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I'm not quite sure how to describe this, so bear with me...

I've seen lots of innovative bracing to counter the twisting at the neck join - flying butresses /suspended bracing and such like.

I've never seen any novel bracing ideas to help with the down forces on the top. I'm thinking of something like carbon fibre which is held in tension and prevents the sides from being pushed outwards as the bridge is pushed down by the strings. It would be attached to the sides just under the top (but far away enough for it to vibrate freely) and run approximately under the f holes, ie between the two widest points of the lower bout.

Something like this:


Carbon fibre in tension holding the sides in would help the sides remain 'vertical' and help the top maintain it's arch.

Just thinking out loud.....

Maybe some of the other archtop makers will chime in here but you might be addressing a problem that in reality does not exist. You also have to think about accessibility for repair or pickup placement in the already limited access provided by f holes.

Is the guitar pictured one with a flat back and arched top? Carved or laminated?

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Terence Kennedy wrote:
"..you might be addressing a problem that in reality does not exist."

That's my opinion. So far as I can see, a top that sinks a lot over the 'medium' term is probably either too thin, badly shaped in terms of the arching, or has excessive break angle over the saddle producing a high down load. Spreading of the sides is not an issue that I can see, so putting in a 'collar tie' probably won't help. I've only been making them for about 40 years, so I can't say much about the long term from personal experience.

My archtop ROSE.

Once it did that it's been stable. It did raise a little more when I put stiffer strings one. But it hasn't moved at all since then

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Why be normal?

Beautiful work John.

I agree with the others as a repair guy we frequently work on arch tops that are approaching a century old and never had this problem.

Check out the work of Howard Klepper specifically his use of cylinder tops, flying buttresses and fully length CF suspensions. I have a feeling you will find it interesting even it if it is not technically an arch top.

Hi Terence, yes flat back and carved top. It has a soundhole rather than f holes so access is a bit easier, albeit a very thin body (55mm) so still not that straightforward. It will be an archtop bass so for bass response I need to make the top as responsive as possible without it collapsing. So my thinking is to make sure that the dome is supported as much as possible by the sides.

I have enough problems dealing with real problems building guitars, I really shouldn't create new ones.

Hi Ken, was your assumption that this was caused by the rotating forces from the neck joint? I could see how that could potentially cause the top to rise.

Thanks Alan. I've started building acoustic bass guitars, designed either to be amplified or to provide enough acoustic volume for solo practice. As a player I've found playing an acoustic instrument completely inspirational. The immediacy is something we bass players are not used to. So I'm trying to get as much response from the top as possible, which inevitably means pushing closer to the physical limits than is necessary with 6 string guitars.

Here's a previous prototype:

Thanks Hesh, yes really interesting work from Howard Klepper.

Apparently MANY things are going on. The belly wood of the archtop is curly redwood, so, it might like to bend. I have some violins and violas that have risen, and the projection dropped. More than halve of them, including a cello haven't moved at all. So I don't have a clue of what to do to keep the neck block from rotating. I don't know why most have no problem, but others do. What is different?

I don't think that it is just the neck bending. The belly can't rise too much if it isn't being squished by the north/south pull of the strings.

Acoustic bass sounds like a cool thing. Bass lines are what I hear in most songs; at least older songs. The new stuff doesn't have bass, harmony, or even melody!

I have really stiff Doug fir that I was thinking of making into a 12 string archtop with a low arch. But an acoustic bass might give about the same string load? A 5 or 6 string?

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Why be normal?

A light 4 string bass has very similar string tension to a medium strung 6 string. There are 5 and even 6 string basses in existance (Warwick Alien springs to mind) but from the online videos I've seen they sound pretty terrible when acoustic. A low B seems like a an impossible wish on an acoustic....