Single Most Important Factor For Volume/Projection?

I'm not a uke builder, but I've always been curious about this element of the build process because somewhere I once read that the thinner the body's top, the louder the uke will be. For some reason that always stuck with me so whenever I'm shopping for a new uke, I always wonder "why didn't they make the top a little thinner? Looks like there's room to." If so, I'd rather have an ultra thin top and be forced to be super fragile with it, than one that's thicker but doesn't sound as good.

I know there's a host of contributing factors, but how important is the thickness of the top? If I were a builder, I'd consider separating myself from the pack by offering "utra-thin tops" and have buyers just accept the associated risks (prone to cracking?) for the sake of volume.

The problem with building a louder instrument is there's a plethora of factors that impacts every aspect of sound. It makes sense to think a thinner top would be louder, because the top should be able to vibrate more freely, and in some cases a thin top is louder. However I believe stiffness and weight to be more important, after all every piece of wood is different. Meaning top thickness, top weight, brace height, brace width, and brace weight all have a major affect on the sound quality and volume.

With how many variables there are its incredibly hard to make an instrument louder without sacrificing structural strength or sound quality in unforeseen/unintended ways.

And the problem with thin tops is its not sustainable for the instrument, although there is little string tension from ukulele strings, over the years the top will distort, eventually making it unplayable.

Instrument making is an incredibly fragile balance, and there's no way to know for sure how changing one variable will change and the others.

I just answered your related post in the Uke Talk forum. I don't think there is an answer to "Single Most Important Factor" for any specific trait (tone, volume, sustain, etc.) A uke is a system and the variables involved need to be taken in full context. You could talk about which variables more important, but I don't think it makes sense to really talk about MOST important. And you can talk about how a specific variable influences certain characteristics, but that needs to be considered in context of the entire design. If you were to try to quantify this somehow, it would be easy to max one variable in one direction but then effectively cancel it out by maxing "less important" variables in the other direction.

And of course all of these variables have soft limits in terms of what can practically be built. Keep thinning a top and it will become less structurally sound. But if, for some reason, you really wanted to go beyond the typical physical limitations for a top thickness, you could adjust other variables to give you a wider envelope in one direction or the other.

There's also a consideration on what "counts" as a uke. What set of parameters add up to an instrument that we would call a ukulele? If you want a louder instrument, make it bigger. A "ukulele" the size of a classical guitar would be much louder than a typical tenor ukulele! But it wouldn't really be a ukulele any more, would it? For a less obvious example, you could abandon a typical braced top design, and replace it with two very thin tonewood plates with a foam or honeycomb substrate between them, and make a thick double top with no braces. Does that count as a ukulele? If it does, you've just thrown the whole "top thickness" discussion out the window...

Also - I hope you can take this as well-intentioned commentary, but making a statement like "if I were a builder, I'd just build thin tops and have the customer accept the risk" makes it sound like you've never been in the position of putting your name on something and then handing it to a customer. There's already a huge level of risk and trust involved in building and selling a ukulele, even if you don't make it "more risky" by thinning the top way out. We could go down the rabbit hole of customer relationships and builder reputation once your instruments are out in the wild, but I don't think that's where you wanted the discussion to go so maybe we should just leave it at that.

Ultimately, buyers who want loud instruments and have a legitimate reason for wanting them loud are generally already able to work within the confines of a typical ukulele design (i.e. without needing a builder to build a risky instrument). If you're recording or playing in a group ensemble in public, there's going to be some element of amplification involved, so the loudness question is solved that way. I don't want to speak for other builders, but ultimately things like tone, style, and durability probably trump the ultimate pursuit of volume-at-all-costs when making decisions about instrument design.

Or, for people who just really, really want an acousticly-loud ukulele, the other involved variables can just be maxed out, without putting risk into an ultra thin top. For instance - make the body volume larger, which will not just increase volume but will shift the resonant frequency lower (which, for a uke-sized instrument, gives the perception of more loudness most of the time). This can be done subtly, by changing the curves on the bouts and/or the body depth, to give more volume but generally stay within the confines of a certain instrument shape. Or, add a sound port on the upper bout that faces the player's head, so they hear more of the sound, even if there isn't more sound generated. Also, focus tonewood selections on woods that have better stiffness to weight ratios, which will naturally produce more volume (the string's energy has less mass to displace, and the mass will be more efficient at pumping air). And so on, and so on. None of those things inherently carry the risk of a too-thin top, but all of them can add up to a noticeable change in the perceived volume.

So, ultimately, I hope I'm just reinforcing the point that the whole is greater than the sum of the parts. It can certainly be very fascinating to learn about design and what variables influence what (I think that's probably a major reason why most of the people in this subforum started building). But it's important to not get too hung up on extrapolating bits and pieces of knowledge to the process of buying or building or marketing a ukulele. Simply put, if you want a louder ukulele, just look for a louder ukulele. Don't get hung up on looking for one with a really thin top, expecting that to be the way you get your loudness. Or - if you are going to get a builder to make you a ukulele, don't ask for a thin top. Instead, ask for a loud ukulele, and then have a discussion based on what the builder tells you he is able to do (or not do).

Loudest uke.

Which reminds me. Thin soundboard, thick sides, very thick back. That should move things more towards the Smallman concept. Of course one could go all the way and build a stripped down lattice with carbon fibre. Then couple it with immovable sides and multi-laminated back. It would end up rather heavy (Smallman's are hugely heavy). You should gain volume. The whole idea of the construction is to keep the string energy in the top, maximium efficiency.
Whether you like the resulting sound is another matter. Many think you gain volume but at the expense of a sound that they dislike. I have heard the odd Smallman that sounds very impressive but I've also heard some that I could barely listen to.
I guess someone somewhere must be making a uke version?? Other than that, yes the banjo version.

https://youtu.be/DdXEzIo6IDc

This is a great video to watch about how to get more volume. Trevor Gore talking to Robbie O'Brien about the science behind it all. They are talking about guitars but the science is the same. Very interesting things e.g. stiffness of the sides makes no difference, per se it is weight around the perimeter of the soundboard that increases volume. I found it fascinating.

