Electrical – Impedance and frequency response


Was reading the following:
"In order to deliver its full frequency response, a ribbon microphone needs to see an input impedance of at least 4-5 times its output impedance. For example, if a microphone has an impedance of 300-Ohms, the preamplifier should have an input impedance of 1200 to 1500 Ohms, or greater"

Why would lower impedance input on the mic preamp attenuate frequencies? I'm assuming high frequencies are attenuated?

Best Answer

Ribbon microphone: -

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Firstly, if you load the transformer output too much the high frequency response will be reduced because of parasitic inductances in series with each winding. But there's a more fundamental thing that happens.

The ribbon is moved by changes in air pressure i.e. it is an electrical generator hence too much load current from the output mechanically dampens the ribbon and alters its frequency response.

Information: Ribbon Microphones