The Thin Ukulele: An Experiment

I spent over an hour with my master guitar luthier friend talking about sides and the depth of the box. His verdict? The height of the sides makes very little difference in how the top responds and the sound of the instrument until you get to the extreme ends of very, very thin or very, very deep. He has done extensive experiments on this. He did this by using binding tape to tape a back on a guitar with a top glued on and running it through the band saw to get a thinner and thinner body after each test. The testing was quantitative rather than qualitative using acoustic measuring equipment. In a nutshell (and this was a long, long conversation so I will summarize) this is what he found: Much to his surprise, it made almost no difference how the instruments sounds (responds).

So just for the fun of it, I'm going to make a thin ukulele and see how it sounds. I don't have any fancy sound measuring instruments so it will be qualitative (how does the thing sound?) rather than quantitative. I basically pulled a number out of the air as half the depth of my usual ukes sides which worked out to 1 and 5/16th at the waist (not counting back and top thickness). The usual straight taper of 3/16th was reduced to 1/8 inch.

Nothing like actually doing something rather than thinking about it to immediately reveal problems (challenges?). First off the neck to body joint area is greatly reduced thus bringing in structural integrity issues. Maybe the size of the standard box is dictated not by what it sounds like, but by issues of neck to body structural issues? And second, it becomes immediately obvious that the sides are integral to how the box is strengthened overall by the height of the sides.

Just to be on the safe side (and my friend says no worries it will sound just fine meaning it will sound like a toy guitar ha ha ha), I'm going to put in an LR Baggs under saddle transducer. This is a side project so will report back by reviving the thread later which could be awhile. Picture below of the neck and tail blocks in. Pretty thin...

I have a Cordoba FCWE (2.5" depth at tail flamenco guitar) that I like. But it definitely sounds different than a normal depth box. The air resonance is much higher, so it doesn't have that "bung" sound on the low strings that most factory nylons do. More of a "tang" or "boing" sound. But it also has a fairly thick top and thick finish, and I've become spoiled on the much livelier guitars that I build, so I don't play it much anymore. Therefore, I have been wanting to build my own thin flamenco for a long time. And try a thin steel string too. Probably jumbo size. Seems like it would sound pretty interesting to have a very large and low frequency soundboard, but without a large air volume behind it.

What size uke is that? Tenor? That's what I'd do for this experiment.

Neck stability is indeed an issue. The Cordoba is getting toward needing a reset after 10 years.

Looking forward to hearing how it turns out

Yes tenor. 17 inch scale length.

The sound is going to be very punching, super quick attack and fast decay (i think)

I have been down this road for quite awhile now. If you really want to know for yourself you must make two ukes exactly the same way, same wood ...everything the same. One standard size and one thin one. I have done this more than once... Everyone prefers the thinner one. Your 1 5/16th sides is at the very bottom end I think.
Even if they sound and act the same the thinner uke is much more comfortable to play. IMO...
I have a 1 7/8 inch that I have played for 6 years almost daily. I have never had a neck to body issue, it's an uke... not much string tension to worry about..

My thinnest Uke is my National Reso-Phonic Maple Resonator, which is 2 3/16", including the thickness of the top and back. It always feels and looks very skinny to me. But when I play it, the tone and volume just jump right out at me. You might say that resonators are different than standard acoustic instruments. But still, a lot of the tone and volume have to do with the body of the instrument rather than just the resonator cone. Otherwise, they'd all sound a lot more similar.

OK. Interesting results he obtained.

Given you mention he is a guitar builder, as opposed to strictly ukulele, were these tests carried out on a full size instrument? I'm trying to understand what his scope of 'extreme ends' actually is. For example, on a medium steel string body, if his sides are usually 4 3/4", what were his outliers before notable change was present according to his data? As extreme as 2" on the thin to 7" on the deep? Or are we only talking 4 1/4" on the thin to 5 1/4" on the deep? I'm curious, as if I were to take your summarised comment on face value, that is "...height of the sides makes very little difference...sound...", I honestly can't quite understand that.

Changing the depth of the instrument will change the air volume of the body, which will change the helmholtz resonance, which will affect the performance of the guitar. The helmholtz largely determines the low frequency response of a guitar. Of course the hows, whys and effects of this are complex as the instrument acts as a whole.

Please don't take this wrong - I'm not being arrogant and I am not demeaning you nor your tutors tests or results, I am just trying to understand. It is all the more confusing as you suggest his results were gathered quantitatively, not qualitatively. I'd love to see his data.

In any case at the very least, I'm sure your experiment will prove interesting for you just the same.

Cheers.

J.F. Custom said:

Changing the depth of the instrument will change the air volume of the body, which will change the helmholtz resonance, which will affect the performance of the guitar. The helmholtz largely determines the low frequency response of a guitar. Of course the hows, whys and effects of this are complex as the instrument acts as a whole.

Click to expand...

Yes we talked about the helmholtz resonance (a phrase that meant nothing to me until he said that it was like blowing over the top of a jug. I get that). As the volume of air in the box decreases, the pitch goes up. You can literally blow air over the sound hole and hear the pitch. How this effects the ultimate sound of the instrument is unclear to me. You say that the helmholtz determines the low frequency response which I did not know. Since the guitar is a string instrument and not a wind instrument I assumed it had no effect. I will have to take your word for it because I don't know...

Anyway, thank you for your thoughtful comments and no I didn't take them wrong. It is called a discussion and not an argument. What bothers me is when people get personal with ad hominem attacks. (ad hominem, is an attack on an argument made by attacking the character, motive, or other attribute of the person making the argument, rather than attacking the argument directly.) This is what trolls do. I am not going to give the name of my informant here because I don't want him to get spammed by trolls/idiots. Some people can get all wound up about this stuff because they feel their personal beliefs are being attacked and they can get very nasty. The man is a respected luthier of some prominence and if you would like you can send me a PM and we can talk about it.

From my understanding the depth does not change the hole resonance much in a guitar as the top and back are not rigid as a speaker enclosure (or bottle) is. No idea about a uke.

Some unsolicited and highly subjective anecdotal evidence:

I have (and love) a thin-bodied Bruko soprano. It's sides are 1 1/4" thick. It's made entirely of maple.

Yes, I find it more comfortable to hold. No, it does not have great sustain (but this strikes me as characteristic of all Brukos I've owned/played). And strangest of all, it's the only soprano I've owned that can play tuned to B without muddiness on the low end.

Interesting project — I look forward to the results.

printer2 said:

From my understanding the depth does not change the hole resonance much in a guitar as the top and back are not rigid as a speaker enclosure (or bottle) is. No idea about a uke.

Click to expand...

Just one factor that will effect it, as is aperture size - in this case the soundhole size, as will a tornavoz. Complex systems guitars

Jeremy.