audio
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?
Carbon mic's were pressure controlled resistive devices that produce variable current when driven by a voltage source. They had poor frequency response but the side tone could be cancelled out or adjusted to a minimum easily, so your own voice was minimized on your earpiece. (sidetone) But the freq response was as it is defined 400~3.2Khz today. with 8kbps digital rates present day telephony is limited by a 7th order "brick filter" at 4KHz to satisfy requirement to block all image signals> 4kHz.
I do not have curves for skirt steepness on carbon mics.
The top trace is a perfect output for a differentiated square-wave:
The \$C\$ is your coupling capacitor. This is a high-pass filter with
\$ f_c = \dfrac{1}{2 \pi RC}\$
So the higher RC the lower the cutoff frequency. If \$f_c\$ is lower than the signal frequency the signal will pass without much distortion, that's the rightmost waveform. As RC becomes lower the cutoff frequency will move to the right, and ultimately only the signal's highest frequency components will pass the filter. That's the leftmost waveform, only the edges will pass.
So to get a good reconstruction of your signal you'll have to increase RC. I'm not quite sure where exactly you measured this signal, so I don't know the components' values, but you may increase \$R\$ by a factor 10 to start with.
Best Answer
Ribbon microphone: -
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