Official Luthiers Forum!

A lot of very knowledgeable posts here, which I've been reading with interest. I for one am completely convinced that an arched top is a stiffer top and more of an arch gives a brighter sound.

I have built relatively few guitars. When I started building, I read on the Internet that most hand builders are making their tops with about a 25' radius, so I have been doing that. Recently, I've noticed that the guitars that are the best musical instruments use a shallower radius, so I got a 40' dish. Maybe it will help my guitars be more like what I'm trying for.

Of course of course of course what I think is the best musical instrument is a subjective judgement. Furthermore, it could be a coincidence and it's some other factor that is explaining the differences I think I hear. And, in my hands, a shallower radius may not work the way it works on the guitars I've heard. Nevertheless, as a guitar maker I am responsible to listen, make my best judgements, and act on them.

From this perspective, the answer to the OP's question is that, as the top radius gets flatter or rounder the tone and (I think) dynamic response of the guitar changes a little bit. If you make it a little flatter, you'll probably need to add a little stiffness in some way (e.g., different wood, bracing, top thickness, etc,). When you reach the optimal combination of all the things that give you the appropriate stiffness, you'll get the right sound. The maker determines his, her, their, or its definitions of "optimal," "appropriate," and "right."

_________________
Tim Allen
"Never hurry, never rest."

Thanks for all the input.

So to add some fuel to the discussion. What about a flatter back vs a more radiused back? What if the radii of both are the same?

A good friend of mine is a full time contrabass repair guy. There is a version of uprights that have flat backs but with a standard top. They have a sound all their own but they are hardly inferior in sound to other basses, just different. I do think a flashback or flatter backed guitar would have a much higher propensity for cracks (those flashback basses I mentioned typically are giant potato chips and have many cracks) but from a sound perspective I'd be curious to know some thoughts.

I can say that my favorite guitar a 1946 J45 has a *very* tight radius to the top at 15' and the back is much flatter at maybe a 25' radius.

The upright bass is actually the bass member and modern survivor of the viol da gamba family. Originally they had a flat, or often 'cranked' back (with a fold in the upper bout to reduce the depth at the neck block), and a slope shouldered outline as opposed to the rounder 'viol da bracchia' shape of the violin. Early ones were tuned like a guitar or lute; in fourths and a third, rather than the fifth tuning of the violin, and gambas originally had frets. These days you see lots of hybrids; for example, with carved arched backs but the slope shouldered outline of a gamba, and no frets.

At one point I did a fair amount of bass repair. Basses don't get much respect, and you see some pretty crude repair work on them, even on good ones. I've seen them with the top nailed on with a little brad every three inches or so all the way around the edge: probably somebody who didn't have enough clamps or experience with hide glue. They're also quite lightly built for their size; I'm always amazed at how much of the weight of one is in the neck and fingerboard. And they're cumbersome. I once had a nice conversation with Joe Pass' bass player, who traveled with a $20,000 instrument. If you asked him how he liked airline baggage handlers he'd probably say;"Over easy with a side of fries". My hat is off to your friend: its hard to find a bass repairman, and most players only have one instrument, so there's a lot of time pressure too.

He's a very smart guy. It's a nice relationship because he'll share pics of his cool repairs with me and he's highly interested in guitar repairs. So I'll bounce ideas off of him on difficult repairs and he'll consult me with his guitar repair stuff. It's a win win.