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I need to build an carved archtop. Why? I do not know.
Now with that out of the way, I have a stick of wood that might make an interesting instrument. I do have to massage it into shape, will work that out when I have time. It probably will be 14.5" - 15" for the lower bout and 19' body length, scale length roughly 25". Might do a cutaway, might not, want it to be mostly an acoustic instrument. I have gone through the builds here and am not sure about the profile of the plates. I am guessing that a smaller instrument would have a slightly shallower dome (for lack of a better word) than a 16-17" instrument. Also the thickness of the plates might be less in order to get some bass out of it. But I am only guessing. I do have some better wood that can be used for a larger instrument but the piece I want to use is a "I found this xxxxx, I wonder what I can build out of it?" The back and sides probably maple or cherry, maybe a cherry neck. I have built a few flat tops so this is not my first instrument but first time carving one. I may be a little slow out of the gate on this one as I am building two guitars at the moment and want to use the time before they are done to learn a little before I jump into the deep end of the pool.
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03-14-2023 12:26 PM
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I recently (one year ago) built a 16 inch archtop. I have a fair bit of experience with flat topped acoustics and a few carved topped electrics but this was my first experience with a carved acoustic guitar. I basically followed Benedettos's arching scheme, shrinking the dimensions from 17 to 16 across the lower bout.
I'll be perfectly honest - I have not completely bonded with this guitar. It is very bright, almost shrill altho it has mellowed over the year. I spent a long time experimenting with strings but finally have settled on something I like (the new D'Addario coated XS PB's). It is very possible that I simply do not have enough experience with this style of guitar and that the voice is "normal", it definitely is loud and there is very good note definition within chords.
Since I have no idea of what I was doing but do have some computer software that lets me grab sound samples and convert them to the frequency domain, I was able to hear and see the changes as I carved the top. I X braced it and ended up pretty close to Bob's thicknesses - clos to 1/4 in the center and 1/8 inch along the rim.
I happened to have a pressed laminated mahogany back with sort of dictated the size
Here is the guitar
I did do a build thread at a different forum if you are interested. It has a lot of the voicing information but as I said, I don't know it I was really sucessful.
Lets build something that looks like an L5 archtop | Telecaster Guitar Forum (tdpri.com)Last edited by Freeman Keller; 03-15-2023 at 07:56 PM.
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It may help immensely to make an online study of KEN PARKER ARCHTOPPERY tutorials. He takes it step by step from conception to finale. Mostly in real time.
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I saw your thread over there, skimmed it but need to read through it.
Originally Posted by Freeman Keller
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I caught a little of his Youtube series but put it aside as I was not building one at the time. Thank you for reminding me of it. Originally Posted by ArchieHollow
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Mr Parker explains it all... dimensions, geometry...even how to make your tools. He's an excellent teacher and guide
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One of the most important tools was the little thickness gauge that I made from a bridge clamp Originally Posted by Printer
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I’ve built several acoustic archtops, as well as had the benefit of helping teach archtop guitar building for a local community collage. It’s been my good fortune to see and be involved with probably fifty or more being made by others.
IMHO if you follow the Benedetto book you will have a very nice electric guitar. But it will be very tight and harsh as an acoustic instrument, as Freeman can attest to. You need a much looser and lighter top for an acoustic. I suspect the book specs were beefed up compared to his actual builds. Also, because of the way they project you really need a sound port to get a good idea of what your guitar sounds like acoustically.
I went on a multi-Year quest to get a good modern acoustic sound. Unlike a flat top, you can string up an archtop without glueing on the top. At the height of my obsession I took advance of that and made six tops for one test mule body.
I’m not a pro, and I only build as a release from a stressful office job; but it is in my nature to do things methodically. In a nutshell, I can say this:
1) The lighter the top and bracing, the better it will sound. The trick is finding the edge where the top won’t sink or, horrors, crack.
2) thickness is a function of the wood and body shape, but in general Benedetto is almost twice as thick as a good acoustic needs to be. A smaller guitar need geometrically less top strength or bracing.
3) a top needs to support 30lbs of down pressure. That’s putting your thumb on it and leaning in with some of you body weight. It should just lightly yield. The bracing is just there to support the top from deforming too much under string pressure, voicing comes from thinning the recurve.
4) X bracing on an archtop makes no sense to me and forced me to overbrace.
Good luck and enjoy your adventures!
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Can you discuss your thinking about this? Originally Posted by rlrhett
AKA
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Inquiring minds also would want to hear. Originally Posted by AKA
This is where things get weird folks. Rummaging through my wood pile and I think, "This is a pretty decent 2x3, I wonder if I could carve a top out of it?"
First thing is to rip it in half. The problem is it is sub-zero in my garage and the sheave on the motor cracked and took off my belt. I picked up a cheap table saw once when the motor went on another one I had (my dad made it, worked alright if you fiddle around with it). I was going to set it up just to do fretboards but have not done it yet. I ripped it in my basement workshop, fed it slow so that no big chunks decide to fly off. Used a square jig I made up once to joint with sandpaper when I did a build thread on making a guitar with few tools. Squared it up and made a featherboard of sorts on the other side to keep the stick against the fence, the 2x2 off to the side at a forward angle which snugs up the board when pushing forward. Stopped to take a picture just before I got through, the washed out picture due to all the fine dust floating around. We won't be doing that again.
