Archtop considerations and hello

[malcolmw]

Hi all, first topic post as a recent member and novice luthier. Firstly, thanks all for the excellent forum that looks to have a fantastic lack of bad behavior and a great collection of information and advice, as well as all the enviable builds!

I am starting on my first archtop build but have a few considerations about timbers and process. I have talked to Trent at BGMS about it but thought it would be a good discusion here.

I am considering using New Guinea rosewood for the soundboard. This would be counter to traditional wisdom due to its density, but because of its amazing tap and the different setup of an archtop I feel it could be worth the experiment. I'll be attending Trevor Gore's masterclass which could provide some insight but would like to get started before that. Does anyone have experience using a hardwood for a top plate, or thoughts on it? Happy to be told its a silly idea.

On to carving, Ken Parker states in his videos that he initially glues up his plates with craft paper in the join so that he can break the join and re-glue after rough carving to, in my words, release the tensions with the new shape of the wood. This seems like a lot of extra work including making a jig to hold the halves for re-planing/sanding - has anyone tried this and/or have thoughts? Also, is seems that you may as well rough carve the two halves separately rather than gluing twice?

I also have questions about scale length and dovetail vs bolt-on neck, but they can wait for another post.

Cheers

Malcolm

[Clancy]

Hi Malcolm,

I've used Qld Kauri for the top.
It's now around 15 years old and I'm still impressed with the acoustic sound of it.

Never broken the halves & re glued, sorry.

[56nortondomy]

Hi Malcolm.
This is just my thoughts, I think if you're going to build an archtop which is a lot of work it'd be wise to use something tried and tested. I'm not saying ngrw won't work but it's a gamble. Spruce, WRC, Australian Red cedar, all better options I think.
Wayne

[malcolmw]

Thanks Craig and Wayne,

That's a beautiful looking build Craig - could you describe the tone? Is it cross braced or other, and do you remember what thickness you went to?

Wayne, hear what you are saying, specially as I have purchased fiddleback blackwood back and sides from David Linton that deserves care. It was actually David that put the idea in my head for the ngrw. Maybe the plan is to do the experimental build first with "lesser" back and sides and put the blackwood aside for the second one. I have an englemen spruce pair and some old growth red cedar that I can get a top plate out of. Was really looking for a slightly darker aesthetic so didn't want to go the spruce but the red cedar is very dark.

[lamanoditrento]

I have talked to Trent at BGMS about it but thought it would be a good discusion here.

Well, that’s one way to guarantee a reply. Name-drop me in a post and hope the guilt kicks in. It worked. Here I am.

Now, on the question of NGR for an archtop top: is it traditional? Not even close. Will it work? Maybe! The thing Trevor has hammered into all of us, gently, with a perfectly balanced mallet, is to build to the wood you’ve got. If it taps well and has the right properties, then game on.

That said, if you do ask Trevor directly, don’t be surprised if he slips into full Sergeant Schultz: “I know nothing! (At least when it comes to archtops)". But honestly whether flat top or arch, you’re still trying to get 5 grams of pluck to dance on 80 kilos of static tension. The rules of physics haven’t changed, just the shape of the dance floor.

Re Ken Parker and his craft paper voodoo… unless you’re wrestling with serious tension issues or have a burning need to disassemble your soundboard mid-carve like a tonewood jigsaw puzzle, it might be overkill. But hey, if it sparks joy and you’ve got the time, break the join and carve away.

As always: just build the thing And better yet, let us follow along. This forum is at its best when folks share their wild ideas, odd choices, and the glorious mess in between. Even the failures are useful. Especially the failures. (Just don’t ask me how I know.)

Looking forward to seeing this one take shape.

[Taffy Evans]

Hi,
I will contribute to this post because I love to build using NGR, but I will not be much help here as I have never built an archtop guitar. I did use it for a top once, but that was for a resonator guitar, so the sound quality would not be in evidence as the cone does the work.

