scordatura

Christian Bayon's Bass Bar In the Feb. 18 Strad

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10 hours ago, Don Noon said:

The bass bar IS important, as evidenced by my test of what happens when you don't have one.

As long as there is a bass bar, the exact mass and stiffness (within reason) don't seem to be terribly important, from what I can tell.

 

19 minutes ago, Eryri said:

I'd say the violin is not working in the same way with this bar, so previous conventional bass bar experience may not necessarily be relevant.

I doubt that the ordinary player would be able to tell the difference. But I can be wrong?

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One thing that strikes me as a possibility, is a small increase in harmonic content in the higher frequency spectrum, due to the freed plates area between bass bar and top contact points. Those contactless areas should vibrate more, hence radiate more. Christian's method should add defined modes at wavelengths matching the gap lengths. 

IMG_20180201_121212.jpg

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2 hours ago, Torbjörn Zethelius said:

 

I doubt that the ordinary player would be able to tell the difference. But I can be wrong?

You have a point here. Better players tend to be more aware of small differences. If Lewis Hamilton gets into a Formula 1 car, he will understand what changes need to be made to extract the last few percent of performance out of the car. If the average person got into a formula 1 car, they probably would not even be able to get the tires and brakes up to temperature. An extreme example perhaps but illustrates the point.

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2 hours ago, Luis Martins said:

One thing that strikes me as a possibility, is a small increase in harmonic content in the higher frequency spectrum, due to the freed plates area between bass bar and top contact points. Those contactless areas should vibrate more, hence radiate more. Christian's method should add defined modes at wavelengths matching the gap lengths. 

I thought so too initially... but some rough calculations show that the first mode in the gap would be above the useful frequency range.  To me, this implies that it acts like a normal bass bar, although with a different mass and stiffness profile.

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I would be worried by the deformations of the top in the long term that could be accentuated by the areas left free, but I suppose that Christian knows what he does.
I would like to ask him : how long are you doing this kind of bassbar?
Just to know.

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1 hour ago, Don Noon said:

I thought so too initially... but some rough calculations show that the first mode in the gap would be above the useful frequency range.  To me, this implies that it acts like a normal bass bar, although with a different mass and stiffness profile.

Correct, even 1/4 wavelength harmonics are ultrasonic. I wonder what the center of mass further away from the top plate might do... Any thoughts?

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8 hours ago, Davide Sora said:
 
I would like to ask him : how long are you doing this kind of bassbar?
Just to know.

Since 3years on 30 instruments , some of them made before with traditional bass-bar, so it was interesting to try the same instrument with different bass-bar, violins and cellos.

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8 hours ago, Luis Martins said:

Correct, even 1/4 wavelength harmonics are ultrasonic. I wonder what the center of mass further away from the top plate might do... Any thoughts?

I disagree.  Laser vibrometry (1) has shown the top plate breaks up into small areas about the size of Christian's bass bar gaps which do effectively produce far field sound at high frequencies for conventional violins.

Since bass bars act as wave guides dividing the plate area into smaller areas having motions of different vibration phases I would expect that the gaps in the bass would not act as local wave guides so the pattern of nodes and antinodes could be quite different. Therefore the resultant sound would also be different.   

 

1.  "Laser vibrometry measurements of vibration and sound fields of a bowed violin", P. Gren et al., Measurement Science and Technology. 17 (2006) 635-644,

Violin vibrations and sound fields are shown at the violin's fifth harmonic at 1415Hz and the eight harmonic 2264Hz.  I would expect higher harmonics still within our hearing range to also show similar effects.

I'm sorry I couldn't reproduce their vibration photographs because of copyright restrictions

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1 hour ago, Marty Kasprzyk said:

I disagree.  Laser vibrometry (1) has shown the top plate breaks up into small areas about the size of Christian's bass bar gaps which do effectively produce far field sound at high frequencies for conventional violins.

I disagree with your disagreement.  Although I don't have the referenced paper, what I see in the Strad3D and my own modal mapping shows that the longitudinal spacing of the nodes and antinodes is larger than the bass bar gap, even for the higher end of the bridge hill region.  Crossgrain, things are naturally closer together.

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7 hours ago, Marty Kasprzyk said:

I'm sorry I couldn't reproduce their vibration photographs because of copyright restrictions

For the eternally curious, I believe the same paper can be found here at the very end of the thesis:

http://www.diva-portal.org/smash/get/diva2:991570/FULLTEXT01.pdf

I would be interested in seeing the ref'd animations (the links seem to be long-dead, but perhaps they point behind a publisher paywall instead). Have you seen these, or do you know of other places they might have been published?

 

And this thread has got me thinking: Should it be possible for someone to condfidently back-out important characteristics of the bass bar (or even reverse engineer one, I suppose), from a stand-alone analysis of (for example) this video?

 

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10 hours ago, Don Noon said:

I disagree with your disagreement.  Although I don't have the referenced paper, what I see in the Strad3D and my own modal mapping shows that the longitudinal spacing of the nodes and antinodes is larger than the bass bar gap, even for the higher end of the bridge hill region.  Crossgrain, things are naturally closer together.

I disagree with your disagreement of my disagreement.

I found a copy of 1414Hz sound field photograph that was in the article on the internet (Google search for "holographic violin" images) so I've attached it below. 

