Double top all-wood acoustic

[Frederich Holtier]

Hello everyone.
After making DT classical guitars (Nomex or all-wood) for more than 18 years I decided 3 years ago to build a few acoustic guitars using the same method.
Basically is a 2mm thick top on which i CNC machined about 900 1/4” holes 1,5mm deep and then laminated a thin 0,5mm venier to close the holes.
Here are a few photos of the guitar in working process.
The first photo is a classical all-wood top. It shows better the way is done.
The same process is applied to the acoustic guitar top.

[Peter Wilcox]

So what does it do to the sound? Why wood vs Nomex? Why 0.25" vs another size? Why 1.5mm deep vs 1mm or another depth? I'm just asking, as I'm unfamiliar with double top instruments. It seems like a lot of trouble unless there is a significant audio improvement.

[Andy Bounsall]

Interesting, but...what Peter said.

[Frederich Holtier]

Ok. The 0.25” holes and the 1.5 mm depth gives me the best ratio of weight and stiffness of the machined area. Bigger holes will weaken the top, smaller holes will not remove enough wood to make a difference.
I started experimentig with this design in 2001 and for 2 years i tried all kind of versions untill I decided to this one. The wod DT has only one glued surface, the Nomex has two. As i mentioned, I build this design also with Nomex, but I think the sound of all-wood tops is more natural. Besides more power, the main gain is in the outstanding clarity, responsivness and the balance between trebles and basses. The inside lamonation acts like a large very low brace, reducing very much the need of heavy bracing.

[Peter Wilcox]

Thanks Frederich. Do you have any links or clips of the steel string guitar being played?

I see you use double-x bracing in your guitar that are thickened where they span the area of holes, to give extra strength there I presume.

[Clay Schaeffer]

Do you ever worry about pick scratches?

[Frederich Holtier]

Peter, sorry , I don’t have any recording of my acoustic guitars so far.
It’s also true that aren’t to many out there, since I build mostly classic.
Regarding the pickguard, I don’t really like them.
Most of my customers were fingerstyle players, so no one requested.
For the pick users I could use some clear material, the same i use for flamenco guitars.

[Ken Whisler]

Hello Frederich,

Serendipituos timing here, as I've been both reading up on the tech and visualizing the process to possibly apply to my own work.

I tried a nomex top @12 years ago. It delaminated on me before I even got it strung up. So I re-topped it with a conventional top and shelved that idea. Around that same time, I was in a friend's store, and he was showing me a new arrival by >insert name of fairly well known double top maker<, and although brand new, it had delaminations. Add to that, there were rumors in the circles that Scott Tennant's Dammann was delaminating. I heard Scott perform with that guitar in a very unforgiving hall, and it sounded good, but not that much better than many of the traditionally built guitars I've seen in that same hall. OTOH, I saw Andy York in that same hall with a Dammann, and it sounded superb. But still, I pretty came to the conclusion it was not worth the extra effort.

So 3 things happened to give me thought to give it another go:

1) I talked to a few players, and their attitude was double top construction afforded them the luxury to relax quite a bit when performing; they did not feel the need to whack their instruments into oblivion to project to the back of hall and sacrifice a lot of dynamics.

2) All wood double tops starting appearing. To my ears, these have a much wider range of timbre.

3) I have access to a CNC router.

Although the CNC machine I have access to is geared towards large format printing (It'll do a 4X8!), I've seen the detailed work done on it, and I've already visualized many ways I can use it to apply to my own work. And it's free, .

When I read up on what others are doing in this realm, it seems they all have been treating it just like nomex; two outer skins and a core. Of course I know that's necessary when using nomex, but I've been thinking it sounds redundant when utilizing an all wood construction. I'm thinking to myself, "Why not just route -1- solid top and glue another top to it?!?!" Afterall, the objective of the double top is to reduce weight to increase volume and resonance, and if one reduces the layers from 3 to 2, one has just eliminated half of the glue used, right? (Yes guys and gals, double top makers obsess over weight to the point they weigh the amount of glue used).

I'm assuming the routed top is the inside top, correct?

Be honest: any delams happen to you, yet?

And thanks for sharing your experience.

[Frederich Holtier]

Hi, Ken.
The outside top (2mm thick) is the one machined. The inside is just a thin, 0.5-0.6mm, piece of spruce laminated over the holes.
I built the first DT in 2001 and since then many dozens of Nomex and all-wood tops. I never had any problem with delamination.
The way I designed my tops, there's not stress on laminted areas. The bridge is always glued on a solid part of the top, no machining under the bridge
in both models, Nomex and all-wood.

[Ken Whisler]

Hi, Ken.
The outside top (2mm thick) is the one machined. The inside is just a thin, 0.5-0.6mm, piece of spruce laminated over the holes.
I built the first DT in 2001 and since then many dozens of Nomex and all-wood tops. I never had any problem with delamination.
The way I designed my tops, there's not stress on laminted areas. The bridge is always glued on a solid part of the top, no machining under the bridge
in both models, Nomex and all-wood.

Thanks, Frederich!

Have you seen examples of the delams I talked about in the work of others? Unsightly little bubbles.

[Clay Schaeffer]

Has anyone experimented with doing an all wood "double top" construction but leaving off the inner skin. Would it reduce the stiffness that much since the honey comb drilling would form a "lattice"? You could avoid the weight of the glue and the second skin.

[Frederich Holtier]

Ken,
No, i didn't see delaminated tops. I had in my hands only the David Russell’s guitars and they were fine.

Clay. A top without the inside layer won’t work. It’s to week, it doesn’t work like a lattice. What is left after machining has all the fibers interrupted.
Only after lamination, the top will regain the strenght, the walls of the holes are only spacers between the bottom of the holes and the glued lid of the holes.

[Chuck Morrison]

I've been building double tops for a six or seven years now. I appreciate seeing how you've done the CNC work on your wood DTs, and had conversations with builders who have been doing that or talked about doing it, but I haven't had the opportunity to see one or try it myself. My concern about doing it is that the wood honeycomb (or whatever shape the holes might be) sections that remain would have a tendency to break/crack along the grain given how thin they must be. I'm assuming that they must be much thicker than the paper thinness of Nomex. I'm wondering how you have dealt with that possibility?

[Clay Schaeffer]

Ken,
No, i didn't see delaminated tops. I had in my hands only the David Russell’s guitars and they were fine.

Clay. A top without the inside layer won’t work. It’s to week, it doesn’t work like a lattice. What is left after machining has all the fibers interrupted.
Only after lamination, the top will regain the strenght, the walls of the holes are only spacers between the bottom of the holes and the glued lid of the holes.

That makes sense. I hadn't thought about that.