Microphone frequency response bandwidth
- Thread starter AndTripp
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Help Support GroupDIY Audio Forum:
The capsule is the main limiting factor - amplifier sections are MUCH easier to make behave.
An exception is the u87 amplifier, where top end is attenuated to linearize capsule.
Jakob E.
An exception is the u87 amplifier, where top end is attenuated to linearize capsule.
Jakob E.
The lower limiting frequency of the capsule depends on the venting. Consider that the mic has to work when it's different weather outside. The pressure behind the membrane must be equalized, but not too fast, or the membrane wouldn't move.
The capsule bias resistor and the capsule would make another first order hi pass.
I can't really help with HF.. Much more complex.
Edit:
Mass/spring system dynamics of the membrane are important. Can be modeled with an LCR low pass filter.
Google 'microphone handbook bksv' for my employer's wonderful exposition on the subject. Very good reading.
The capsule bias resistor and the capsule would make another first order hi pass.
I can't really help with HF.. Much more complex.
Edit:
Mass/spring system dynamics of the membrane are important. Can be modeled with an LCR low pass filter.
Google 'microphone handbook bksv' for my employer's wonderful exposition on the subject. Very good reading.
> the capsule, or the mics preamp? ...I realize this might be a fairly basic question
As Jakob says:
It's well-known that tubes and transistors can be designed to work from DC to MHz. (OK, simple hi-gain tubes fall at 50KHz or somewhat less, but supersonic.)
So any limit at *EITHER* end of the audio band is either design decision, or capsule limits.
Everything has a treble limit. There's no magic in passive devices (the capsule), they work with the small stray power from sound waves, so there is a trade-off between bandwidth and output level. Electronic gain is cheap, but everything hisses, so output level is really signal-to-noise level.
Directional mikes always have a bass limit related to their size.
True pressure mikes don't, but as Victor says the day-to-day-barometric (or slam-the-trunk) pressure change is FAR greater than musical sound pressure changes. If the diaphragm is soft enough to move with the music, it will collapse in high/low baro changes, so we vent it around a few Hz.
The DC network and capsule capacitance form a high-pass, but with FETs 5Hz is normal, lower is not hard. To go a lot lower, RF techniques go to DC.
Measurement mikes are available with response below 0.01Hz and above 200KHz (not in the same capsule), if that is what you are looking for. (The super-low range mike has a stopper for the baro-vent.)
As Jakob says:
It's well-known that tubes and transistors can be designed to work from DC to MHz. (OK, simple hi-gain tubes fall at 50KHz or somewhat less, but supersonic.)
So any limit at *EITHER* end of the audio band is either design decision, or capsule limits.
Everything has a treble limit. There's no magic in passive devices (the capsule), they work with the small stray power from sound waves, so there is a trade-off between bandwidth and output level. Electronic gain is cheap, but everything hisses, so output level is really signal-to-noise level.
Directional mikes always have a bass limit related to their size.
True pressure mikes don't, but as Victor says the day-to-day-barometric (or slam-the-trunk) pressure change is FAR greater than musical sound pressure changes. If the diaphragm is soft enough to move with the music, it will collapse in high/low baro changes, so we vent it around a few Hz.
The DC network and capsule capacitance form a high-pass, but with FETs 5Hz is normal, lower is not hard. To go a lot lower, RF techniques go to DC.
Measurement mikes are available with response below 0.01Hz and above 200KHz (not in the same capsule), if that is what you are looking for. (The super-low range mike has a stopper for the baro-vent.)