Which brings me to why I am doing this right now. My house needs some major foundation work and I have to gut the whole interior. No idea when I will get back to building guitars so I am cleaning up projects before the summer building season. I collected light wood and with life not going the way I would like I have too much of it sitting about. One project I just about finished is a 2x12 cabinet that weights 30 lbs including alnico speakers, I am getting on in life and hauling heavy stuff lost its appeal. But back to the guitar. 19" long, just under 7 1/2" wide, less than that once I plane them down. Might split one to give one more row wide to get 15".
And once I have learned how to not make fatal errors I might just go on to make a more serious instrument. Mind you the 2x3 is pretty light, guessing it might be Engelmann spruce. It might work out as a home noodling guitar.Last edited by Printer; 03-17-2023 at 12:46 PM.
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I would be very interested in knowing what your targets are . How much deflection do you like and how do you measure it? What are your target thicknesses if Benedetto is twice as thick as it should be? (Benedetto calls for 1/8 inch in the recurve and 1/4 in the center). How much arching do you like? Do you measure the stiffness of your top wood, if so what do you like to see? Do you do any sort of tapping or other voicing and if so what are you listening for? Originally Posted by rlrhett
I doubt that I will ever build another one of these things but if I do I would like as much information as possible.
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Ok. That maybe requires an essay rather than a post. I can go deeper into it for you over at MIMF or OLF. We both seem to have the same handles here and there.
Briefly,
1) I pre-carve on a CNC to 3/16”. By hand I begin to thin around the dome as evenly as I can until I can press down with my weight on the bridge area and get about 3/16” deflection. Eyeball. I used to use calipers, measurements, and even would use a signal generator and hand hold the speaker of a small practice amp to produce Chlandi patterns to ensure an even carve. Frankly I grew to trust my “instincts” after a few years and gave up on the pseudo-science. Or at least that’s how I justify my laziness.
2) I brace (parallel). Flex again. Thin the braces until I get about 1/16” to 1/8” deflection.
3) spool clamp the top to body/neck (yes, neck.) Tap. Thin recurve. Looking for deep resonant sound. Occasionally remove top and press for deflection. Careful because cross grain strength in spruce/cedar/redwood varies a lot. Sometimes you need to thin the recurve at the tail more to try to keep it even. Also the temptation will always be to thin to the point of failure. I used to keep failed tops to learn from, but eventually they filled a trash can and went into a cathartic fire.
4) if you are super ambitious, you can actually spool clamp the whole body (back/rims/sides) and thin the recurve with the guitar strung up. I did that once, but it wasn’t really worth the hassle.
That’s it. No more science than that. A caliper tells me I’m in the .80” range in the recurve, but it varies so much between boards I don’t know if that is a useful thing to measure. A lot of listening to the wood, flexing it, seeing what it wants.
Starting with a rough carved top, not super time consuming. Almost more time preparing the blank from rough cut 8/4 spruce boards. I never bothered with expensive “luthier” wood.
In the end, I found at least, you have a guitar few people want. Dreds have scooped mids, boomy lows, sparkly highs. Perfect if you a James Taylor or Joan Baez to accompany your voice. An acoustic archtop has clear, clean, forward projecting mids. Not the best for cowboy chords, and not loud enough to play against a drummer and sax (or whatever). I love it because I like playing solo guitar (usually finger style) in a small venue. For that they are God’s voice.
Take this all with a grain of salt. Again, I’m a determined amateur, but still an amateur. I’ve learned by doing and by corresponding with professional luthiers like Alan Carruth.
YMMV.
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An arch top moves the top differently than a flat top. A flat top bridge twists the top, an arch top bridge pushes the top up and down.
The X brace of a flat top sits under the edges of the bridge. It transmits that twisting action to the sound producing part of the sound board south of the sound hole. That is not what you want the soundboard of an arch top to do. You want the soundboard of an arch top to move up and down as a unit like a speaker cone. The bracing is just there to keep the speaker cone from deforming under the constan 30lbs+ of pressure from the bridge.
In my experience parallel braces do not need to be as massive as X braces to do the same thing. Although, I have seen people put massive parallel braces in and I don’t know why.
As with all things guitar, the wood is more important than the rules. Maybe there is a situation where an X brace will make a better guitar. Maybe you are going to cut into the top for pickups and you need an X brace to clear the pickups. But for purely sound reasons I’ve never found that X bracing makes for a better acoustic archtop.
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RlRhett,
Thanks for the response. I’m having an acoustic archtop built (no pick-up floating or built in) and your comment caught my attention.
