Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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"Have I thought this through correctly ....."

Posted by 13th Duke of Wymbourne (A) on November 23, 2021 at 19:07:32

In Reply to: IM, absolute polarity, and recording posted by psn on November 19, 2021 at 13:08:24:

I think no, and I think that doppler shift is a red herring. The two different frequencies combine to make a time domain waveform that is their combination and encompasses their phase and amplitude relationship. That is what the speaker reproduces, or what a microphone would capture. If that time domain waveform is asymmetrical then it will be captured/reproduced differently if the system polarity is changed. In your experiment I suspect the waveform is symmetrical, though musical transients can be asymmetrical.

Intermodulation distortion is generated by the same mechanism that produces harmonic distortion when you pass more than one signal through the distorting mechanism. As well as each tone generating its harmonics, new non-harmonically related tones appear dependent on the difference frequency. Intermodulation would not be produced by a speaker cone producing 70Hz and 1100Hz simultaneously unless one, or both tones, is large enough to make the cone move non-linearly.

Regards,
13DoW

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