Cy Shuster wrote: > > Certainly it's typical to make Chladni patterns by applying a series of > vibrations, such as with a violin bow, or mechanical inputs of a certain > frequency. But I think you have to admit that hitting the board even a > single time is just a subset of the case where you hit it 440 times a > second, isn't it? A single hammer blow to a string still makes it > vibrate... The analysis of the board's response to a single blow should > just be one case of its response to multiple blows. > Perhaps... but I dont know why anyone would do so when at best the results will be vague and confused. Especially in light of the fact that you can simply excite the board to a resonant frequency and get the pattern for the corresponding mode so easily. In any case, I am still unconvinced that Steingrębers procedure for assuring a stiff boarder line on the edge of the sound board has anything to do with Chladni patterns. If this in fact displays the lowest resonant frequency of the panel, or fundamental mode, then I am wrong. But I'd like to see this confirmed. Especially when Steingręber himself discounts any connection. I would suppose he'd know the difference. > What I was really trying to learn (as I'm still learning) is what > Steingraeber was trying to accomplish by using the sand on an installed > soundboard, and hitting the bridge with a hammer (why not hit some keys, for > example, on a completed piano?). You said they were looking for where a > line of sand accumulated near the board's edges. Why? The line of sand accumulated near the board's edges represents a stiff area... i.e. it does not vibrate readily when the sound board is banged by a single blow with a hammer. Whether such and area necessarily relates to one or more resonate mode or not is another issue. In any case he wants evidently a very precisely defined stiff border that follows very closely the exact physical borders of the sound board. > > My point of raising the Chladni patterns is that it seems you could make all > kinds of different patterns appear in the sand, depending on where you hit > the bridge and how hard. So they must have a certain way they do things, > which gives them repeatable results. One way or the other, for a particular pattern to resolve the panel has to vibrate at that patterns corresponding resonate frequency. That's the only way that particular modes stiff points will be stiff, and the rest of the board moving. Tap tones are used in violins I've heard, I suppose you could do that, but those are more specific tones as opposed to some broadband bonk :) . Seems easier though to just identify the frequencies and use a vibration generator. > > This is another one of our ongoing cases of trying to take well-established > field methods, and look at the theory behind it to see if we can figure out > why it works... > > Thanks, > Sure is. :) Cheers. > --Cy Shuster-- > Rochester, MN > > _______________________________________________ > pianotech list info: https://www.moypiano.com/resources/#archives -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway mailto:rbrekne@broadpark.no http://home.broadpark.no/~rbrekne/ricmain.html http://www.hf.uib.no/grieg/personer/cv_RB.html
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