Acoustic Guitar Construction

It makes sense to me that using an offset soundhole DOES take a weakness out of the vibrating part of the top, thus leaving more soundboard to vibrate.

So then it also seems to me that using the typical x-brace pattern, which is optimized for dealing with the soundhole in its normal position, might not be optimal for a soundboard with the offset hole.

Some builders use an A-frame type of bracing for this purpose, and that may work, but I wonder if there is not a better way to exploit the extra usable soundboard.

Any ideas?

The X-brace still seems like a good idea even with an offset sound hole. It is strong and nicely distributes its strength along the active parts of the sound board.

Seems the designers at McPherson agree with you Dave:


http://mcphersonguitars.com/technology/

Yeah they do, but then I don't see a huge stampede of builders going in that direction. :-)

It still puzzles me. If you take the soundhole out of its normal position, aren't you taking a weak area and replacing it with top? And removing the bracing that is there only because there was a weak area? So you have more top, less weakness, less weight.
I'm sure that is a simplified way of looking at it, but still, is the logic sound?
McPherson moves the hole towards the rim and perhaps he has good reason to do that, other than a marketing feature, but I would think that, since we take pains to make the top thinner at the rim and for good reasons, that he is removing a part of the top that contributes a lot toward responsiveness.
Just spitballin' here, of course; I'm going to email George Lowden and Mike Doolin and get their take.

edit: I did email Lowden, Doolin and Howard Klepper. I'll post what they send back.

I know from my reading about classical guitar and violin designs and construction the luthier needs to produce an instrument with a fairly defined sound. There are lots of ways of making more efficient instruments but when a builder strays to far the tone\characteristic sound of the instrument changes.

Violin sound boxes are built in the same shape from before Stradivarius's time. This is true even though they changed the scale length and they have tuned them to a different concert A. I am sure it would be easy (for one in the know) to make a more efficient and performant instrument. But the trick is it has to replicate a very narrowly defined sound.

There has been a lot of innovation in classical guitar bracing design because classical guitars are often used in performance halls without amplification. Loudness and efficiency are very important. Still the struggle is to produce a loud guitar that still sounds like a Taurus.

Kasha used physics to develop efficient brace design for a classical guitar, besides radically different brace design these guitar include offset sound holes. Despite a lot of effort this design never really took off. I think part of that is a lot of them did not quite sound like classical guitars to the refined ear. I did hear a Kasha designed guitar built by Richard Schneider and it sounded wonderful. Right after that I heard a different Kasha braced guitar played and although it sound OK but it did not sound right.

I guess where I am going with this is that builders start with the design that produces the sound they are looking for. From there the design can be tweaked to enhance the performance without changing the characteristic sound. Keep in mind the weaknesses in the guitar design my very well be contributing to the characteristic sound. I suppose every now and then a great performer can take a new sounding instrument and define a new sound. Williams\Smallman might be one example in the classical world, but it is still too early to tell.

Thanks for that thoughtful post, John, you made your points well.

Part of the discussion has to revolve around the concept of 'characteristic sound', as you mentioned. There would really be no need, other than a marketing angle, to move the soundhole and then try to duplicate the characteristic sound of the hole in the standard place. In other words if we like the sound of an instrument as normally built, why change it, unless to gain volume or some engineering advantage, etc?

A reason for innovative design is marketing. A musician crossing over from electric to acoustic, for example, might well be drawn to a very thin neck profile, a more focused sound as opposed to the wide, open sound of a vintage acoustic, and a more aggressive design with cutaways, offset soundholes, whatever. The instrument he chooses will not have the 'characteristic' sound that most of us really like, but it will sound good, be easy to play, probably have an ust. It may be a Takamine.

Another factor is that many buyers care more about shiny, eye-catching shape than anything else, as long as it is easy to play. Headstock bling and high-gloss shine and cutaway are the first things most buyers notice, according to many music store owners. Which makes me ask whether making a sale is more important to me than striving to replicate a certain sound.

So many guitars, so little time...:-)

A thoughtful response from Howard Klepper:

Dave, I've built a couple with offset or other than usual soundhole arrangements.

The first thing anyone should think about if they aren't going to have a conventional soundhole is how they plan to glue the bridge, and how they would fix loose braces and cracks down the road. These can be done, but I once asked this question of someone who was about to start building his radical design and it hadn't ever occurred to him. The soundhole is a construction and repair access.

The conventional hole is a weak area, but it is placed at a very strong place on the top--near the waist, where the top has the most support and the sides are stiffest. Any guitar is going to want to fold up there; resistance to that comes mainly from the sides. So we weaken the top with the hole, but make that up with bracing. I guess a top with an offset hole needs less bracing around there, but since the guitar wants to fold up there anyway, I wouldn't take much out.

The top weighs a whole lot more than its bracing. No central hole means more weight in that area, not less. Again, you won't get bracing down to zero; it's still needed.

Conventional hole takes away radiating area in a place that is fairly active in the first few modes. But it's not the center for those modes, and may help them by providing a flexible spot for the lower bout to hinge on.

Re your McPherson comment: Some people thin the top at the rim. Since the idea is to provide flex there rather than radiating area, I don't see how he is lowing responsiveness from that feature alone.

I think unconventional soundhole placements can be viable. But they aren't going to revolutionize the guitar.