Upper and lower bout relative sizes

[agabinet]

Hi, this is my first post in the forum. I am a relatively inexperienced builder, but I am interested in trying some ergonomic ideas. The large lower bout and small upper bout design has never quite suited the way I sit with an instrument. Is there any acoustic reason that the lower bout should not be the larger of the two, for example, or that the design could not be altered to accommodate my leg better?

thanks in advance

Ari

[Ned Milburn]

Modern guitar design coalesced with Antonio de Torres of Spain near 200 years ago. On the Spanish guitar, the bridge is central in the lower bout, and the lower bout's sound-board is isolated and becomes a vibrating diaphragm, somewhat analogous to the electronic speaker.

If the lower bout was made smaller, then you'd have a small-soundboard instrument with a large resonating chamber. This doesn't make much sense.

The steel string guitar design coalesced with Martin. Isolation of the lower bout does not exist as it does in the Spanish instrument, but the lower bout soundboard diaphragm principle holds true, too. If the upper bout were big, and the lower bout small, you'd be doing the same and making a smaller resonating diaphragm with a large resonance chamber. Doesn't make sense.

Then, ergonomically, I'm not sure the advantage of a larger upper bout than lower...

[runamuck]

Originally Posted by agabinet

Is there any acoustic reason that the lower bout should not be the larger of the two, for example, or that the design could not be altered to accommodate my leg better? Ari

Did you mean to ask the opposite of what you've asked above? The lower bout IS the larger of the two.

[dekutree64]

For the most part, I'd say no, it won't work. Or at least it probably won't sound good. But you could always whip up a quick and dirty prototype out of cheap materials and see what happens. I'd design it so the bridge is near the waist, and make the bridge as narrow as possible so there's some flexibility to either side of it, and both the upper and lower bouts are activated to some extent. Maybe use two curved braces similar to Trevor Gore's falcate pattern. Perhaps use flying buttress bracing for the beadblock, so the upper bout doesn't need to be stiff for structural purposes.

[agabinet]

Originally Posted by runamuck

Did you mean to ask the opposite of what you've asked above? The lower bout IS the larger of the two.

Yes. Thanks. I find it uncomfortable to sit with that lower bout resting on my right leg. It pushes my right arm up and isn't very stable for me.

As far as the location of the bridge and the size of the resonating part of the guitar go, in theory could you keep the area of the lower bout the same by making it longer but narrower? That would solve my ergonomic issue. Might Change the resonant frequency?

[Truckjohn]

What sort of guitar patterns do you play? For example - dreads are very uncomfortable in the classical sitting position. They just do a lot better standing.

A smaller guitar body and a more pronounced waist also help a lot in this regard. For example try playing a 0 or 00.

If you look at old Russian and french guitar patterns - many have both bouts about the same size. Russian guitars traditionally had a very pronounced waist - especially compared to Italian and Austrian guitars - which frequently had almost no waist.

Anyway - I see no reason you strictly couldn't build one. It would probably work out more or less Ok... It would probably look crazy though. Probably be pretty hard to resell when the time comes.

But I would start with a smaller guitar body with a more pronounced waist for better comfort in the sitting position.

[runamuck]

Originally Posted by agabinet

Yes. Thanks. I find it uncomfortable to sit with that lower bout resting on my right leg. It pushes my right arm up and isn't very stable for me.

As far as the location of the bridge and the size of the resonating part of the guitar go, in theory could you keep the area of the lower bout the same by making it longer but narrower? That would solve my ergonomic issue. Might Change the resonant frequency?

I would think that the tone of an instrument you describe would be altered simply because of the bridge location in reference to the narrowing but lengthening the lower bout. Wood flexes more across the grain then with it and by narrowing and lengthening it the proportion changes from a traditional design.

But I've never read anything that would answer your questions with authority.

[Alan Carruth]

There some way of getting around the problem that don't involve such a drastic redesign. Consider, for example a wedge body, such as was patented by Smith and made popular by Manzer. Side bevels, which seem to have originated in acoustic guitars with Laskin, although Fender used them on the Strat, also help a lot.

Whenever you see a design feature, such as the 'normal' guitar shape, that has been the standard for a long time, you have to ask yourself why that is. In this case, there are acoustic reasons for it, although they're pretty complex. The bottom line is that if you want something that sounds like a guitar, that's what you have to build. The further you depart from that, the less like a guitar it's likely to sound.

[redir]

You might consider a leg pillow or a leg rest too.

[MC5C]

Rest the instrument on your left leg, like a classical player is my first thought.

[Glen DeRusha]

[QUOTE=

I find it uncomfortable to sit with that lower bout resting on my right leg. It pushes my right arm up and isn't very stable for me.

[/QUOTE]

Have the waist of the guitar resting on your right leg, not the lower bout. That should lower things a little bit and make it more stable.

For a more ergonomic thing you can, and it is all legal as far as I know,

Chop the waist in deeper, just on the passenger side. The side that rests on your leg.

Chop 1/2" off of the lower bout on the drivers side. The side that your arm reaches over the lower bout.

Wedge shape the body.

Put in a built in arm bevel.

Drop the scale length down to 23"

This was an OM size to start with.



Doesn't look bad when someone is playing it.



Or you could get an Ovation. They have these nice round backs on them. You can roll the thing and get the lower bout out of the way. Like a wedge shaped body, but better. You have more adjustment with the Ovation, to find the comfy spot.

Hope this helps.

Glen

[agabinet]

Thanks, I love that design. I think it's very aesthetically pleasing, actually, even if not symmetric.

I think I might build a slightly longer and leaner guitar just for the heck of it and see what it sounds like. My ear is not so discerning that I think I will HATE what comes out. I am not building for resale anyway . . .

As far as the acoustics of the design variations, I have seen so many guitars with so much variation in shape and they all still sound like guitars. My current build is asymmetric, a kidney bean shape with a waist at the bottom and single curve at the top.

Thanks for all the replies. All very helpful.

[Alan Carruth]

agabinet wrote:
"My current build is asymmetric, a kidney bean shape with a waist at the bottom and single curve at the top. "

Giannini in Brazil made those. There's nothing new under the sun.... The ones I worked on did not sound especially nice, but they were not very well made either.

[Truckjohn]

One tip on making asymmetrical and funny shaped things...

Make it asymmetrical enough and with features such that its obvious that it was intentional. That way it doesnt look like you simply messed up..

So - as was shown above... Pinch the waist on the down side more. Add a shoulder bevel and a wedge. Make it obvious that its supposed to be this shape and not a mistake.

Another option is to go slightly thinner on a standard pattern with a pronounced waist - so a 1/2" or 1" thinner body OM, 00, 0, or Size 1... A 3 1/2" or 3 3/4" deep Size 1 is fantastic for couch playing.

[Glen DeRusha]

[QUOTE= I am not building for resale anyway . . .

Thanks for all the replies. .[/QUOTE]

Are you using a radius dish? Or a dish that is shaped like a piece of a pipe? Or going free style?

This is probably the body shape that you are looking for.

https://youtu.be/JfGKfwl8opg

Glen