This same photo is also seen as figure 18.11 in the book "Why You Hear What You Hear" by Eric Heller.  Notice the white bar in the photo which shows the wave length in the air for that frequency sound.  The length of the vibration areas of the violin are shorter than the sound's wave length so you would expect that the violin would not produce much sound at that frequency because the different phases of those vibrating areas cancel each other.  However Heller points out that the antinode areas are asymmetrical so that some far field sound is still produced--we do after all hear something.

The bass bar acts as a wave guide which divides the plate areas into antinodes of different phases (blue and red in the photos) which would cancel the near field sound.  But the bass bar is off-set bass bar which makes the vibration patterns asymmetrical with different areas so this cancellation is not complete.

I wasn't able to find a free photograph for the vibrations at 2265Hz which shows that the antinodes are much smaller while their asymmetry is still apparent.  The antinode size is now more similar in size to Christian's bass bar gaps like I had mentioned earlier.  I would expect that his anitnode patterns would be altered for his violin's higher frequency vibrations therefore the violin's high frequency sound character would probably change too.

I would be wonderful if laser vibrometry could be done on Christian's violins too to see if their vibration patterns and sound fields were any different.  It would also be interesting to see their frequency response curves done by impact hammer tests.

 In any case Christian and his customers seem to like the results.

1415 b photo copy.pdf

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If you look at the longitudinal direction of the top, it looks like ~1 wavelength along the body on the bass bar side, and maybe 1.5 wavelengths on the soundpost side.  If you think you want a half wave (with fixed end conditions) happening in the bass bar gap, the frequency is going to be bunches higher than this.

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5 minutes ago, Don Noon said:

If you look at the longitudinal direction of the top, it looks like ~1 wavelength along the body on the bass bar side, and maybe 1.5 wavelengths on the soundpost side.  If you think you want a half wave (with fixed end conditions) happening in the bass bar gap, the frequency is going to be bunches higher than this.

I agree with Don on this. The gaps, per se, are way too small to affect top plate radiation of useful hf on the new open top plate areas. At least on a significant level when compared to contemporary bass bar design.

As Christian designed it, the bar should maintain its mechanical purpose regarding string tension, and act as a wave guide from the bridge to top and bottom areas of the top plate. However, the gaps and the elevated center of mass should allow a more pronounced twisting action on the bass bar, impacting A1 and B1 spacing and Q factor.

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2 hours ago, Luis Martins said:

I agree with Don on this. The gaps, per se, are way too small to affect top plate radiation of useful hf on the new open top plate areas. At least on a significant level when compared to contemporary bass bar design.

I don't think there is any special activity within the gaps... One can as well assume that the active area "starts" at one of the gaps and ends at the other...

Or... which is IMHO (though not scientifically supported) more likely is that the gaps represent less stiff areas of the bar (and thus of whole belly) compared to standard bar and PERHAPS ordinary bar with scooped areas where the gaps on Christian Bayons' bars are located would produce similar results. Think of how guitar braces are shaped... Steel string guitars with tapered braces sound consistently different from those with straight or scalloped braces... the exact shape of braces adds flavor. On guitars this can be much more audible because of the angle of braces and thinness of the flat top...

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Those modes varies over the whole spectrum that a violin can produce (let's say 200 - 7000 Hz). The gaps would not do anything (significant) else than reduce weight (not stiffness) at theese areas. Overall I see this as a heavier bass bar, particulary at the ends.

I do the opposite, reduce weight at the ends as much as I can without decreasing stiffness, i.e. optimizing the bass bar for minimum weight, keeping up stiffness. This is balancing on the edge of wolf at B1+, but very powerful bass/G-string that is somewhat difficult to play (bam, boom, less after ring and more difficult to play uppper positions)

 

 

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4 hours ago, Leo KUNG said:

eighth harmonic, 2265 Hz5a74c731d25d4_2265Hz.jpg.2c3d0e3ed7b770363f998ac772ebb519.jpg

Thanks Leo!

Attached is an older technique holographic black and white image (1) at 2000Hz for a different violin.  The antinodes don't show the phase differences but it does show that the vibrating surfaces breaking up into smaller and smaller regions.  I'm guessing the size of these regions get to be about Christian's bass bar gap size in the range of about 2500 to 3000Hz.  This is in the important "bridge hill" frequency range that good violins show an appreciable output.

I don't know if the bass bar gap changes these patterns but I'm guessing that the resultant sound either gets better or worse or stays the same for various people.

 

1. "Visualizing Instrument Vibrations and Sound Fields-The State of the Art", Nils-Erik Molin, CASJ Vol. 4, No. 5, May 2002, fig. 3 page 23

 

2000Hz Holograph.jpg

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Christian congratulations on your many fine instruments, they sound very good! Also kudos for getting in the Strad! I commend you for having the courage to do something different, which in this realm is an achievement within itself.

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That is really brilliant!

To me it resembles a spring that would change the dynamic of the bow,,,,, starts might be faster and crunchier, with more grip.

The low end, sprinkled with a bit more highlights, stardust,,,,,moon dust,,,and sparkles,,more mid range to the high strings,,they might feel stronger.

My thoughts to nite,,,

Italian pizza's ready.

Evan Dreamer

 

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