|MadSci Network: Physics|
I've googled around and can't find much on sub harmonics. I turned a thin steel ring from a pipe on a lathe at work. The ring is about 8 ½ cm in diameter, about 4mm thick, and about 4mm wide. The speed of sound in steel is about 6000 meters per second. I was wondering if I could induce sub harmonic resonant vibrations in this steel ring. My plan was to suspend the ring via a magnetic suspension, and then to excite it with a small electromagnet at some sub harmonic frequency (say, at 1/2 the fundamental, ~ 11 kHz). Record the sound coming from the ring, and perform an FFT on the recording to get a frequency power spectrum. However, I was never able to fabricate a magnetic suspension system which could “float” my ring. The path length of my ring is approx: c = pi * d ~ 27cm = 3.14 * 8.5cm. At 6000 meters per second, my fundamental frequency should be close to: 6000m/sec / 0.27m = ~ 22 kHz. As different from a “stretched string” supported at two end points, in which case there are no frequencies smaller than the fundamental. I suspect that I should get not only integer multiples of the fundamental, but because the system has no end points, also fractional harmonics – 1/2, 1/3, 1/4… I can “tap” the ring and hear frequencies that I know are less than 22 kHz. My question is: “Does anyone know if I should get sub harmonic resonant vibrations in such an experiment?” Thanks much in advance, ~Randy
Re: Sub harmonic vibrations – In a thin steel ring?
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