Small (very) acoustic archtop design questions

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Small (very) acoustic archtop design questions

Postby james inkster » Mon Dec 02, 2019 7:13 pm

Hello!

I'm embarking on building myself a small acoustic archtop guitar, out of necessity.
I was an avid guitar player until about 5 years ago, when I had major reconstructive surgery on my right shoulder.
Since then I haven't been able to play guitar for more than a few minutes without causing days of pain.
I play a lot of clawhammer banjo though, using 11" and 12" pots (noting that the 11" feel more comfortable), tucked under my right arm, with the neck extending out from (not across) my body.

I've been playing a bit more guitar lately, having found that my 16" lower bout 3" depth (at the tail, not counting the top/bottom plates) archtop guitar is slightly more comfortable than my various flattops.

So my big idea is to try to build a 13.5" bout archtop (ala Gibson L1), trying to keep it as thin as possible (even thinner than 3" if possible) while also maintaining an interesting, big sound.

This is probably impossible, but I'd like to try as I'm running out of other options and thinner electrified instruments don't work for our genre of music.

Does anyone have any ideas/suggestions how to proceed?
I've selected some nice flamed maple for the back, and a sitka spruce top.

I've been thinking about building a guitar who's depth tapers from the tail (shallower -- 2") to the neck (deeper, 4"). I've never seen this before, but I am curious if it might work, given that most flattops are built with the opposite taper. Is this a terrible idea?

I'm also considering building the vertical wedge in it (manzer style), although I think the tail->neck taper is more what I need for comfort.

Sorry for the long-winded post, and thanks in advance :)
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Re: Small (very) acoustic archtop design questions

Postby Mike Conner » Mon Dec 02, 2019 7:34 pm

My GOM plan is essentially a 14.5" wide and 2.5" side depth archtop guitar. I built to a 23.5" scale length. So far I have completed two octave mandolins (8 strings, 4 courses) and one guitar. The guitar uses the 23.5" scale length and a standard 1.680" nut width. Has a great sound and plenty of volume even with the smaller size.

The plan is available on MIMF with the proceeds benefiting the site, so no financial interest for me. Hope this gives you some ideas.

A137 - Finished, Cutaway side, Sunlight.jpg
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Re: Small (very) acoustic archtop design questions

Postby Barry Daniels » Mon Dec 02, 2019 7:58 pm

I wouldn't be so quick to dismiss the Manzer wedge. It was designed to address the issue you described. And it does not reduce the interior volume of the body, which can't be said for your initial solution.
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Re: Small (very) acoustic archtop design questions

Postby Marshall Dixon » Tue Dec 03, 2019 12:09 pm

james inkster wrote:
I've been thinking about building a guitar who's depth tapers from the tail (shallower -- 2") to the neck (deeper, 4"). I've never seen this before, but I am curious if it might work, given that most flattops are built with the opposite taper. Is this a terrible idea?


Art Overholtzer, in his book on classical guitar making from the 1960’s, states that he built his guitars with a reverse taper as you describe (though the dimensions differ). As I recall, he was after a megaphone effect; didn't credit himself with this innovation, but said other makers were doing this also.

I have two guitars on the bench now that incorporate the feature. For now I'm going with it not being a terrible idea.

My experience after 26 acoustic guitars is that I like the overall sound of a thinner body. And, of course the ergonomics.
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Re: Small (very) acoustic archtop design questions

Postby Alan Carruth » Tue Dec 03, 2019 12:52 pm

The 'Manzer' wedge (actually patented by Smith) is probably just what you need. 1" of sideways taper (make the treble side 1/2" deeper and the bass side 1/2" shallower), is the equivalent of reducing the width of the lower bout by 1", more or less. It's easy to do, too.

My most recent archtop was based reasonably closely on a Gibson Lloyd Loar from the 20s, and was intended for acoustic use. It seems to have been successful; at leas the customer likes it. I used the 'full' style of arch that Gibson uses, although not as extreme, and 'parallel' bracing rather than the X that I have been using. The F-holes are also quite narrow, which helps keep the 'main air' resonant pitch down ti a more 'normal' guitar like range. It is 17" across the lower bout, and you'll want to go smaller, but I'd stick with those main lines of features.

You may also want to reduce the thickness of the plates from the usual, to drop the resonant pitches somewhat. If you do, use a lower arch height in proportion: too high makes the sound 'harsh' with light graduations. I've made two arch top classical guitars, on a 16" platform, with tops that were 'reverse graduated': 3mm thick over all with a thinner area down the center line in the middle. I used a 15 mm arch height as measured off the table: 12 mm up from the low point at the edges, and 'curtate cycloid' cross arches. There has been no problem with the top sinking under string load, ; just juggle your neck overstand and bridge height to get the break angle down to a minimum of about 6 degrees.
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Re: Small (very) acoustic archtop design questions

Postby james inkster » Tue Dec 03, 2019 3:51 pm

Wow, thanks for all the great replies.

