Can anyone recommend a good resource for "know" guitar tone dynamics?

[printer2]

Originally Posted by Davin

radius of waist curves

Came across this one somewhere but don't remember the answer. Compared a dred to a narrower waist, a sloped shoulder perhaps?

And just found what I vaguely remembered, need to thank Alan for this one also,

Originally Posted by Alan Carruth

Offsetting the soundhole has some interesting acoustic outcomes. One thing is that, for a given size of hole, the closer it is to the end of the box the lower the 'Helmholtz' resonance. This usually translates into a lower 'main air' pitch, and, on a small box, could very well enhance the low-end sound.

There are other internal air resonances that don't normally put out sound through a central soundhole, and those might become more pronounced in the output as you move the hole up. One would be the 'A-1' air mode; a sort of lengthwise sloshing of the air in the box. It's usually somewhere near the pitch of the open E string, but would be higher if you had a soundhole that could actually 'hear' it directly.

That 'A-1' mode actually does contribute to the sound of most guitars, but it does it by a circuitous route. What happens is that the 'long dipole' resonant mode of the top, where the bridge is rocking toward and away from the neck, tends to drive that air-sloshing mode. The top mode also often occurs at nearly the same frequency as the air mode, so that the two can work together particularly effectively.

If you've got them working together, AND the guitar has a reasonably pronounced waist, AND the soundhole is near the waist, the air mode actually appears at two different pitches, one of which can move air through the soundhole, and one that can't, owing to a different position of the 'null' ('node') of the air mode. All of these conditions seem to necessary for this to happen: Dreads, with no real waist to speak of, often don't show this, and moving the hole up into the upper bout also kills it. It doesn't work on a rigid tube, either, even with a waist and a soundhole in the 'right' place.

The variation of the A-1 mode that radiates often is up in the range of A on the high E string for a 'normal' guitar, and helps to fill in a hole in the spectrum where there is not another resonance that can put out sound effectively. Since this shows up on all sorts of guitars (except Dreads) with round holes, I tend to think it's something that's part of the design, even though nobody tried to make it happen explicitly. It's one of those things that 'fell out' once, and people liked it, so they kept the design elements that made it happen.

I did build one guitar with a pair of holes in the upper bout. We called it 'Caspar the Friendly Ghost', since, with the form my belly bridge takes, it did look like a happy face with round eyes. One thing that was notable on that guitar was that the 'crosswise sloshing' air resonance in the upper bout, which happened around 700 Hz on that one, tended to radiate a lot of sound toward the player, due to the interference of the sound from the two holes. Any note that had an overtone in that range came across to the player as loud, and you tended to back off on those. This was _not_ what the audience was hearing, though; to them those notes you backed off on sounded 'weak', because, of course, they were.

Acoustics sure can be funny sometimes...

http://www.acousticguitarforum.com/f...d.php?t=211110

[Davin]

Thanks for the AMAZING responses everyone, now I only have one question: Should I use hide glue or PVA to repair my skull now that Alan has properly blown my mind?
I will definitely check out the Gore/Gilet and Somogyi books, thanks for the recommendations. I have the Cumpiano/Natelson book now and it's really helpful but while it tells you "what" to do, it does not really go into a lot of detail as to "why". Example, I'm planning on starting with a semi-traditional classical and the book recommends how to peak and feather the fan bracing but it doesn't say why? Now I can certainly make assumptions from what I see regarding why the bracing arrangement, direction, mass, and sculpting was chosen but it would be nice to have some of these things explained so I didn't have to infer on everything.

[Alan Carruth]

Many of the older luthiers would reach for the hot hide glue, almost as a reflex. However, there is a (slight) possibility that you could get BSE ('mad cow') disease from hide glue, so it would probably be well to avoid it, especially for direct application to the brain. Of course, if a luthier got BSE, how would you know?

Since aliphatic resin would not dry properly in that application, I'd suggest CA, which was, after all, invented for surgery.

Where's the 'tongue in cheek' icon....?

[Davin]

Originally Posted by Alan Carruth

Many of the older luthiers would reach for the hot hide glue, almost as a reflex. However, there is a (slight) possibility that you could get BSE ('mad cow') disease from hide glue, so it would probably be well to avoid it, especially for direct application to the brain. Of course, if a luthier got BSE, how would you know?

Since aliphatic resin would not dry properly in that application, I'd suggest CA, which was, after all, invented for surgery.

Where's the 'tongue in cheek' icon....?

Haha haha, too funny!

[li2ljay]

Well I'm glad I'm not the only one with a cracked cranium ! I'm great full for the multitude of knowledge on this page , but I officially feel dumb as a brick . But I guess we all have to start packing in this info at some piont . So as a beginner I'll take there advise and use some CA to attach this to the frontal lobe . Great stuff guys !