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Relative Influence of Materials Compared to Arching


Wm. Johnston

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I've probably posted everything in this topic elsewhere on Maestronet over the past year but never in the same place. I thought that it be good to post some of the results that I've had with some experiments in order to show the relative sizes of the effects of using different arches compared to different kinds of wood for the violin's top.

The experiment testing out very different top plates on the same 4/4 violin was described here, http://www.maestronet.com/forum/index.php?showtopic=323718&st=0&p=503188entry503188 To summarize, I tested a Douglas Fir top and a Hemlock top on the same violin. The Hemlock top wieghed 18g more than the D. Fir top.

For my tests of different arches on the top, I carved two tops from the same board of Hemlock. Both tops had the same arching hieght at the bridge. One top plate was carved so that its long arch was flat between the upper and lower bouts and the other was carved with a very rounded long arch. This was tested on a 1/2 size violin body because that was what I was playing with at the time.

Attached are the plots comparing the sound output for these two tests. Even if you don't know much about what these plots mean the important thing to notice is that one one plot the two test configurations have lines close to each other. In the other plot the lines are very far appart. The conclusion that I draw from this is that the arching is a very big deal. Materials are important too but you can play with arching and thicknesses to account for a lot of it's effect.

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The conclusion that I draw from this is that the arching is a very big deal. Materials are important too but you can play with arching and thicknesses to account for a lot of it's effect.

Wow! 10db between 2500 and 4500Hz. It appears to me that there is an approach to increasing projection in those results.

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One thing that Bellini mentioned to me was that everyone is always talking about thickness. He varies arching as an adjustment for wood. He even measures total arching height in tenths of a mm.

He is making a copy of the Plowden. When I asked him when he thought of this new model for him. He said I am not sure about what I am going to do with the arching.

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Wow! 10db between 2500 and 4500Hz. It appears to me that there is an approach to increasing projection in those results.

For this piece of wood it's obvious which arching I would use all the time except there are a few things to worry about. Sure it produces more high frequency output which would result in a brighter tone, more projection, and quicker response under the bow but it might feel stiff or hard to play too. It might not be the case, for all pieces of wood, that a rounded long arch will always produce this much more high frequency output than a flat long arch. I've only tried this out on one board of Hemlock that most violin makers would turn their noses up at, results might be very different for low density, high stiffness spruce.

When I had the violin body assembled with the flat arch and the round arch tops they felt like completely different violins in my hands, not surprising since their response to impulses are so different.

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Interesting thread and results. But I have a hard time believing that you get a 10dB difference in the signature mode region just by the shape of the longitudinal arching while the plates are equally thick. If the plot is made using a log scale for the frequency it will be easier to asess I think. 10dB extra in the frequency region above 3kHz is going to sound pretty harch.

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Interesting thread and results. But I have a hard time believing that you get a 10dB difference in the signature mode region just by the shape of the longitudinal arching while the plates are equally thick. If the plot is made using a log scale for the frequency it will be easier to asess I think. 10dB extra in the frequency region above 3kHz is going to sound pretty harch.

It's possible that this is some sort of artifact due to my measuring system, but the <400Hz amplitude looks pretty close for both cases. Perhaps some sort of artifact that only shows up at high frequencies? I don't think so but I haven't tried to prove that it couldn't happen. I have done a lot of other tests and this is the only variable that I've found that has had this much of an effect, if this was a problem in my testing system I would've expected it to show up in some other measurements too. Like I said before, just from tapping on the violin with my fingers and handling it I could tell that the flat arch and round arch were behaving very differently. While that is a very subjective test it seems to be in agreement with what was measured.

Keep in mind these violins were tested without a bridge and with a vertical excitation, both of which will increase the amount of high frequency output compared to the more normal case of a violin tapped horizontally on the bridge. I would not compare these plots to those of other violins tested in a different manner. Perhaps rather than saying the round arched violin would be more harsh, it is probably safer to say the flat arched violin would be less bright and possibly dull sounding? Since I'm testing the violins in a different manner than is normal, it's hard to look at these plots and assign a tone to the violin. I'm really only interested in tracking the changes in output at the moment so this method works well.

