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What Impact Would 1/2" Sides On An Acoustic Have?


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Not sure what is referred to by the "monopole" in this case. However, if referring to the 0th-order mode of the top's vibration, then I agree. However, if you still use kerfing, you also risk increasing the natural frequency of that mode due to the reduced surface area. If you don't use kerfing, you might get approximately the same natural mode, but your directivity pattern of sound radiation will differ as well.

Other possible outcomes that could happen:

- a slightly less complex harmonic spectrum, since you are restricting more surface are to be more rigid (and thus more closely approximate an ideal Helmholtz resonator)

- some unforseeable consequence due to changing how the front and back are coupled (could be good or bad, no way to tell without doing it)

- a possible change in sustain due to increased mass and top stiffness

- a heavy beast as mentioned by WezV

Of course, when it all comes down to it, it all depends on what you want. We can discuss what the change would do from a physics standpoint, but an experiment is the only way to really konw for sure what the sound and your perception of it will do. Let us know if you go through with it, as I think it would be fun and interesting to hear about (and hear).

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Ripthorn: monopole is the same as the 0,0 vibration mode, yes.

Daniel Friederich uses thicker sides than usual (4-5mm) literally all the time. So does the Ramirez 1a, the absolute standard by which concert classicals are judged, and having played a few of them I can tell you that they are very powerful instruments. Many Australian lattice-style classical builders also use big beefy sides - in fact, some are so heavily reinforced that they are barely recognisable as guitars from their interiors: http://www.schrammguitars.com/lattice.html . Gregory Byers uses 6mm thick laminated oak kerfings (unkerfed, that is) for their increased stiffness, not to mention solid maple harmonic bars on his soundboards... I wouldn't describe any of these instruments as sounding constricted or harmonically simple: rather, I would say they represent some of the loudest concert classicals one can acquire. It's not just classical guitar makers, either: Ervin Somogyi uses thick-ish laminated sides on most of his instruments as well (for a variety of reasons).

Some reasons why thicker sides are actually beneficial:

- Making the sides thicker doesn't mean you have to make them thicker inward (and decrease soundboard area) - you can just as easily make them thicker outward and just have a slightly larger guitar, so there need be no loss there.

- Yes: thicker sides are stiffer. Specifically, stiffness has a cubic relationship to thickness. Sides that are 2x as thick as usual are 8x stiffer already (2*2*2 = 8), and that's still a mere 3/16" thick. And frankly, stiffer sides aren't a bad thing. Rather...

- Stiffer sides mean less energy lost to the sides. In other words, more of the string energy delivered to the soundboard stays in the soundboard - it is less likely to be absorbed by the sides. This means that energy is used more efficiently. As an analogy, picture two speaker cabinets: one cabinet and its baffle board are made from inch-thick solid oak (...thick guitar sides...), and the other is made from cardboard (...thin guitar sides...). They both contain the same speaker (...soundboard...). Which cabinet is likely to be more efficient and have the better frequency response?

- The slightly increased gluing surface could have a slight effect on soundboard stiffness, I suppose. However, I would say that this is yet another blessing in disguise: extra stiffness with NO increase in soundboard weight? Awesome. The soundboard could then be sanded thinner around the periphery to obtain the usual lower (aka proper) stiffness and the low monopole you're looking for, resulting in the desired proper stiffness while also eliminating a bit of weight. This is a good thing. Any way that you can make a soundboard lighter without compromising its proper stiffness is going to result in a soundboard that makes more efficient use of the strings' energy.

- RE affecting the back/soundboard coupling: All the research I've seen suggests that soundboard-to-back coupling is largely achieved by sympathetic resonance with the vibrating air inside the instrument rather than by some sort of transmission directly through the sides. This goes for all the string instruments, AFAIK. Side stiffness thus shouldn't affect this aspect of sound production. However! It would have the same effect (if any) on the vibration of the back as it would on the front, and if you're concerned with the tuning of your instrument's back (as many luthiers are), then you need to pay attention to what is going on there too.

- Something people haven't mentioned yet: stiffer sides = a stronger & stiffer platform to attach your neck to, which means 1) less energy lost at the neck joint, and 2) better resistance against the eventual need for a neck reset, because the stiffer sides can help combat an unwanted change in neck angle. It's a lot harder to twist thick sides than it is to twist them when they're 0.08" thick. Trust me, I've tried.

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All in all, I think that any effect the thicker sides will have on the tone production of the instrument will only be a small part of the big picture of the instrument, but the effect will be beneficial IF properly accounted for rather than just used blindly.

As for the weight: the sides of a rosewood guitar weigh about 0.6 lbs. Doubling the thickness or even tripling it will only result in a small increase in weight - the instrument will still be light compared to something like a Les Paul. If you use something stiff and light for your interior laminates (for example, Ramirez uses Cypress), it's an even slighter increase yet.

Edited by B. Aaron
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Can't say with a guitar but I play upright bass. In the late 19th and early 20th century there were a lot of basses made in France with thick sides. There is a fairly even stream of work for luthiers thinning the sides. Reportedly it makes a big difference. Also I would think bending thick sides would be a real pita.

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Yeah, bending thick sides sucks. That's why sides were made thin for hundreds of years leading to the traditions we have today, and that's also why anyone who makes thick sides laminates them from several pieces of wood. For example, Friederich uses two 2mm layers of EIR laminated together to produce simple double-thickness sides.

Coupling: Oops, I forgot about sound posts in the bowed instrument family. The front-to-back coupling is rather different there, isn't it? They don't really need to rely on the resonance of the air cavity... But again, the instrument relies on the soundpost for coupling rather than the sides. In fact, even luthiers of the viol family are aware of the importance of side stiffness. To quote from "The Art of Violin Making" (Courtnall & Johnson, 1999) regarding this very matter:

"...[the linings] offer an elegant solution to the problems of using thin, lightweight ribs. The joint between the rib and the front (or back) is under stress when the instrument is being played. As the plate vibrates, the joint is flexed in a small rocking motion, which needs to be contained. By almost tripling the gluing surface at this point, the problem is overcome... In addition, there is also a laminating effect when the linings are glued to the ribs, fixing the outline shape rigidly and strengthening the ribs."

As for thinning the sides of French double basses, I can't really comment about it because I've never personally heard of that procedure. However, I can quote somebody else about the sides of French basses: "French upright basses tend to be very focused and project better. It's a characteristic that comes from the maple sides and back. There is more power with maple because the wood itself is stronger and not as soft as poplar or walnut." I would say that this again supports the stiffer sides = more efficient argument.

Luthiers will do funny things to instruments for cash, especially when the customer is inclined to listen with their wallet rather than with their ears.

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