Use of a smaller opening would be the first strategy for getting higher Q. Making sure that the walls of the vessel were solid reflectors would be an important factor, too.
I noted that several of his sustained oscillators were basically either relaxation or blocking oscillators, neither of which is noted for good phase noise performance. Even the pendulum clock mechanism was interfering severely with the pendulum's motion- if you look closely you can see that the pendulum bob's position versus time function was a severely clipped waveform. The flex hose demonstration was interesting in that different regimes of swinging speed resulted in oscillation in different modes. I wonder why. But in hearing people learning to play different musical instruments, mostly wind instruments but also including the violin, I was once moved to say that playing these devices the art was in making an oscillator run in a resonator mode other than the "natural" one. For an interesting look at oscillating modes and a really oddball sustained oscillator, view https://www.youtube.com/watch?v=m6631u7d4E0. and/or google "mercury beating heart". The electrochemical effect makes the blob oscillate between a hunched-up shape and a flattened shape. If given time, this hunching oscillation "pumps" a degenerate parametric oscillation between the two triangular shapes at nominally half the rate of the original oscillation. I first saw this demonstrated in high school, but the demonstrator also could not get a sustained oscillation. I thought about that for a while and decided to try a little external stimulus in the form of low voltage DC from an external supply. After a little optimization it worked beautifully and could run for hours on end with little of no attention, giving me the luxury of trying a range of different blob sizes. With different sizes I could get sustained parametric oscillation in four different modes: 2-sided, 3-sided (as seen in the You-Tube clip), 4-sided, and with difficulty even 5-sided. Of course I didn't really understand what was going on at the time, and didn't arrive at the parametric oscillation theory until years later. BTW, I used a baking soda solution instead of a chromium-based chemistry, and an electrode coming down from the top center, with a large ring surrounding the mercury blob as the other electrical connection. Solution concentration, voltage, electrode tip height, and electrical polarity were the parameters that had to be adjusted for best performance. A mercury blob about one cm across in its resting state seemed to be a good starting point. For polarity, use the one that results in the blob's hunching up when the electrode tip is gradually lowered into contact with the blob. If the other stuff is not too far off, it will quickly take off oscillating at that point. I've been wondering whether this could be made to work with Galinstan obtained from modern-day clinical thermometers, instead of that dreaded mercury. A worthwhile experiment to try. I never did get around to measuring the Alan Variance of one of these oscillators; indeed, I didn't even hear of the concept until years later. It's probably not up to Time-Nuts' standards. Dana On Fri, Dec 8, 2017 at 4:59 AM, Hal Murray <[email protected]> wrote: > What's the Q of a Helmholtz Resonator? What do I do to make a high(er) Q > version? > > With a narrow band filter, it might make a neat demo/toy to pull an audio > signal out of the noise. With 2 at different frequencies you could > demonstrate FSK. > > -- > These are my opinions. I hate spam. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