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maybe youve found the reason that cheap german violins with this rounded arching sound so bad and excessively bright, i suggest you quit messing around with half size violins and try your experiments on full size unless your planning on building a lot of violins for 6 yr olds

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Ok, thanks, this seems reasonable, though. Is the A0 around 300Hz or so, the first peak we see?

Puzzling to see such a huge effect on the frequency of the B1- (or CBR) and on the level of what must be the B1+.

Yes, I gave it relatively small f-holes in an attempt to get the A0 close to where it would be in a 4/4 violin. Since in a 1/2 size violin the other modes are higher, this may be misguided and introduce regions on the violin strings that aren't well supported by any modes, ie. uneven tone. I think those two large peaks are the B1s.

Another thing to point out, this 1/2 size violin did not have a neck while the 4/4 one did. Perhaps with a neck the influence of the arching would be less? I don't think so but I don't have any proof of that.

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maybe youve found the reason that cheap german violins with this rounded arching sound so bad and excessively bright, i suggest you quit messing around with half size violins and try your experiments on full size unless your planning on building a lot of violins for 6 yr olds

You mean harsh like del Gesu, that's where I got the inspiration for the round arch.

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You mean harsh like del Gesu, that's where I got the inspiration for the round arch.

Ok round longitudinal arch is inspired by a del Gesu?

No, I do not think many violins have strong sound output in the region above 4kHz. But as you state that may be related to the bridge and the direction of tapping. A violin with a bridge tapped vertically will also have a stronger high frequency output than whan tapped horizontally.

But in addition to this, the string harmonics also will have a falloff cutting the highs. But still, I think 10dB difference in the very highs are going to make a large differne in the sound. ANd I do not think it will be pleasant. But could be wrong. Playing them will give a better insight.

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on any violin i think youre not looking for maximum output but rather a balanced output of highs to lows and you especially dont want super loud harmonics that are louder than the fundamental, these violins are sometimes called screamers in the trade, ps i would love to see a side profile of this del gesu you got this arching from, are you sure youre not thinking of johann del gesu, the german copyist

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on any violin i think youre not looking for maximum output but rather a balanced output of highs to lows and you especially dont want super loud harmonics that are louder than the fundamental, these violins are sometimes called screamers in the trade, ps i would love to see a side profile of this del gesu you got this arching from, are you sure youre not thinking of johann del gesu, the german copyist

Late Del Gesus. Don't know if they were originally made differently from other instruments, or if something caused the arching to sag less over time.

If an instrument has high output over the entire spectrum, it's not hard to mitigate the highs with adjustment. If the highs are high and the lows are low, killing the highs won't do much good. Would that describe a cheap German or French instrument, perhaps? That's just conjecture for further debate, haven't had much exposure to them lately.

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A quick scan of the Bergen exhibition catalogue shows a huge variation in the long arches of some late GdGs - perhaps more than one would expect from movement (unless some were kept in a Turkish bath and others in a silica bag).

Pretty hard to know what they were like originally, what with string tension pushing them one way, and restorers taking a guess about how far to push them back the other way. Seems to be a trend in that group though, compared to other groups.

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Pretty hard to know what they were like originally, what with string tension pushing them one way, and restorers taking a guess about how far to push them back the other way. Seems to be a trend in that group though, compared to other groups.

I should have written more precisely.

I meant to say that most appear to have a smooth rounded top arch (Gregorowicz 1744, Sainton 1744, Ole Bull 1744, Doyen 1744 etc), and then there are a few that have pronounced bulges at the ends of the long arch (eg Donaldson 1742, Tellefsen 1742, Sauret 1743), which in the case of the Donaldson appears to touch the fingerboard.

The clustering of the years suggests some intentional experimentation of the long arching.

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At some point this is something that I would really like to do. It would take a lot of similar spruce from the same log to do it and I just don't have it at the moment.

A couple of years back I decided to get back into making in a 'serious' way and test the different-materials question. I jointed 13 backs and fronts, chose 4 closely similar backs from the same log and 1 from a different one, and 5 different spruces for the tops.

Now quite a way further (plates almost finished), I realise that I am not a good enough maker to control (keep constant) all the other variables beyond the materials. As a result, I am now relaxed and making a hotch-potch of what, I hope, will be good sounding instruments (with a little help from some friends).

C'est la vie.

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