Vibrational Stiffness

[Giuliano Nicoletti]

Hi Paul,

Of course you can adapt the value of vibrational stiffness to your building style, or different types of sides. Generally speaking, it is mostly the density that’s affecting the decoupling of soundboard from sides; stiffness of sides is just shifting frequencies (of sides resonances), but not changing the boundary conditions of the soundboard. Keeping in mind that most probably the laminated sides are denser and heavier than traditional ones. That said, I suggest to try to measure these values and avoid comparing situations that are too different (classical and selmer styles guitars) without having solid references; it might be misleading. I hope this might be of any help.

Cheers,

Giuliano

[Paul M]

thank you @giulianonicoletti ! I’ll chew on that for a while. Much appreciated.

[William Reynolds Anthropocene Strung Instruments]

I’m running structured sides for all my builds. Though I’m debating doing a typical side build for other reasons soon regarding my neck joint at cutaway.

The way I understand the structured sides is that the vibrations in sound board are more likely to stay in sound board like waves in a concrete swimming pool do vs an above ground vinyl pool has the sides moving when the waves hit the sides. And this the waves in the pool dissipate faster, so less sustain.

Another benefit described in Trevor Gores book is the extra mass of structured sides help move the anti-node closer to perimeter of soundboard and increase the active area of the middle. More tone, more sound(I’m not going to explain this as well as I understand it).

A snare drum wouldn’t sound good with .09” sides,, and I believe a guitar is quite the same mechanism. So I’m just running them since I saw Jeremy Clark doing it at 52 instrument co.

As far as the sides allowing for the top to be thinner I wouldn’t put much more thought into that coalition. The bracing would make up for the difference in thicknesses. From what I learned studying Gore is the intention of all this math is consistent sounding guitars of exceptional harmonic value, so if you built the exact same guitar again with correct target thickness the sound would be more different than the difference of how two or ten guitars built exactly the same with same math rendering different top thicknesses though producing same sound. I hope I don’t sound like a complete dimbass, haha, and I’m not checking typos on this novel I wrote, so I apologize now for grammatical mistakes or spelling.

[Paul M]

My understanding of the top thickness thing came from building two instruments, side by side. One had traditional ribs and a thicker top, one had the structured sides and a thinner top. The structured side instrument had a huge non traditional sound hole. The trad sides one had a regular D hole.

They both sounded really quite excellent but the structured side instrument projected insanely well and had a really peculiarly room filling sound. I can’t say I’ve heard a guitar that filled a room before like this one.

And I did notice some deflection on the bridge of the trad one. My thought is that there is probably some pressure that the top puts on the side with a tendency to splay them out (notably: this is a guitar with a floating bridge and a tailpiece so the pressure is exerted downwards, not like a pin bridge kinda guitar). So perhaps this is a special case but my thought is that with the structured sides, there isn’t the opportunity for the sides to splay out. There isn’t noticeable deflection in the structured sides instrument.

But my knowledge of all this stuff is super limited. I do know that that guitar kicks serious ass. I hope that I can make another one as good.

[Paul M]

In rereading your post I see a lot of similarities of thought.

I don’t have the math or physics to understand the measuring stuff at this point, but my physical understanding of that guitar from watching it is that the top is really compliant (in my mind, this means it moves a lot), to the extent that it really puts out a palpable amount of air when it’s played. I do think about the drum head analogy a lot. The more I think about it, the more I’m wondering why I would ever not use the cored sides. The only possible alternative to me would be some sort of thinner composite side (carbon fiber or flax fabric) that had comparable stiffness at a lower weight. But I don’t have a real understanding of how that would effect the sound, just that it would potentially make a lighter set of sides.

I have been wondering then about the back too and how that could/should be compliant as well. I wrote to Jeremy asking about that. As usual in talking about this my understanding is so rudimentary that I have to ponder his reply for a while. But he is using a braceless back, which is pretty interesting to me.

I think Jeremy differentiates between ‘push’ guitars (archtops, selmer style guitars, other guitars with a tailpiece) and ‘pull guitars’ (Martins, gibsons, guitars with pin bridges). Or something to that effect. It makes sense that they would have very different issues from each other, I think.

Without the math to describe things, I’m left to analogies…how is a guitar like a speaker cone? Is that a helpful way to think of things? Or like an amp cab? Perhaps a better analogy.

Anyway, thank you for your thoughts. I am starting to measure stuff for some classical guitars, I assume this will be a long process trying to understand things.

[William Reynolds Anthropocene Strung Instruments]

I’d say since they both sound great you’re set. The room filling voice could be so many factors, but structured sides really do push the guitar like a hotrod. I’d recommend not comparing the two as on is a peach and other an apple, which are both great tasting. Build another of each the same way you did top etc but swap the sides to experiment and then you’ll be able to compare structured vs traditional on same design. But I will include the fact that the math Gore teaches and Giuliano has in their books is so you can build tops with different pieces of wood and expect similar results so when this is applied to two guitars,, one with structured sides and one with traditional built identical besides the sides,, then the comparison can be reliable determining just how much structured sides enhance the projection and voice.

Post some pics, I’m interested in your design.

[Anthony Kreher Kreher Guitars]

I think William was getting at a good point. The calculation of top thickness can help you get similar sounding results with different pieces of tonewood (relating to sound results from a top or back, structured sides, bracing and such will all be different factors)

If you like the sound of the structured side floppy top then maybe that’s a direction to go in. You can change the vibrational stiffness value in the spreadsheet to get a result you are looking for and then continually hit that target.

However, there is an optimal balance for a piece of wood. Too thick and it has too much additional mass. Two thin and it loses stiffness.

The optimal balance for a selmer guitar is absolutely different than a fingerstyle guitar. You will want it to punch but have quick note decay. Which is Probly why the flop top is so appealing.

[Paul M]

to be a bit blasphemous, I don’t really love a lot of the Selmer style guitars. It’s a bit of an odd situation because unlike Martin flat tops, Selmer hasn’t made guitars for 80ish years and I’ve never played an original. So it’s hard to say what the original sound really was. I have played a couple really nice French guitars from the same period. They are usually very bright with zero sustain, which is sort of the traditional sound but I don’t super love them.

What I liked about that guitar is that it’s a bit more midrangy, has amazing sustain and is just effortlessly loud. But it’s easy enough to make it bark for the rhythm sound.

Unfortunately I did no measuring on that guitar so not sure I can duplicate the stiffness of the original top. My friend is buying it though, he’s in town so I can get it back to measure a bit.

I just realized too that I didn’t take many pictures of the guitar. The construction was a little rough as I was just trying to see if it was going to work, so….no closeups. But you can see the soundhole in these pictures:
https://photos.app.goo.gl/6uehafhrdWAfsuRPA

There’s a bunch of videos of French dudes playing these guitars there….this is one of them side by side. Not sure the difference in sound really comes through on the recording.
https://photos.app.goo.gl/CTmGK6EZZnEQT1iX7

photos.app.goo.gl

2023 Gypsy Guitars

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[Anthony Kreher Kreher Guitars]

I have never played a selmer either or any guitar of that style honestly. But you know what a player needs out of a guitar like that. Make a list of all the characteristics you would want out of a guitar to play that style music. And then figure out how to add them all!

That’s great your friend is buying it. You should def keep it close for measurements. Do as many experiments on it as possible. At the very least take a FRC of it so we can talke a Look too! Although that will lead to more questions from us and you having to do more testing.

[Paul M]

yeah I will do that. I need to do a tune up on it anyway.