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I've recently strung up an archtop bass I've been working on. It sounds fine, but I want to see if I can push the bass response a bit further by working on the recurve a bit more.

I realise archtop basses aren't the same as archtop 6 strings, but would any archtop builders care to give a few pointers about how you approach refining the recruve once the strings are on? Do you follow set measurements or do it by ear, or use tap tones, or measure changes in the various resonances? How do you know when to stop? Do you scrape, sand?

I don't know whether I'm being blind but an internet search doesn't really bring up much of any help.

Here's the build:




Just to clarify, my goal is not to increase volume. I'm not trying to build a bass that will be played acoustically with other instruments. I want a bass that sounds great for solo practice, and it will also have a piezo under the saddle. So I want to increase bass response, not volume.

The top is carved from 4mm in the centre to 3.2 mm around the perimiter without the recurve. The dome is low, 12mm, and the braces are light. I've been really inspired by Ken Parker.


Any pointers really appreciated!

I’m no pro but have built a couple of acoustic archtops with floating and K & K pickups as well. They compete very well in an acoustic jam. Dimensions and construction tips were generously provided by Bill Moll on the MIMF way back when. These are 20” lower bouts with 4” ribs. The recurves are scraped to about the same thickness, say 1/8” to what you appear to have as a starting point so I can’t say if thinner will help you without it getting a floppy sound for lack of a better description. Good luck in trying to go any thinner with the size of body you’re working with. I would not be as as adventurous to go thinner myself.

I do a lot of area tuning. It doesn't take very much stock off at all. Just use scrapers. I tap the top, and back; lightly, and find high spots. Scrape the highest spot, lightly, and test again Keep doing it until it is all pretty even. If you didn't do this on the inside on your braces, they might be high over them. Yours don't look like they will be too bad. I've never used cross braces, my arching is already made with diagonal arches. I've only used parallel braces on arch tops, and ladder braces on other guitars. I don't know anything about them. I would guess on an archtop they magnify the arching that is already there.

The highest tapping areas, and your most work, will probably be around the edge; but high spots can be anywhere.. Don't tap over the linings; go a ways inside of the linings. The same with the blocks. Don't spend a lot of time in one spot. Tap to see if there is a ridge of highs, or just a peak in on spot. After you've done some, since yours is set up; you can play and see if some of the notes are more clear.

If it isn't doing anything, then check again all over, and see if there is something that you missed. If it is all even, I guess that is how it sounds.

If it sounds better, then check all over again, and see if there is something that you missed. It could get even better. You should be only taking little shavings.

There is at least one guy who does cellos, and checks each note. If a note is weak, he finds where a glob of blue tack makes the note better. Then after checking to see if it makes any note noticeably worse; he thins it there.

I have not experience with that. I do know that tuning the belly for a tiny use sized Baroque guitar, free plate; I can hold it in different places all around the edge, and tap out chromatic notes. It isn't glued on, but is sounds promising.

One last thing. I'm thinking that after sealing, you should go over it again. Then re-seal the scraped parts and check it. Some parts may soak in more sealer, and change the stiffness some. I only did this on the last viola I did.

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