Adjusting the graduation with the guitar strung up

[Jeff Chumley]

I just strung up an archtop in the white that I have been working on off and on for a few years. I know I can play it and remove wood from the recurve to adjust the sound but I'm not sure what to listen for. Currently it is quite loud and a little brash with a lot of sustain. It sounds Piano-like in a way. I am assuming this is a tight sound and thinning the recurve will smooth it out. I am comparing it to an archtop I built in Dale Unger's class which is a little less loud an quite a lot darker and smoother sounding. Unfortunately I can't go back in time and compare the two of them when they were both unfinished. It could be that the first one was brighter at first and smoothed out over time.

I know without having it in hand it is really not possible to judge but is there anyone who wants to judge anyway? Does this sound like a description of a tight top?

Jeff

[Michael Lewis]

Jeff, they are always brighter when freshly new.

How thick are your plates (center and rim)? What sort of arching did you use? Bracing? What wood is the top? the back? the neck? String brake angle over the bridge? It all inter-relates. There are a jillion more questions that hold a bearing on your sound, but these are some of the bigger ones.

Before you go removing any wood I suggest you think it over carefully first. The guitar may change right before your eyes.

[Jeff Chumley]

Michael,

Thanks for responding. I guess I did leave out a lot of important info didn't I?

Size and general shape: It is a 17" guitar that is very similar in size and shape to a Benedetto. Even though I drew up the design and bent the sides prior to taking the class, the design I came up with looks a lot like a Benedetto. The differences are subtle.

Top : Sitka spruce - about 1/4 down the center seam tapering to about 3/16" at about 2" from the center seam on either side. Recurve currently is kind of shallow at about 1/32" deep (5/32" thick in the channel). The nature of the arching is based on Benedetto. The arch is more Stradivarius Than Steiner if you know what I mean. The slope down from the top to the edge is not sudden and "blister" like. The arch is about 7/8" at it's highest point on both top and back.

The x bracing is about 9'16" tall in the center and 5/16" wide.

Back and sides: Curly big leaf maple - back is about 3/16: with no taper. Recurve is a little more pronounced than the top.
Neck is Hard curly maple.

The arching and bracing are very similar between the two guitars but the Unger class guitar top is closer to 3/16" in the middle and doesn't taper much . Also it has European spruce and maple.

Break angle I'll have to measure later but it is essentially the same on both guitars. Bridge is about 1" high and neck angle is 4 1/2 deg.

The bridges are very similar. I made the new one based on the dimensions of the other. I haven't weighed them but they are probably very close.

I'm thinking now that New strings on a newly built, unfinished guitar should sound a bit bright and after playing it for an hour last night, I went back to the other guitar and it sounded dull to me. I'm not in a rush because I can't spray finish until the humidity drops here in the DC area. I have to spray outside you see.

Here are the two guitars for comparison.

[Michael Lewis]

I like the lines of your new tail piece. Your arching sounds about right but I think you might want to thin the recurve of the back if it is 3/16". The flexibility of the back is what gives the fuller and bassier response.

Take my input with a grain of salt as I am not tuned in to Benedetto 'system' of structure. I have spent a lot of time with the D'Angelico 'system' (1/4" in the centers of the plates, more graduation on the back than the top, etc.).

Put a new set of strings on your old guitar for a comparison.

[Jeff Chumley]

Well Michael, I'd say you pretty much nailed it. I scraped quite a bit off the back recurve ( a bit at a time) and the sound is much better. It doesn't sound quite as loud overall but the low end is much rounder sounding. I've still got a bit more to remove but I think I'm almost there.

Thanks

[dave mattey]

Hello - I was searching for a thread like this as I am in the same position with a new build strung up and checking the sound while scraping the recurve. Like others I don't really know what I am trying to hear! The sound is bright and woody, but I'd like to hear some more deeper bass. Deepening the back recurve has made a difference though, and the resonance is coming through - but how far to go?

The guitar is a 17" Benedetto style, pretty much following the book. Spruce top, parallel bracing, plate thickness close to but maybe (unintentionally) just slightly thinner that the recommended spec. Back plate is flamed maple, 5mm thick, pretty uniform.

I am using a strong light to monitor how the recurve is thinning out and can measure the thickness near the f holes and I think the back plate is around 3.5mm now at its thinnest. As I said, when do you stop?!

A couple of other questions - should the recurve be continued across the neck and tail blocks? Right now it fades out completely over the neck block and shallows near the tail block.

Should the tap tope be similar front and back? The front is deeper sounding than the back, which is quite bright still.

How much might the neck weight affect the resonance of the body? The neck profile is rather 'vintage' at the the moment (by choice), might taking some mass off by shallowing it change the bass response?

The sound though changes to my ear almost hourly - I have no other archtop to compare it to easily, and it is (and should be I guess) so different to my flattops. I went round my music store last week and recorded a whole bunch of classic arch tops.... I think there is a little way to go still!

Thanks for any advice

dave

[Michael Lewis]

The thinner the plates the more they respond to low frequencies, and it can go all the way to "muddy" sounding. Your own sensibilities will have to direct you through this process. You need stiffness or you will have no power, but too stiff gives bright, shrill, quite. You are in the "ball park", now you need to find where you specifically want to be. No one can tell you what sound YOU prefer, any more than they can tell you what food to like. You can always remove more material, but can't put it back on.

Do not continue the recurve across the neck block. Some do but it doesn't look good and can lead to structural issues. Do the recurve across the tail block but not as deep as around the sides, so the thickness in that area supports the center seam and will resist collapsing. There is a lot of compression force in those block areas.

[dave mattey]

Thanks for the advice - I think I am there, no more scraping!