AKA
Originally Posted by rlrhett
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I am not sure if I would agree on the the flat top twisting the top and not acting as a speaker cone. Originally Posted by rlrhett
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Thanks for your comments, RIRhett, I wish we had had this disussion a year ago. I agonized over the choice of bracing for quite a while before making my decision. I understand the difference between fixed and floating bridge and the forces working on the top and had built an F5 style mandolin with "parallel" bracing. My idea with this guitar was that I would play in my living room and didn't need the power to cut thru a jazz band or a big room, and that while I wanted the "archtop sound" (whatever that means) but still with some warmth . I was influenced by what Benedetto said Originally Posted by rlrhett
"In general a thinly carved top with parallel bracing will produce a louder voice with greater projection than a thicker top with X bracing, which will typically produce a softer, mellow sound"
In a panel discussion about archtops at one of the GAL conferences Steve Grimes was asked the difference - he said that his preference was warmer balanced sound which he got with X bracing. He said "its not as quick , but has mor warmth and character" It seemed like most of the panele members were building X braced rather than parallel and in the end warmth won over loud.
I actually think my guitar might be better than I'm giving it credit, I think I'm probably not a good enough player to really appreciate it.
Any way If I ever build another it will be parallel braced and be thinned as much as possible, howeve I doubt that I will go thru the effort. Nott too late for Printer to make his decisions however.
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Freeman, if you are open to experimenting and don’t care about refinishing try carving the recurve a bit across the bottom third or so. Do you have one of those little violin squirrel planes? Just a few shavings. String it up again and see if you can hear a difference. You may find it warmer despite being a bit overbraced.
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Aw, was hoping you could go further with this, Originally Posted by rlrhett
"In general a thinly carved top with parallel bracing will produce a louder voice with greater projection than a thicker top with X bracing, which will typically produce a softer, mellow sound"
...also how a thin carved top with an X brace would compare with a thick top with parallel braces.
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Make both a see for yourself! As one friend said to me,
“Guitar making is 10% measuring, 10% cutting, and 80% SANDING!”
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Ok, maybe a less cheeky answer is this:
What I think is happening is that an X brace is less bracing for the same mass as parallel. The f holes essentially eliminate cross grain strength to resist the downward pressure of the bridge. The whole job of supporting the top falls on the long grain strength of the top, hence the parallel braces.
If you are going to use roughly the same sized braces, spreading them out in an X and not extending them as far would result in less strength. That might result in a “warmer” tone. But you still have the mass, so it would seem less lively.
My personal experience was that making much lighter parallel braces and thinning the recurve gave me better volume and balance than a heavy X.
I found no scenario where a thicker top lead to a better acoustic instrument.
But, again, I’m no GAL panelists. YMMV.
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I think I also owe this discussion a further explanation:
Looking for an acoustic archtop lead me to lighter and lighter top/bracing. Eventually I reached the limit of what spruce could do. I ended up experimenting with composite materials. I made a series of a half dozen guitars like the one pictured.
Since then I had a late in life child, and other than some nifty electric guitars for nieces and nephews I haven’t been building new guitars. I play a couple of my composite archtops every day. In fact I have one in my lap now. But like the dog who gets the car, I have my dream guitar and don’t know what else I would do. So now I try to just shut up and play. :-)
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Oh, and FWIW I didn't say that a flat top doesn't act like a speaker cone. Just that the bridge excites it differently. If you look at your pictures you will see that sand is gathering at the edges of the bridge indicating it is twisting or rocking back and forth. But, if you are interested in that stuff there are tons of resources on how a flat top vibrates. Here is a cool image of many:
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I agree with a light top, light braces also. I have looked at some of the X braces and the parallel (as well as angled), and the parallel braces were generally more beefy. But I still need to spend some more time learning if this is normal or I just happen to see one style of building. I got confused by your post comparing the X brace with a heavy top, whether it is a normal thing that X bracing needs the top to be heavier. Originally Posted by rlrhett
On the sand bunching up at the edge of the sound hole, not sure if this shows the top was pivoting due to the X brace as originally stated. Then there is the bridge at the center of the lower bout on 12 fret instruments. Not sure where the sand would end up at. The pretty picture of the Classical guitar is not really relevant when talking about the X brace, but it seems there is not many laser profiles done for X brace guitars. Darn students usually pick fan braced guitars to do their thesis on. I was planning on doing my own optical measurements of the guitar tops but due to life getting in the way I have lost a number of years where I should have been playing. I might do it yet.
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The pic is one of Guillaume Rancourt's instruments in progress. This bracing is actually carved into the inside of the archtop. It's sculpted into the same soundboard, instead of gluing additional wood to act as braces on the structure. The carved arcs appear to be sort of a combo of X-bracing and parallel bracing. I'm using it in a parlor-size hollow body guitar I'm currently building
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How the strings pull on a pinned bridge vs push on a floating bridge is not really a function of the bracing. It's not usually a controversial topic, and in my experience a relatively accepted function of physics; but what you do with that information is totally up to you. I've shared how I apply and think of it, but I've got no dog in this hunt. There are as many theories about how to build as there are luthiers.
The point is to go out and experiment and build. You are the luthier, you don't need to do it the same as anyone. As I used to tell my students, the worst sounding guitar is the one that sits uncompleted in pieces in your garage. I can't wait to follow your build thread and see what you come up with!
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