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Capacitance linking to phase shift

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Apr2-11, 06:42 AM
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Hi, I'm looking for an equation which links capacitance to the phase difference between two microphones (picking up audio from a loudspeaker). (the speaker gives off a signal at 3 kHz).

My experiment, at the end of the process, was devised to be linked into the setting of microphone positions on a kick drum of a drum kit. For example, if two microphones were used, there would be a phase difference between the two signals into the mixing desk.
As such, Iím representing an approximate frequency of the drum kit with a signal generator attached to a loudspeaker for ease of use in a physics lab. Therefore, I was hoping that using a capacitor in series with microphone A (closest to the speaker), I could add a phase shift to produce constructive interference and therefore remove the phase difference between microphone A and microphone B.
I was therefore hoping that there may be an equation linking either phase difference, distance from the loudspeaker, frequency or wavelength to the capacitance required to shift the phase of A to produce constructive interference.

Any help apprectiated,
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Apr2-11, 08:03 PM
Sci Advisor
P: 4,016
You really need something that would produce equal phase shifts at different frequencies.

A capacitor will not do that since it has different impedances at different frequencies. So, it would produce severe changes in the frequency response of the microphone.

The main cause of phase shift would be the different distances sound travels to get to each microphone.
Since these sources are producing different sounds, any interference between them should be minimal.
Beats etc will still be produced, even if you got the microphones exactly equally spaced from the instruments. They would just be slightly displaced in time.

There used to be devices called "bucket brigades" which would delay a sound for a second or so to produce echo effects. I doubt if you could still get them.

These days, you could record each microphone's output and then cut and paste the putput on a sound editor in a computer to produce whatever effects you like.
Not so easy for a live performance, of course.

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