Fate of the fibres, or carved vs. pressed tops

[RJVB]

Here's something I've been wondering about, and that I've mentioned in a few places already without ever getting a clear answer as far as that's possible:

When you carve a top (or the back) of an archtop you will be definition end up with a shape that cuts through the wood fibres/grain.

When making a flat top it should at least theoretically be possible to use a piece of wood where the brunt of the fibres run parallel to the surface, giving you a structural continuity (probably from front to tail).

Is that something to strive for in a flat top, or on the contrary, to be avoided? If the former, wouldn't the properties that make this the better top be preserved when you press it into an arched shape - and wouldn't that thus yield a better top than a carved one?

[IndianHillMike]

Originally Posted by RJVB

Here's something I've been wondering about, and that I've mentioned in a few places already without ever getting a clear answer as far as that's possible:

When you carve a top (or the back) of an archtop you will be definition end up with a shape that cuts through the wood fibres/grain.

When making a flat top it should at least theoretically be possible to use a piece of wood where the brunt of the fibres run parallel to the surface, giving you a structural continuity (probably from front to tail).

Is that something to strive for in a flat top, or on the contrary, to be avoided? If the former, wouldn't the properties that make this the better top be preserved when you press it into an arched shape - and wouldn't that thus yield a better top than a carved one?

I think one thing to keep in mind is that an archtop and a flattop have some fundamental differences in how they function. To over simplify, floating bridges with tail-pieces press down on the top while a pinned bridge pulls up on a top. With an archtop, you're relying more on the structure of the top to support the load while on a pinned bridge you're relying on the long-grain strength of the top and on the bracing. So, I don't think the sought after attributes of a flat-top are really applicable to an archtop and vice-versa.

[RJVB]

I was thinking in terms of acoustic sound quality, but yes, the thought did occur to me that a carved shape that cuts through the wood grain might have a different stiffness, possibly higher (I'm thinking of the stacked steel bar kind of suspension you see in older trucks).

Archtops do also rely on bracing though; I have no data that suggest that ones with a pressed top require heavier bracing.

[Alan Carruth]

The acoustic performance depends on the resonant pitches of the parts of the guitar, and how they work together. The 'wood' resonant pitches depend on the relationship between the stiffness and density of the wood. Wood is stiffest when the fibers run parallel to the surface, so cutting through the wood at an angle reduces the stiffness a bit at a given thickness, or requires a bit of extra material to get the stiffness back up to where you want it. Either way the sound is changed. I'll note that it takes a pretty large angle to make much difference in the stiffness of a top, though. We usually worry about run out in flat tops long before that point.

Arch top instruments have, of course, been made using tops that were bent to shape. Most recently we see this in 'affordable' factory produced archtop guitars and basses, but back in the day it was more common on some types of high-end instruments. Viols da gamba tended to use multi-piece tops where the central pieces were bent to rough shape and finish carved. A lot of such construction methods make sense if you take the mind set that wood was expensive and hard to get, while labor was relatively cheap.

Modern bent tops tend to be laminated, with cross plies. That more less automatically limits the performance IMO, due to built-in stresses and glue lines, if nothing else. There has been discussion in the violin world on and off for a long time about non-laminated bent wood tops. Advocates feel they should work better, but so far as I can tell no major benefits have been demonstrated. At one point some folks looked closely at some Stradivari instruments, and found no evidence that they were made of bent wood, so the notion has been pretty well dismissed in that corner of the lutherie universe.

[runamuck]

Originally Posted by RJVB

Here's something I've been wondering about, and that I've mentioned in a few places already without ever getting a clear answer as far as that's possible:

When you carve a top (or the back) of an archtop you will be definition end up with a shape that cuts through the wood fibres/grain.

When making a flat top it should at least theoretically be possible to use a piece of wood where the brunt of the fibres run parallel to the surface, giving you a structural continuity (probably from front to tail).

Is that something to strive for in a flat top, or on the contrary, to be avoided? If the former, wouldn't the properties that make this the better top be preserved when you press it into an arched shape - and wouldn't that thus yield a better top than a carved one?

