Official Luthiers Forum!

A client asked me this question yesterday, "do you think it's possible to make a professional sounding instrument out of plywood?"

My answer after some thought is... Yes. Kind of. But why?

I've not gotten the why yet but my guess is for traveling purposes. He's a fairly well known blues player and travels quite a bit. My thoughts... There are already well known luthiers building with laminate sides and even backs. I've built Selmer style guitars that are all laminate with solid tops.

My guess is that an all laminate guitar with a double tops sandwich top or what ever you choose to call it with a Nomex core would not only sound good but would be more weather resistant.

I have never built a steel string double top but have built a classical double top and it was a decent guitar, not great, but okay.

I just wonder what y'alls thoughts are.

And BTW I have played some surprisingly good plywood guitars over the years too. I'm just not sure I could build one well.

I think the client’s question is burdened by imprecise language. “Professional sounding” is a pretty squishy phrase. There are professional musicians who use off the rack POS factory low end guitars. And if they use pickups, the acoustic tone of the top (solid or plywood) may not matter too much for the job the guitar is meant for. So, I don’t fully appreciate what “professional sounding” is supposed to convey. Moreover, blues guitarists often use guitars with a limited tonal range, on purpose. I think you would benefit from talking to the client a bit more. After all, if they want something that an off the rack POS factory guitar can provide, maybe that is a better choice at a better price.

I'm under the assumption that 'professional sounding' means something with decent tone. I'm restoring an old ladder braced Gibson LG0 for him now. Now that's a blues guitar! And yes I know a few incredible guitar players that are perfectly happy with a plywood Fender and can make them sound better than anyone who can afford a Somogyi. I will of course open up a dialogue with him but I am just curious as to other fellow luthiers thoughts or even better, experience.

"Professional sounding" is a pretty low bar. Yamaha has been building plywood guitars for decades that have been used by professional musicians, because of their lower cost and durability. Some of them sound quite nice.
Although I often build with HPL and laminated sides and back, I use "solid" top materials. I think plywood would be more difficult to work with to get the same quality of sound.
I would think a Nomex core top would be more delicate and much harder to repair than a solid wood top. I think one reason plywood guitars have a reputation for durability is they are heavily built and that we tolerate the scars they receive without bothering to repair them. When they are completely trashed they go to the landfill without much heartache. A lot more plywood guitars have come and gone than Martin's.

A few years ago I saw David Chapdelaine at a small reception/recital. He was gushing about his double top nomex guitar as the future of acoustics. The guitar that he was using was coming apart at the seams.

We recently built a laminated back/sides with nomex core double top flamenco guitar. Unfortunately the double top was not glued properly in a couple of spots revealed by tapping. We replaced the top with a spruce/cedar laminated top (no nomex) as an experiment. The guitar turned out excellent and the new owner is delighted with it.

I would not use a double/sandwich top on a touring guitar. They use very thin outer skins that are easy to punch through, for one thing.

Also, I did some experiments years ago on Nomex sandwich construction. Test panels that I made with deliberately bad glue areas could not be distinguished at first from presumably 'sound' ones. Vibrating the test panels hard for a time loosened up the bad area, so that you could hear scratching noises when they were pressed in those locations. More driving extended the loose areas. Although I did not run it to destruction (it was noisy) it seemed to me that over time the loose areas would extend to an edge, which would allow the skin to buckle in compression, and the plate would fail catastrophically. When I mentioned this on a guitar group on line I got an e-mail from a well-known dealer saying that he had seen just this sort of failure.

Plywood B&S is, of course, a proven construction. My experience has been that new guitars with ply tops can sound quite good, but that they don't age well. I imagine that humidity changes set up stresses in the glue lines between cross plies. Even if they don't fail by delamination the stress itself could hurt the sound. Also, plywood has higher damping than solid wood, and recent testing has shown that high damping hurts the sound.

If you’re looking for touring stability, I wonder if torrefied woods could be useful?

I'd worry about the fracture resistance; the Torrefied wood I've worked with has been very splitty.

Lowden makes a Jon Gomm Hybrid (laminated spruce/cedar) Top signature acoustic that sounds more than tolerable -
https://www.youtube.com/watch?v=fFILG25sgus
Laminated sides are quite common and can improve sound, Tom Sands laminates backs with a decorative but "dodgy" (e.g. heavily spalted) woods using structurally sound woods.
Why on earth not?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

So why did you go with that design? Was it for stability purposes? What glue did you use for the laminates?

I wonder too if perhaps a thick spruce top and a very thin plywood top would help for stability and tone?

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The double top classical I built is probably about ten years old now and back then it was recommended to use either epoxy or Polyurethane Gorilla like glue. It didn't seem like a good idea to use Gorilla so I used West epoxy.

It was strictly an experiment. We had built several very successful double tops with nomex and I wondered what a spruce/cedar laminated top would sound like. It turned out excellent. We explained to the customer that it was experimental and gave him a substantial discount. He has now been playing it for about 2 years and is still delighted. We used West epoxy for all the laminations. I've reached the age where I don't care if a guitar sells or not so we do a lot of experimenting. Sometimes the experiments give surprising results but most don't.

As much as I respect Mr. Carruth's vast knowledge, I had no trouble at all determining that the original top had a couple of spots with glue failure just by tapping on it.

jshelton wrote:
"I had no trouble at all determining that the original top had a couple of spots with glue failure just by tapping on it."

I think you got lucky.

When Nomex core construction first came out a manufacturer designed a light airplane with Nomex core wings and aluminum skins. The FAA would not approve the construction unless they could come up with a method for finding voids in the glue line. Eventually they came up with an ultrasonic tester that could do it, and now it's a common feature of many aircraft. I don't think it would work with wooden skins though.

Bottom line Yamaha, all some form of plywood? No need for a luthier to invent something that can be bought for cheap.

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Peter Havriluk