View Full Version : Body Profile and Tone

08-11-2010, 10:43 AM
I'm in the midst of my second scratch build, and I've been thinking about how to get the tone I'm looking for. It seems to me that adjusting the profile of the body--varying the depth of the sound chamber at the heel, waist and tail--is one way to do so.

For the pros and experienced hobbyists: are there any rules of thumb regarding the relationship between tone and body profile? For example, would increasing the depth of the lower bout improve bass response?

Thanks in advance.


08-11-2010, 03:20 PM
Hi Michael, you're asking big questions here. Here's what I think; body shape and size relate more to loudness than tone, bigger = louder. I've never had any problem getting decent bass response (I'm guessing you're a guitarist) from my ukes on account of the 3rd C string (being close to the body resonance) tending to dominate naturally. I want the outside strings to be as loud and clear as I can get them which is about getting a thin top with bracing of the right stiffness. You can get a mellower tone with a more flexible top but I wouldn't aim for that. If this is build #2 make it as well as you can, see how it turns out, if it's good do more of the same. good luck Steve

08-11-2010, 09:52 PM
Michael, if you're talking about chamber resonance (helmholtz resonance), then yes making the body bigger will lower the tone of the chamber resonance. The soundhole size also plays a role in determining the basic chamber resonance, so making the soundhole smaller would, in theory, lower the tone to some degree (within the range of the resonance chamber).

But I think you'll find -- as Steve (ecosteel) already said -- that it's really about the thickness and bracing of the wood, particularly the soundboard but also the the other parts. A thinner soundboard will drive the bass and mid tones better too, not just the trebles.

Hope this helps - YMMV

08-12-2010, 07:47 AM
Hi Michael, that is a thoughtful question and deserves an equally thoughtful answer, but in my experience things are seldom that simple. Keep in mind that luthiers do not agree on such basic issues as how much do the sides and backs of flattop instruments contribute to sound production. The body depth and taper are only a couple of the myriad of variables that contribute to the overall sound of an instrument, as Erich and Steve have said. Increasing the body depth will lower the body resonance, which is a combination of the helmholz resonance and the vibrational qualities of the body assembly. Whether that results in a better sounding instrument, who knows? Moving the back further from the top could have the effect of decoupling them. Check out David Hurd's website and his book "Left-Brain Lutherie".


08-14-2010, 10:05 PM
Brad, I'm so glad you used whichever side of your brain makes magic and did the body on my pineapple exACTly the way you did!

08-15-2010, 08:39 AM
There are so many great body shapes. I would simply start out by adjusting the body and/or neck so that the bridge sits in the "sweet spot." This is one thing that a lot of builders seem to overlook. The bridge should be placed close to the center of the lower bout.
The other thing i would suggest, is to find a uke with the tone you like, and copy that. This may not be the answer your looking for, but it is sometimes the most effective approach. Luthiers can make all sorts of generalizations, but there are so many factors that go into tone, and it takes years of practice and experience to truly understand all the tonal relationships............so mimic a ukulele you like, take good notes, and make adjustments from there.

Jake Maclay
Hive Ukuleles

Moore Bettah Ukuleles
08-15-2010, 10:12 AM
I've said it before but it probably bears repeating; No matter what shape you build make sure you can find a case to fit it!

08-17-2010, 03:42 PM
Just found this, could be interesting http://www.mimf.com/archives/body_size.htm

08-17-2010, 05:07 PM
Thanks, everyone. A lot here to research and think about, which is part of the fun. Ultimately, it looks like I'll just have to build lots of instruments, making small experimental changes until I hear what I want to hear. My Kanilea K2 comes close to the tone I want, and I'll try to mimic its proportions in my next build. But I don't imagine that plans are available for their TRU bracing design, unless, of course, I take the uke apart, which I'm not gonna do.

08-17-2010, 05:15 PM
One great way to trace bracing is to put tracing paper on the face and use a pair of rare earth magnets, one inside the box and one on top of the tracing paper an move the magnets along the braces to trace their location. Another method is to use a light inside the box and trace the shadow of the braces. Be careful of this one as the light can get pretty hot and affect the finish.

These methods are easier in a guitar where you can actually get inside the sound hole. Never tried it with a uke.

08-18-2010, 01:55 AM
Make sure the sound hole is large enough to allow a large/bass sound wave to escape. Too small sound holes restrict the tone.

08-18-2010, 04:20 AM
Make sure the sound hole is large enough to allow a large/bass sound wave to escape. Too small sound holes restrict the tone.

Careful, this might be misinterpreted as meaning that a larger soundhole would bring out longer/lower sound waves - at least according to the helmholz calculations a larger soundhole would make the tone higher (within the range of the given resonance chamber).

But you are right that the soundhole needs to be large enough to allow the sound waves out. As I have pointed out in the past: Too small will tend to sound trapped and stifled - but too large will sound thin and wispy.

YMMV, Erich