I'm planning to build a bass rolloff circuit for my microphones.

Can anybody give me some values to use for the capacitors

for these following rolloff frequencies:

50Hz

100Hz

200Hz

The output from this circuit would be the mic input or the line

input of my MZ-NH700 unit.

Does this unit have different impedance load on the two inputs

making me having to use different capacitors for the different inputs?

Thanks

←

How much roll-off do you seek? Half (=6dB cut)?

The equation for impedance (in ohms) is Z = 1 / (2*pi*freq.*capacitance (in Farads))

Now assuming the mic input is around the 1kOhm impedance mark, to halve the desired frequency into the MD would mean throwing in a further 1kOhm in the chain. So in that case, you would then plug in the value of 1000 for Z and your desired frequency in the freq. variable. The result will be:

1000 = 1 / (2*pi*50*C)

1000*2*pi*50 = 1 / C

C = 1/100000*pi

C = 3.18uF

So proportionally, for 100Hz it would be 1.59uF and for 200Hz it would be 0.80uF.

[thomasraden]

Thanks for the answer. Does it matter if bipolar capacitors or normal electrolyte /tantalyte capacitors with polarity are used?

[Artstar]

Thanks for the answer. Does it matter if bipolar capacitors or normal electrolyte /tantalyte capacitors with polarity are used?

←

Sure will as that would affect the DC power being supplied to the mics. My advice is that you definitely stick with bipolar.