I have used it for backs and sides, and necks for many years, first buying it about 18-20 years ago from my local hardware/timber store. Anything quarter sawn catches my eye, and interest, and a pile of New Guinea Rosewood did just that. It took me about a year to get all the stuff on the ¼, it was a big pile, and I had to keep an eye out for when the desirable boards, 50x300x2 m, became accessible.
This was before it became up for sale in tone wood suppliers’ catalogues, so I got it dirt cheap. I resawed it all myself into backs and side sets and solid guitar body blanks.

I have made countless guitars using NGR and all have put a huge smile on the faces of their new owner. One customer who has bought eight guitars from me, five of them built using NGR.
Theres not a lot I understand about what I have read about Trevor’s methods, that part of my brain must be missing…But I was encouraged to read that he advocates something I do understand and practice. “Build to the wood you’ve got”. Thanks for that, Trent.

Let us know how the NGR top goes; you never know, you could cause the price of that species to go up.
Cheers Taff

[malcolmw]

I have talked to Trent at BGMS about it but thought it would be a good discusion here.

Well, that’s one way to guarantee a reply. Name-drop me in a post and hope the guilt kicks in. It worked. Here I am.

Now, on the question of NGR for an archtop top: is it traditional? Not even close. Will it work? Maybe! The thing Trevor has hammered into all of us, gently, with a perfectly balanced mallet, is to build to the wood you’ve got. If it taps well and has the right properties, then game on.

That said, if you do ask Trevor directly, don’t be surprised if he slips into full Sergeant Schultz: “I know nothing! (At least when it comes to archtops)". But honestly whether flat top or arch, you’re still trying to get 5 grams of pluck to dance on 80 kilos of static tension. The rules of physics haven’t changed, just the shape of the dance floor.

Re Ken Parker and his craft paper voodoo… unless you’re wrestling with serious tension issues or have a burning need to disassemble your soundboard mid-carve like a tonewood jigsaw puzzle, it might be overkill. But hey, if it sparks joy and you’ve got the time, break the join and carve away.

As always: just build the thing And better yet, let us follow along. This forum is at its best when folks share their wild ideas, odd choices, and the glorious mess in between. Even the failures are useful. Especially the failures. (Just don’t ask me how I know.)

Looking forward to seeing this one take shape.

OK, thanks Trent, I have taken your directive on board and have started, soundboard is joined and Ive re-sawn a back and sides. Things have gotten a bit more crazy and I'm planning on it being a back-to-front guitar. That is, using red cedar for the back and sides and the ngr for the soundboard. I plan to build the back fairly lively to see how that contributes to the tone.

Now I will have to rethink the neck - was going to do a 5 piece incorporating ngr, blackwood and Cooktown ironwood, so now the body is ngr and red cedar is the red cedar too soft as a neck element?

On the neck, I'm thinking 635mm(25") scale length as a compromise between wanting the warmth of a shorter scale length against having a bit more room for my fat fingers.

[kiwigeo]

I plan to build the back fairly lively to see how that contributes to the tone.

Be careful with a live back. Suggest you read up Gore and Gilet for advice on tuning of back frequency.

[Trevor Gore]

...I am considering using New Guinea rosewood for the soundboard. This would be counter to traditional wisdom due to its density, but because of its amazing tap and the different setup of an archtop I feel it could be worth the experiment. I'll be attending Trevor Gore's masterclass which could provide some insight but would like to get started before that. Does anyone have experience using a hardwood for a top plate, or thoughts on it?

A quick and dirty way of comparing the potential performance of different woods is to compare their sound radiation coefficients, which is basically an index of the acoustical power that can be produced by a driven vibrating plate of a material. The number for NGR is about half that for spruce, meaning you have to drive it twice as hard to get the same power out. The sound radiation coefficient is computed as SQRT(long grain Young's modulus/density cubed), which demonstrates why light and stiff is favoured for sound boards.

I have used hardwoods for soundboards, but the way to make it work is to make the top panel the same mass as an equivalent spruce one (by thinning it out) and then use cunning bracing to get the stiffness back without much mass (e.g. by using a carbon fibre covered low mass lattice). However, bracing options are pretty limited for archtops, so you will likely suffer from low sensitvity unless you can come up with some smart way of bracing it.

Some more about the above approach here.