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Fluting closed body


Salve Håkedal

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I do the fluting work after I close the body, but before attaching the neck. I like to have the post in while I do this work, so I can listen to its sound at an early stage in the construction and see if I can build up a better feeling for what produce a good fiddle.

For some fiddles now, I've also recorded knocks against the belly at the left bridge foot position, and made spectra plots to (try to) aid in understanding what's happening. My recording method is rather crude, so small details can't be counted on. There is too much variation from knock to knock..

Knocking on the hardanger fiddle I currently work on, does however show something that is so clear that it must come from more than my sloppy method:

Just above 1000Hz there is a drop in amplitude after fluting the belly. When the back is fluted, that drop dissapears again.

So here is one more graph from Norway, this time from an acoustic amateur.

Who knows.. this may be of some interest to some of you.

post-29099-0-10785400-1311341739_thumb.png

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Interesting working method and data. I think we see that the signature modes have moved a little down in frequncy as well. Also interesting to see that the B1+ lie quite low around 500Hz, I think a typical trait of hardanger fiddles. I have assumed that the low B1+ might have been due to the larger neck, more weight in the pegbox etc. But this suggest that maybe that must be related to the body itself.

If that differnce above 1 kHz is real, that is a quite large difference. Also puzzling to see that the A0 apparently became weaker with the fluting, if we can trust that the overall excitation level is the same.

Seems like the B1+ was a little more influenced by fluting the back while the B1- seems to have moved more for the fluting og the top.

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You Oberlin regulars (or just plain others) who have experimented with the effect of the wings on violin sound...

Does it make any sense to you that fluting might be incorrectly attributed to an aesthetic purpose, where in fact it is the artifact of final voicing? That's to say, something to be done with the instrument strung up in the white and fine tuned for sound?

Best regards,

E

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To me it sounds more practical and likely that the sound from working on the fiddle, scraping, etc may give useful information either, concious or subconciously. It is very simple to put the soundpost in and do this, a smart approach and it can't slow down the work much either.

My personal assumption based on what I have read about the cremonese working methodes, it does not seem to be likely that they stringed up the fiddles in the white and voiced the instruments that way. That is the impression I get from reading e.g. Rodger Hargrave.

However, stringing up a fiddle in the white seems like a smart thing to do, If the time is available.

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..

Also puzzling to see that the A0 apparently became weaker with the fluting, if we can trust that the overall excitation level is the same.

..

The overall excitation is not reliable with my method.

Is it a black alder back on that fiddle body, or is it maple?

Maple. ~.58g/cc. The fluting in the back is quite wide. (It's more narrow in the top.

Except for the ff area, the archings are not very different from a "standard" violin.)

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A little while ago I posted some results where I compared the same violin body with two different top plates, one of Douglas fir and the other of Hemlock. The plates had been tested with fairly heavy edges, about 0.5mm thicker (on average) than I would use on a violin that I intended to sell. To see if these heavy edges were having a strong influence on the violin, I tested it both with the thick edges and with the edges at normal thickness. As you can see, its sound output with thinned edges was a little bit less but the 1200Hz region is proportionally stronger after the thinning.

In my tests I am correcting for the strength of the tap on the violin body, I calibrate the system between measurements to account for drift in the microphone recording levels that I had seen in earlier tests, and I also test with the soundpost in five different positions to minimize the effect of placing it in just one position. I'm not exactly sure how good my amplitude calibration is yet but I think it's good to better than 1dB, however I'm still not sure how many different soundpost positions would need to be used in order for that level of measurement. In principle that is easy to test, but very, very boring to do in practice.

post-24240-0-85011700-1311632509_thumb.jpg

post-24240-0-58621800-1311632534_thumb.jpg

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A little while ago I posted some results where I compared the same violin body with two different top plates, one of Douglas fir and the other of Hemlock. The plates had been tested with fairly heavy edges, about 0.5mm thicker (on average) than I would use on a violin that I intended to sell. To see if these heavy edges were having a strong influence on the violin, I tested it both with the thick edges and with the edges at normal thickness. As you can see, its sound output with thinned edges was a little bit less but the 1200Hz region is proportionally stronger after the thinning.

In my tests I am correcting for the strength of the tap on the violin body, I calibrate the system between measurements to account for drift in the microphone recording levels that I had seen in earlier tests, and I also test with the soundpost in five different positions to minimize the effect of placing it in just one position. I'm not exactly sure how good my amplitude calibration is yet but I think it's good to better than 1dB, however I'm still not sure how many different soundpost positions would need to be used in order for that level of measurement. In principle that is easy to test, but very, very boring to do in practice.

Hi William:

would you mind describing the plate thicknesses at the minimum of the fluting and how far inboard the minima lie? If you don't want to, no problem.

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Off the top of my head I don't know. The thickness of the wood where the top meets the linings is thicker than I typically use in spruce violins but due to the results of this test, I might be decreasing the amount of fluting that I use on new violins. I say that I might because I'm not completely sure how to interpret this result yet. Does it mean that violins with thinner edges are less loud or does it mean that you just have to bow it a little harder to get the same volume but that it will have the same maximum output when played very hard? For equal bowing pressures, positions, and speeds, the violin with thicker edges would've been louder but that isn't automatically a good thing and isn't the full story. I suspect that the maximum sound output from a violin is going to be determined mostly by the bow-string interaction but at least around the body resonances the violin's body will play a role too.

I'll post information about the fluting when I have time to tinker with this violin a bit more. I'll probably reduce the edge thicknesses more to see if the trend of thinner edges leading to less output continues.

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The external arching on this violin is continued out to approximately as far as the inner surface of the linings, no scoop or channel. So the thickness of the top plate at the lining gluing surface will be fairly thick, ~4mm. I think for the next set of tests I'll retest the violin in its current start to make sure nothing has changed (edges coming unglued...), then add a 0.5mm channel on the outside of the plate and retest, then reduce the edge thickness by 0.5mm .

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The external arching on this violin is continued out to approximately as far as the inner surface of the linings, no scoop or channel. So the thickness of the top plate at the lining gluing surface will be fairly thick, ~4mm. I think for the next set of tests I'll retest the violin in its current start to make sure nothing has changed (edges coming unglued...), then add a 0.5mm channel on the outside of the plate and retest, then reduce the edge thickness by 0.5mm .

Thanks, William. please post results of changes.

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A little while ago I posted some results where I compared the same violin body with two different top plates, one of Douglas fir and the other of Hemlock. The plates had been tested with fairly heavy edges, about 0.5mm thicker (on average) than I would use on a violin that I intended to sell. To see if these heavy edges were having a strong influence on the violin, I tested it both with the thick edges and with the edges at normal thickness. As you can see, its sound output with thinned edges was a little bit less but the 1200Hz region is proportionally stronger after the thinning.

This is what I would expect as a result. Higher frequencies require lower inertia / lower mass to allow the mass to react quickly enough and move to the input energy.

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