Thin Tops Better?

*Thin TOPS not thin bodies

I posted a similar question in the uke builder's thread but I'm curious to know what players think too. I don't know if this is correct, but somewhere a while back I read that the thickness of the top is the single most contributing factor to a ukulele's volume/projection. Is this true. For some reason, that always stuck with me and I've always wondered why uke makers don't offer a line of ultra thin-top ukes. I'm sure they'd be more prone to breaking, but I'm also sure a lot of players would accept that risk for the sake of louder (improved?) sound. I might be way off base here, but it's just something I've always wondered about and figured I'd quit wondering and just ask the community.

They exist: they’re called banjo ukes.

You don’t need to go thin to create volume: you can also increase volume with a resonator.

Volume isn’t the only thing affected by a thinner top. It changes the quality of the sound. A skilled luthier balances strength and stiffness to achieve their goal sound. There is no absolute best here. It’s a choice of trade offs.

I think the instrument's tone, sustain and dynamic range are mainly controlled by details of the design and materials, not by a single factor like soundboard thickness. With that said, the loudest classical guitars I have played have really thick tops—i.e., double soundboards with carbon fiber honey cone bracing between the two soundboards. I haven't played any double top ukuleles but my loudest ukulele, a Kremona Coco, is a real screamer has a fairly thick spruce top with all sorts of bracing inside.

Better quality ukuleles usually do use thinner soundboards. I think the main reason that cheaper ukuleles do not is that thinner soundboards require more time and skill to work with, which would increase the costs.

I think the sound boards on some high-quality ukes have soundboards of varying thickness. Thinner in the middle and thicker at the sides.

It has to do with the sound of the wood. The strength. The bracing. The build. Some do extensive tone tapping to shape the wood so it resonates as desired.

Not all are made this way.

Thickness of top back and sides, quality, shape and thickness of bracing and the balance of it all is the primary reason one pays top dollars for a uke.. since a luthier can adjust every bit based on what they hear is the reason why machines don’t make the best ukes.
My first ukulele was a Makala Dolphin and eventually I ran some experiments.
1. Fixed setup
2. removed all paint from top, back and sides. The back is some plastic/hard board kind of material and not the same a fluke
3. sanded the top down to the point the wood not barely glued to the sides at some spots (that was a mistake)
4. Sanded down a ton of material off the bridge.

The uke looks like a disaster but sounds amazing!! Warm, highly resonant, long sustain.

So, the science goes like this: you pluck a string, its energy vibrates the top (soundboard). Thicker the soundboard, less the vibration amplitude (more mass to move) and slower response (must over come inertia). A thinner soundboard is better because it is more responsive and less wasted energy. But a thin soundboard is also weaker, so it must be braced more heavily (adding mass). It's a balancing act between soundboard thickness, bracing, and design (e.g. a domed/arched structure is stronger than a thicker flat structure, so a soundboard can be arched).

Top thickness is just 1 factor out of many that influence an ukulele's sound.

But as a very general rule, thinner tops tend to be louder and more resonant sounding.
This depends on a lot of other factors though, like the design, type of wood, bracing and the craftsman.

I've always wondered why uke makers don't offer a line of ultra thin-top ukes

Click to expand...

They do.
They're not usually marketed as "ultra thin top" ukuleles per se, but as an example this Kiwaya solid mahogany soprano is ultrathin as per this part of the review:
https://youtu.be/BN1DgGqgA_A?t=74

Basically, yes, for all the reasons stated above (physics: thin tops tend to react more to any string vibration).

And the nuances above are also correct: thin tops mainly result in greater volume, not necessarily greater tone; design (mainly the bracing system, the 'rib cage' supporting the top) also contributes a lot; as does the choice of woods.

Two things I can add to this interesting discussion:
1. a trade-off for thinner tops, is that they are also more prone to damage: bellying, cracks, loose braces. That's why high volume ukulele factories shy away from too fragile tops. No matter how much better they can sound, the warranty policy dictates to calculate some extra margin.
2. it's a general rule of thumb that tops contribute more to the sound than backs and sides (which should be stiff and light) in an 80/20 distribution, but that only applies to soft top/hard back string instruments, like most violins, classical guitars, steel string guitars, mandolins. Hardwood (koa, mahogany) ukuleles and floppy cedar flamenco guitars do require responsive (and thus light and thin) backs and sides.

You're getting a lot of great feedback here. The one thing I would add is this: There is danger in focusing too much on one specific variable. I think it's dangerous to say something like "X is the most important factor in determining Y." Yes, a thinner soundboard is likely to make an instrument that sounds louder and has a more pleasing tone. But if you're aware of, and controlling, other variables as well, it's trivial to build an instrument that appears to disprove that general rule.

The top doesn't really care how thick it is (within normal uke top thicknesses). The things that really matter are the stiffness, elasticity, and mass of the top (assuming all else is the same). Those are the physical properties that influence how it vibrates (and how the vibrations decay). Thinning the top plate itself is one of many ways you can influence those three parameters. But it's not the only way, and it's probably not even the most practical way. You can change the stiffness and elastic properties by changing:

- the wood choice for the soundboard
- the bracing pattern, how the braces are carved, what wood is chosen for the braces
- size shape and species of the bridge
- size shape and species of the bridge plate
- size and position of the soundhole
- material and size for the rosette
- size, shape, and species of linings
- the type of finish
- the dish radius
- the overall shape of the body
- the size of fretboard overhang, the thickness of the fretboard, and the species of wood used for the fretboard
- the size of the tail block and neck block

And that's just the top! Not to mention the back, sides, and neck.

Ultimately, there are practical considerations as well. Generally you can make a top perform better by thinning it, but there comes a point where things go badly very quick. If the overall top structure (including the braces) is not stiff enough, it will belly under string tension. If the braces versus the top stiffness aren't well matched, the top can crown around the braces (so the bracing telegraphs through the top and the top looks wavy). Even if you manage to solve for those problems, there reaches a point at which the top may be structurally sound, but becomes so thin it can no longer pump air well (at least, within the confines of a uke body). A top that is progressively thinned will reach a point at which the tone and sustain just sort of die - it stops sounding like a fine instrument and starts to sound like the top is made from cardboard or paper or something.

And as I mentioned above, it's possible to alter other variables to get to the same goal as a thin top. This is essentially what happens to combat "I can't make my top thinner or I'll have problems." You adjust all the variables in relation to each other to account for limitations. Bracing can be altered to accommodate a top that "wants" to be a certain thickness, for instance. And so on. Building an acoustic instrument is about balance, compromise, and understanding interactions. There is never really a single "best" value for any variable, out of context of the entire design.

So, ultimately, at the end of the day, I don't think it's super appropriate to make a statement like "thin tops are better" because you really need to consider the entire package, not just the one variable. What you can safely say are things like, "thin tops are less stiff" or "thin tops have less mass."