There isn't one... it's a combination of things often unique to every builder.

The top thickness and stiffness are just two factors. Other important factors are type and weight of bracing, volume of the uke (top surface times height of sides), and an arched vs flat back.

merlin666 said:

The top thickness and stiffness are just two factors. Other important factors are type and weight of bracing, volume of the uke (top surface times height of sides), and an arched vs flat back.

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Others may know something I don't but I'm not sure the shape of the back (arched Vs flat) is actually as important as the rigidity. Arched backs tend to be heavier and stiffer and it is this the reflects the sound I believe rather than the profile. If you make a flat back equally rigid it will sound the same in my opinion. Certainly I have never seen any evidence to the contrary.

Red Cliff said:

Others may know something I don't but I'm not sure the shape of the back (arched Vs flat) is actually as important as the rigidity. Arched backs tend to be heavier and stiffer and it is this the reflects the sound I believe rather than the profile. If you make a flat back equally rigid it will sound the same in my opinion. Certainly I have never seen any evidence to the contrary.

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If you look at other instruments such as guitars or mandolins it is noticeable that those with arched backs or even bowl shaped bodies have much higher volume and projection than their flat backed cousins. The size, shape, and position of soundhole(s) may also be related to that. There's is probably some scientific literature on this available.

I'd have a hard time believing that the level of radius typically put on a uke back has any impact on volume (assuming all else remained the same). For me, our slight radii on top and back plates is more about resilience than volume or tone. If a totally flat plate tries to expand/contract with humidity changes, it has nowhere to go and is likely to crack. A small radius gives a sort of spring factor - if the top needs to grow or shrink because of humidity changes, it can push/pull into a tighter or wider radius easily without cracking.

I taper my ukes (3/16th of an inch or 5 mm over 1 foot or 30 cm) and compound radius the back (14 foot - 4.2 meters at the lower bout). Frankly I have never really come across any data other than anecdotal that this increases volume or projection, but I do it anyway and my ukes sound good. I do it because other instrument makers do it and have for hundreds of years which is not really a good reason but there you have it. I figure they must be on to something so I do it. Hey it couldn't hurt. There are other things in building acoustic instruments that also might not bear up under scrutiny. Tradition plays a big role.

merlin666 said:

If you look at other instruments such as guitars or mandolins it is noticeable that those with arched backs or even bowl shaped bodies have much higher volume and projection than their flat backed cousins. The size, shape, and position of soundhole(s) may also be related to that. There's is probably some scientific literature on this available.

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I think that is the point I am making. All else being equal they don't, people think they do and as Sequoia says many of us (me included) build with an arched back because tradition says we should. But so far there is no evidence it does. People expect it to sound louder so that is what they hear. And there is a history that says cheaper instruments have flat tops and backs and expensive ones have arched. But that doesn't mean it is so.

In the.end as others have said it can't hurt and has other benefits such as resistance to splitting in humidity fluctuations. But the volume thing appears to be so far unproven, in a scientific sense.

Michael N. said:

Thin soundboard, thick sides, very thick back. That should move things more towards the Smallman concept. Of course one could go all the way and build a stripped down lattice with carbon fibre. Then couple it with immovable sides and multi-laminated back. It would end up rather heavy (Smallman's are hugely heavy). You should gain volume. The whole idea of the construction is to keep the string energy in the top, maximium efficiency.
Whether you like the resulting sound is another matter. Many think you gain volume but at the expense of a sound that they dislike. I have heard the odd Smallman that sounds very impressive but I've also heard some that I could barely listen to.
I guess someone somewhere must be making a uke version?? Other than that, yes the banjo version.

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Yes indeed to all this.
Stiff sides (with mass and proper density) are major contributors. A reflective back (ie a stiff back) is an easy and sure way to further promote it.

A responsive top and good construction in general too but you should have that in any instrument.

The the exact opposite to a flamenco guitar, which needs to be built wobbly to dissipate that top energy down the thin sides and into a thin back.

The arch of the back has one effect on the volume, it makes the back stiffer and less subject to vibrate. In the projection end you do not want to waste energy vibrating a back that is most likely up against the player. I hate the term, 'reflective back' as the wavelength of sound in the box is generally much larger than the distance between the top and back. There is no reflection, building stiff and heavy as with a speaker cabinet leaves the energy in the top and not wasted.

printer2 said:

The arch of the back has one effect on the volume, it makes the back stiffer and less subject to vibrate. In the projection end you do not want to waste energy vibrating a back that is most likely up against the player. I hate the term, 'reflective back' as the wavelength of sound in the box is generally much larger than the distance between the top and back. There is no reflection, building stiff and heavy as with a speaker cabinet leaves the energy in the top and not wasted.

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A flat or concave back fits nice and snug to the players tum, and deadens the volume...an arched back only makes contact to a small area in the centre to the players tum. So less deadening....just a thought

Timbuck said:

A flat or concave back fits nice and snug to the players tum, and deadens the volume...an arched back only makes contact to a small area in the centre to the players tum. So less deadening....just a thought

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That is if the back is made flexible. The whole point is not to. It can be flat or concave (better for humidity changes) and made fairly ridged. I lust took a junk plywood guitar and shaved the lumber-like back braces down by at least a third and shaped them. It changed the back from a non-resonant back to one that is. It added some depth bass response and is now pleasing enough to listen to.