What you're describing is called runout, where the grain isn't parallel to the face. The less runout, the stronger the piece of wood following the grain

Avoiding runout is why luthiers split wood for braces, in order for the face to follow the grain.

[Fathand]

Originally Posted by Alan Carruth

. There has been discussion in the violin world on and off for a long time about non-laminated bent wood tops. Advocates feel they should work better, but so far as I can tell no major benefits have been demonstrated.

At one time, I had a mandolin with a non laminated bent wood top. The top sunk

[RJVB]

Originally Posted by Alan Carruth

Modern bent tops tend to be laminated, with cross plies. That more less automatically limits the performance IMO, due to built-in stresses and glue lines, if nothing else. There has been discussion in the violin world on and off for a long time about non-laminated bent wood tops. Advocates feel they should work better, but so far as I can tell no major benefits have been demonstrated. At one point some folks looked closely at some Stradivari instruments, and found no evidence that they were made of bent wood, so the notion has been pretty well dismissed in that corner of the lutherie universe.

I was hoping to get a reaction from you

I didn't want to add laminate tops to the discussion because they're either used as a cheap solution to get a nice looking top (back) or as a (ditto) solution to fight feedback in archtops that are intented mostly for electric use. I also wanted to avoid confusion with "double tops" which IMHO are just laminates with a material like nomex as the middle layer.

My violin luthier (Jaap Bolink) told me about pressed-top bowed-string instruments the last time I went to see him; I'd been blissfully unware of them. According to him these are (or were) common among the lower and mid-end instruments and the fact they don't have a carved top can come as a real surpise given how nice they can sound.

[Quickstep192]

Steve Andersen experimented with a molded nomex double top.

I have a flat top guitar with a nomex double top and it’s great. I’d think a nomex double top archtop would be sensational.

[Silly Moustache]

Bon jour RJVB,

This doesn't really answer your question, but I made this video bout the two designs very recently which may be of interest.

Considering that you are in La Belle France, I apologise in advance tat I didn't mention the Maccaferri design.

[RJVB]

Originally Posted by Quickstep192

I’d think a nomex double top archtop would be sensational.

I think there are some (you'd have to ask around in the archtop section, or on jazzguitar.be). In fact, I know there's one, but it's a bit of an outlier:



@Moustache: merci, je m'en vais regarder ça!

[Robin, Wales]

I have an acoustic archtop made from 3mm cherry and maple plywood that's pressed to shape. The top has two parallel spruce tone bars. The back has no bracing. The guitar kicks out a good tone with plenty of volume and natural reverb.

So I don't think that there is a "correct" answer to the OPs question, beyond "it depends".

[RJVB]

Originally Posted by Robin, Wales

I have an acoustic archtop made from 3mm cherry and maple plywood that's pressed to shape.

Godin Kingpin or similar? The cherry+maple combo kind of implies Godin

I realise there may be no good answer to my question, if not only because no one ever tried to answer it empirically .

[Robin, Wales]

Originally Posted by RJVB

Godin Kingpin or similar? The cherry+maple combo kind of implies Godin

I realise there may be no good answer to my question, if not only because no one ever tried to answer it empirically .

Yep, it's the acoustic version of the 5th Avenue. It took some experimentation to find the bridge, strings and pick to drive the guitar, but it does really spit the notes out, albeit in a very unsophisticated way!

I'd like to play a carved top, and a birch pressed top, alongside my plywood top. I'm really not sure which I would pick?

[RJVB]

Originally Posted by Robin, Wales

I'd like to play a carved top, and a birch pressed top, alongside my plywood top. I'm really not sure which I would pick?

You describe well the reason why I didn't spring for a Godin

There's what looks to be a very nice carved top archtop in the UK on Reverb right now, a vintage L48, I'd drive 100km just to go try that one Barring that, I think the best budget carved top option that is normally not too hard to find would be the Loar LH600, or even the LH3x0 (laminate back). No idea about birch pressed tops though. I had a vintage German archtop in what looked like birch (possibly plain maple) for a while (Troubadour brand which was made for the UK market by Kirschnek) but I'm pretty certain it was all laminates.