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A discussion of why using the ring-and-a-half Chladni mode pattern, while shaping braces, will improve the sound (volume) of the guitar is attached. Although differential equations are used to show how the stiffness to mass ratio plays and important roll in establishing the necessary isotropic properties, no math skills are required. The use of the ring-and-a-half mode pattern is used to confirm the existence of isotropic properties.

Is there a question in there?

Jack - it sounds like you intended to attach a file but it didn't come through. I for one am very interested in the topic though.

Me as well!

Wood is orthotropic......

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http://www.PeakeGuitars.com

A braced top, in many ways, is closer to isotropic.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I uploaded the attachment but I don't know what happened to it. This web site showed it uploading. Any Suggestion of how to upload an attachment would be appreciated.

True, wood is anisotropic the equation for harmonic motion requires isotropic properties for efficient harmonic motion. We use and shape the braces to achieve this result using the ring-and-half mode pattern to let us know when we have succeeded.

Is it a word document? I don't think you can attach word docs here.

Can you save it as a PDF?

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Evan McCartney

Yes, it is a Word Doc. I will try to convert it to PDF.

If anyone wants to view the whole paper (6 pages with photos and math), send me a request in an email to: J2guitar@aol.com and I will email the paper to you in a return email.

PFD was not available and this site does not accept HTML.

Here is another try at a Word doc.

The extension doc is not allowed on this site. I'm stuck, send me an email at J2guitar@aol.com for a copy of the paper.

Here is a PDF copy of Jack's paper:

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thanks for posting the pdf Bob

Fred

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Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

A discussion of why using the ring-and-a-half Chladni mode pattern, while shaping braces, will improve the sound (volume) of the guitar is attached. Although differential equations are used to show how the stiffness to mass ratio plays and important roll in establishing the necessary isotropic properties, no math skills are required. The use of the ring-and-a-half mode pattern is used to confirm the existence of isotropic properties.

This is a repost with the PDF File attached.

I'm still waiting for someone to say, 'If you get such-and-so shape on your pattern, then take some off of the brace at thus-and-so point.' Guys seem to be saying, 'Experiment around with your bracing until you get a circle and a half.' Of course, I'm missing something. I wonder what.
Hugh

Hugh, if only it were that easy. It is hard to predict how shaving braces will affect the pattern.
For example, I was building a cutaway and braced it up before cutting out the excess plate for the cutaway. I was having a hard time closing the ring and decided to stop and go with it. I then cut off the cutaway portion and the ring closed beautifully. Go figure.

It is easier however to get good mode shapes with certain bracing patterns, i.e. symmetrical bracing patterns are much easier.

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Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

Hugh wrote:
"I'm still waiting for someone to say, 'If you get such-and-so shape on your pattern, then take some off of the brace at thus-and-so point.'"

If you guys would all build things in exactly the same way we might be able to do that. We could just specify a plan, and make everybody stick to it, and that should work.

Well, maybe, if we could specify wood properties like we can those of metal for machines.

And no cheating: when the plan says .120" then you'd better be at .120" or the Plate Tuning Police will be on your case! Best get your calipers calibrated, boy. Watch the humidity, too!

In short, there are too darn many variables involved. It's a _little_ easier with violins, where the structure is more standardized. Even there, changes in arch height and shape can alter the way things respond.

Over time, as we gain more experience with this, we'll start to find some guidelines that will help. One thing that will make this go a lot faster is if people will share their experiences.

RE: Where to start carving to get the ring mode.

The lines will move away from Stiffness and towards Mass. Carving below the bridge will close the bottom and open the sides. Carving above the bridge will close the sides and open the bottom.

See Introduction on posted paper "The Theory Behind Freeplate Tuning using the Chladni Mode Patterns"

Scroll to the post above.

Thanks, Jack. I knew I had to be missing something, there is just too much interest in this subject to be otherwise. I had read that intro and missed the critical sentence.

Take a look at the beam deflection equation towards the end of the paper to see how to manipulate the Stiffness to Mass ratio.

An up-to-date revised version of the paper "The Theory Behind Free Plate Tuning using Chladni Mode Patterns" can be found at www.JackJohnstonGuitarMaker.com under the "Lutherie Tab"

Also under the "Lutherie Tab" is a discussion of QE/D an indicator of performance of Guitar Plates. Q is an electronic signature in digital form of the tap tone, E is the modulus of elasticity along the grain and cross grain multiplied together, and D is the density expressed as specific gravity. Values within species can be compared to each other plate in the species.

Good ta see ya Chris