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Re: Motors as speakers?
Related to this, years ago, an NI customer was demonstrating what they make/control with LV. They make magnetic bearings for rotating shafts and are able to monitor and actively dampen all sorts of disturbances even large ones such as when a compressor turbine loses a blade. Anyway, the presentation included a magnetically supported aluminum shaft they'd attached small pieces of sticky putty to. The DSP controlled device compensated for the imbalance at several kRPM and charted the forces needed to balance onscreen. More impressively, when they shaved the material off with a business card, it rebalanced within a few milliseconds.
For the next part of the presentation, he spun the well balanced shaft to around 15 kRPM and attached a cable to something in his pocket. We sat there waiting for something to happen, and started to hear a buzzing that became somewhat rhythmic. It grew louder and changed in pitch, and then recognition set in. It was a Led Zeppelin intro and the dampening field they normally used to balance the shaft was now being used to drive the shaft to produce the acoustic signal. He had connected the cable to a walkman in his pocket, and the DSP was being asked to cancel that signal. The buzzing was the distorted guitar chords, and while the response if this "speaker" was anything but flat, it was good enough with the mid and high end of the spectrum that you could make out the song and everyone got a chuckle out of it.
Greg McKaskle
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