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Looper's Delight
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My son Eli and I studied the output of his singing bowl with a spectrogram. I overstated the bowls size in my earlier post. It is 117 mm outside diameter (about 4 9/16"), about 63mm high, rounded, and about 2mm thick at the top edge. The spectrogram allows us to see, in a scrolling chart, over time in the horizontal axis, the frequency components in the vertical axis, with the amplitude of each component indicated by shading. The lowest tone recorded was about 390 hz, approximately a G. The first overtone was at about 1070 hz, the next at about 1950 hz. These measurements are +/5.4 hz with the scale and tool used. The fundamental's amplitude is about 3db softer than each of the two overtones with the condenser mike used, when I strike the bowl with a thin stick. When the bowl is struck with a soft mallet, only the fundamental is visible on the chart, unless you keep hitting the bowl very hard. Where you hit the bowl with the hard stick effects the balance of fundamental and harmonics, but there are 3 primary tones. Making the bowl sing with a thick stick generates the same 3 tones. There is a pulsation of amplitude (beat frequency) for each of the 3 tones that varies in frequency with the speed at which I rub the stick around the bowl. I can make it beat very slow, maybe 1hz, to fast, about 8 hz, by the speed of circular motion. This beating adds much to the feel in my hand of the energy present. The beating is visceral. We attempted to match the tone by ear, to a synth patch that had fundamental and 2 harmonics (390hz,1170hz, 1950hz , fund, 3rd and 5th harmonics). We compared the audibly matched synth tone to the bowls tone in the spectrogram. The fundamentals matched in frequency. What we heard as tones in the bowl, matched what we heard on a minimal overtone synth oscillator. These sounds differ by the first overtone frequency. The synth has 1170hz (3rd harmonic) and the bowl has about 1070hz which is about 2.74 times the fundamental (390hz). We found no illusion between perceived pitch, and measure pitch with the 2 types of sounds. The beats in the rubbed bowl do change the character of the sound dramatically, however. I wish I had a large bowl to measure. If you want to view and measure the spectrum of a sound download Spectrum ver 5.1.7 (Windows only) http://www.mnsinc.com/rshorne/gram.html http://www.mnsinc.com/rshorne/gramdl.html It is a cool program, and shows a great deal about the character of sound. You just need a pc, soundcard, windows, and a microphone. regards, bret --- Ztars'R'Us <harvey@cts.com> wrote: > I'd think a crystal water glass would provide a clearer demonstration > and > analysis of the fundamental vibrational modes. Fairly uniform shape > and > wall thickness, and tighter more uniform crystalline structure than > the > hammered alloy. > -HS > > At 03:53 PM 10/18/00 -0700, you wrote: > >Is a 15" loudspeaker cone small? The 20" bowls vibrating surface is > >larger than the speaker size that is commonly used for generating > loud, > >low freq. I have casually mapped the vibrating surface and it seems > to > >be virtually the entire sides of the bowl, down to the start of the > >base. The bowl is small, but the radiating surface of the bowl > seems > >large to me. But small and large are relative terms, aren't they? > > > >Regarding efficiency, I cannot say how efficient the bowls are. As > you > >play them you constantly put energy into them. I make no claims for > >the bowls efficiency, but they could be inefficient (and per stated > >principles) and still be loud and low freq. It tires me to play > them > >for very long, but I'm not sure how to quantify the energy I put > into > >the bowl from the playing (how efficient is the energy transfer from > my > >hand to the stick to the bowls edge?). A single strike to the bowl > >will excite it at the low fundamental, if you hit it in the right > area. > > > >Anyway, I am very curious about what is happening, and sorry if this > >thread is wearing thin for some of you. I find the singing bowls > >fascinating and fun, and it is my nature to try and figure out how > >things work, especially sound (I too am an engineer, but acoustics > are > >only a part of my job with disk drive design). > >I'll shut up now, and see what I measure. > >bret > > > >__________________________________________________ > >Do You Yahoo!? > >Yahoo! Messenger - Talk while you surf! It's FREE. > >http://im.yahoo.com/ > > > > > > > http://www.starrlabs.com > __________________________________________________ Do You Yahoo!? Yahoo! Messenger - Talk while you surf! It's FREE. http://im.yahoo.com/