AUDIO Stereo PHASE DETECTOR
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Designed and Built by Charles Kitchin of Analog Devices Norwood, MA.
Audio Phase Detector For the owners of a modest stereo system utilizing one speaker per channel, phasing the speakers is a relatively easy task. By connecting the speakers by polarity dots or switching the leads from one speaker and listening for the most solid bass response and best stereo centering, proper phasing is accomplished.
However, if more than one amplifier is used such as in biamp and triamp systems, phasing can become a horror show. Unless the amplifiers are identical (i.e.,the same phase shift in each), wiring up the speakers by polarity will not work. The problem is compounded by the electronic crossover which may, or may not, have the bass, midrange, and/or treble outputs in phase with another. Also microphones and audio lines are difficult to phase correctly.
A simple and inexpensive solution to this problem is to send a coded signal through the system. It is picked up on a portable receiver which can listen to each speaker individually and indicate its phase relative to the other speakers in the system. Such a device is the audio phase detector. The coded signal is a sawtooth waveform generated by an integrated circuit voltage to frequency converter (a voltage-controlled oscillator), the Analog Devices AD537. A sawtooth waveform is connected to the line input jack of an amplifier, amplified, and the speakers will produce the waveform into a sound wave picked up by a microphone on the receiver. The air mass between speaker and receiver acts like a capacitor and differentiates the waveform. So in practice, the high amplitude spike can be detected, and it's polarity will be due to the relative phasing of that particular speaker. NOTE: Reasonable offers considered as well.
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