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#16
11-22-2020, 07:05 PM
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Thank you Allen. One difference between guitars and mandolins is that with mandolins the shape of the patterns stay pretty much the same no matter what you do, unless you do something really extreme. Extreme changes can risk structural failure.
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#17
11-23-2020, 02:06 PM
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redir asked:
"Are you saying that they actually did Chladni tests on Strad tops after removing them from the violin?" Yes; a few. At that time they were in the process of 'updating' many of the Old Master instruments, replacing the necks and bass bars, and sometimes 'correcting' graduations in the process. Savart seems to have gotten top and back plates from Vuillaume, who did much of that work, to test. It's not too uncommon to remove the top of a violin, but backs are another matter. "Are you saying that you run the Chladni test on the fully assembled guitar?" I do look at Chladni patterns on finished instruments, but only to see what they're doing. Part of the idea behind 'free' plate tuning for me is to try to avoid having to get in and modify completed instruments. My hand is too big, at least for reaching into Classical guitars, so it's much easier to work on things before they're closed up. I have used assembled mode information, as well as 'impulse' spectra, to make 'tonal copies' of a couple of older guitars; a '43 OM-28 and a Lloyd Loar L-5. Both were pretty successful, as far as I can tell. The Martin owner was looking for a guitar that sounded like his original that he could leave strung with mediums, instead of swapping them out with lights frequently, and he found the copy satisfactory. Sadly, we will probably not be able to get the copy of the L-5 together with the original, but the owner of the new one, who had played the original a lot, is satisfied. peter.coombe wrote: "One difference between guitars and mandolins is that with mandolins the shape of the patterns stay pretty much the same no matter what you do, unless you do something really extreme." Violin family instruments have such a standardized 'free' mode series that they just refer to them as 'mode 1', 'mode 2', and so on. Changes in the arch shape, graduation patterns, and bass bar, alter the shapes a bit, but almost never the relative order. Archtop guitars behave in much the same way as violins; so that you can use the same guidelines with good results. I have not done much work with mandolins, although we did have the top off a D'Angelico once, and looked at the modes. That was a long time ago, and my partner at the time may have those records. I do recall that the modes were well formed. Guitars are not so standardized. Classical guitar 'fan' bracing seems to produce a more or less standard mode series, at least for the low order modes (say, the first six or eight) which is altered a bit if you add in a Bouchet bar, or angled waist bar. Steel string guitars are a bit more variable. The normal Martin-style X brace is asymmetric, and it can be hard to get the modes to 'close' properly, especially on scalloped brace profiles. Dana Bourgeois' non-scalloped treble side bar improves the symmetry a lot, which I believe is the reason it sounds the way it does. I went to double-X bracing to get better symmetry, and it seems to work well. In the 'pair' experiment using 'standard' and 'double-X' bracing the preference at an ASIA symposium, though not strong, was 2:1 in favor of the sound of the double-X in blind playing tests.
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#18
11-23-2020, 03:58 PM
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Quote:
More here - http://petercoombe.com/publications/jaamim7.html http://petercoombe.com/publications/jaamim8.htm
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