I will definitely not discount the wedge, as I know it was designed for shoulder issues (though not necessarily the same shoulder issues..). I had previously done some tests trying to emulate how the wedge would feel using my flattops and it didn't seem to help much.
The key for me seems to be a shall tail.
However, that's also the reason I'm lately drawn to the archtop -- the tail is naturally shallower, building up to the arch, which i find quite comfortable.

I'm sure I'll have many more questions, thanks for the help.
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Re: Small (very) acoustic archtop design questions

Postby james inkster » Tue Dec 03, 2019 3:51 pm

Mike Conner wrote:My GOM plan is essentially a 14.5" wide and 2.5" side depth archtop guitar. I built to a 23.5" scale length. So far I have completed two octave mandolins (8 strings, 4 courses) and one guitar. The guitar uses the 23.5" scale length and a standard 1.680" nut width. Has a great sound and plenty of volume even with the smaller size.

The plan is available on MIMF with the proceeds benefiting the site, so no financial interest for me. Hope this gives you some ideas.

A137 - Finished, Cutaway side, Sunlight.jpg


Hi Mike, where on the site do I find your plans?
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Re: Small (very) acoustic archtop design questions

Postby Barry Daniels » Tue Dec 03, 2019 5:05 pm

Just remember that even though the archtop tail is rather thin, the distance from the high points on the top and the back is not any thinner than a dreadnaught due to the arched plates.
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Re: Small (very) acoustic archtop design questions

Postby james inkster » Tue Dec 03, 2019 5:33 pm

Barry Daniels wrote:Just remember that even though the archtop tail is rather thin, the distance from the high points on the top and the back is not any thinner than a dreadnaught due to the arched plates.


Yup, for sure.
But to get my point, grab an archtop guitar with a ~3" tail height and place your hand at the bridge. Take a look at the angle of your shoulder.
Do likewise with a dreadnaught (4"+).

For me, although neither feels wonderful, that extra angle makes a world of difference on my shoulder...
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Re: Small (very) acoustic archtop design questions

Postby Barry Daniels » Tue Dec 03, 2019 6:38 pm

An archtop has a 3" tail but the back and top arches add another inch and one half for a total of 4-1/2" and the bridge adds another 3/4". But I am not trying to be argumentative. If the thin archtop works for you then go for it.
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Re: Small (very) acoustic archtop design questions

Postby james inkster » Tue Dec 03, 2019 6:58 pm

Barry Daniels wrote:An archtop has a 3" tail but the back and top arches add another inch and one half for a total of 4-1/2" and the bridge adds another 3/4". But I am not trying to be argumentative. If the thin archtop works for you then go for it.


Yes, I really do understand that (I have an archtop guitar :) ) and I can assure you that the one hurts much more for me than the other.

Did you try draping your arm over a dreadnaught and then over an archtop to see the difference in arm angle?
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Re: Small (very) acoustic archtop design questions

Postby Barry Daniels » Tue Dec 03, 2019 8:49 pm

Yeah, you are probably right. The arm contacts the edge of the guitar and an archtop definitely has a lower edge. Sorry. I wasn't looking at it that way.
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Re: Small (very) acoustic archtop design questions

Postby Mike Conner » Wed Dec 04, 2019 8:39 am

james inkster wrote:
Mike Conner wrote:My GOM plan is essentially a 14.5" wide and 2.5" side depth archtop guitar. I built to a 23.5" scale length. So far I have completed two octave mandolins (8 strings, 4 courses) and one guitar. The guitar uses the 23.5" scale length and a standard 1.680" nut width. Has a great sound and plenty of volume even with the smaller size.

The plan is available on MIMF with the proceeds benefiting the site, so no financial interest for me. Hope this gives you some ideas.

A137 - Finished, Cutaway side, Sunlight.jpg


Hi Mike, where on the site do I find your plans?


James: The link is available at a couple of places from the Board Index. The plans are here:
https://www.mimf.com//phpbb/viewtopic.php?f=15&t=1465

I also have posted a Archtop Build Journal on MIMF, found under the Detailed Builds/Tutorials section, here:
https://www.mimf.com//phpbb/viewtopic.php?f=59&t=4668

Hoping you will share your build process details with curious folks like me!
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Re: Small (very) acoustic archtop design questions

Postby Alan Carruth » Wed Dec 04, 2019 1:55 pm

The arm angle is the whole point about the wedge, of course. The depth of the box along the center line is the same as always, and so is the box volume, it's just easier to reach around it.
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Re: Small (very) acoustic archtop design questions

Postby John Clifford » Wed Dec 04, 2019 7:30 pm

I made this parlor-size acoustic archtop. Lower bout is 13.75." Side depth is standard 3". It has a cedar top and sapelle back & sides. The top has a relatively low arch (about 5/8" from bottom to top), and I used parallel bracing. It's quite loud and has a nice snappy sound. It would work fine for acoustic music jamming. So I think what you have in mind is definitely workable.
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