How does top thickness affect sound?

I am new to the Luthier's area, but have been lurking for some time. As a former carpenter, I excited about the prospects of building some ukes, just as soon as I can tool up. In the mean time, I am thrilled to have such a place to learn construction techniques from the pros.

Today, I have a question about sound board thickness. I have a Pono Ohai soprano, widely known by those in the know as a quiet instrument, assumed to be because of its overly thick sound board. Not satisfied with the easy answer, I thought I would dig deeper into what effects a think top have volume in general and perhaps more importantly, what it does to the volume and tone of each string?

As I play this uke, I find that the C string seems to resonate pretty well through the thick top, but the higher strings all but disappear, especially as I strum louder. Is this what one would expect? After reading a thread about SouthCoast strings, it got me thinking about the effects of string tension on soundboard vibration. Can thick soundboard issues be overcome by different strings? My gut feeling here is that they can, but not in the way most people would accept. In order to get the strings to balance, you would have to use looser low strings to reduce their volume to match the quiet high strings. Am I right here?

I also have had another idea I would like to pass by you luthier gurus. Another option I thought of to overcome the thick soundboard would be to make it thinner. I read one post were a guy sanded it down significantly and it made a substantial difference. Rather than going through the hassles of sanding and refinishing, I have been thinking about taking the uke to a laser engraver and give them a cool picture of waves crashing onto the beach or some intricate pattern and have them etch it into the sound board, effectively thinning it by say 25%. It could end up being pretty cool looking. Any thoughts?

Hi Mike, here are some of my thoughts on this. I would generally resist the idea of making a silk purse out of a sows ear. Yes, the Pono may have too thick of a top. It also may have too thick of a finish, be overbraced with thick sides and large kerfings, all of which will be detrimental to the sound. In luthierie, everything matters and everything is related. For an instrument to sound good you need a cohesive design with good construction technique. Wood is not an engineered material. One piece of koa may be the best thickness at 1.7 mm and another just right at 1.5 mm. If making a quality instrument were that easy, the CNC carving machines with their accuracy would have put the individual luthiers out of business long ago. Beginners have a difficult time understanding that much of what we do is an intuitive process, we have learned over time and many instruments what works for the individual luthier. Other luthiers do things differently, it works for them. Anyway get in there and build some instruments, find out what works for you.

Brad

Thanks for your input Brad. I think we are on the same page concerning my Pono. As cool as it sounds to have a cool laser-etched sound board on it, more than likely it will still sound about like it does now or worse and I will be out another $100. Probably best to just sell it on eBay, at a loss if necessary.

As for getting in there and building some instruments, I am definitely looking forward to it.

Hey Mike; Brad has pretty much covered the bases but I can speak directly to your Pono issues. I have a Pono tenor; Last years model before they started building the new lighter ones. It's not just the top. The whole thing is built 'heavy'. I was a carpenter many years ago so I know you know what that means..... it doesn't make it bad, just heavy. My Pono has great tone; it's just not very loud. The best solution is different strings. I put on the new Ko'olau ALOHI strings as recommended by MGM and it was a significant improvement over all the others I had tried. But it will never sound like a Koaloha or Kanilea which are much lighter built ukes. For example my Koaloha was built with no linings and on my Kanilea they are very small and delicate. Probably half the size of my Pono. Same deal with the bracing. I suspect they were built heavy on purpose to make them tougher and perhaps ease some pressures of the assembly process. You can read cost in all of that and when you start building you'll see what I mean.
So, as Brad says, dig in to it. It is a lot of fun.
Fred

Lot's of variations to the equation Mike.

Do you go with a thicker top, and very light bracing, or a very light top and more bracing? Each will give you different characteristics and dynamics, also affected by radius on the top and back, how thick the back is braced, the wood choice, strings, bridge....well you get the idea.

My exploration into this has lead me to using 6K Carbon Fibre Tow and Balsa lattice bracing on a top that has been taken down to 0.9 mm thick. Top is so thin that it's translucent when held up to a light. Better than a thicker top? Well, it's very loud, and very responsive, has great sustain, can be played with a light touch and driven very hard with lots of head room. But there are conventionally built instruments that would display similar characteristics in some areas, and perhaps each would be better in a different area.

Really, neither is better than the other, but just provides the builder an option for getting the voice that he is striving for, or rather attempting to achieve.

I like the laser etching idea....but not for the Pono. Where would you get that done??
I'd say forget the Pono and work on your own instruments.
You probably won't get a reliable answer on the top thickness question. Unless you build dozens of the same model you'll never really know.

Many sign and trophy making companies these days have laser engravers. Typically, you would bring them the instrument and an image file. The laser engraver works just like the old dot matrix printers. If the dot on the page is black, the laser is on and burns the wood. If it is white, the laser is off. I would imagine you would want to bring some sample wood to make sure how much power to burn with so it doesn't burn real far. If you go out to images.google.com and search for laser engraving wood, you will see some pretty cool examples.

It would certainly be interesting to see what impact it would have on the sound. At first I thought the thinner soundboard would make it louder, but I have also wondered if all the non-engraved areas would dampen the vibration because they would diffuse some of the board's vibration. I can see how all the components affect the final sound, thus making instrument building more art than science...more intuition than intellect.