Jallawalla Posted January 17, 2012 Posted January 17, 2012 From my reading on this forum I have heard that gibson acoustic flat tops are arched/radiused. I just bought a southern jumbo second hand (and love it!), but now I'm thinking that maybe the top is a bit too arched. No idea how it was stored (humidity etc.). Photos are of the top, but the back is arched about the same amount. To my mind there is a slight dip from neck joint toward soundhole, but not sure if it's by a meaningful amount. Any views?...and thanks in advance for all input/comments. 12 inch straight edge from fretboard
BigKahune Posted January 17, 2012 Posted January 17, 2012 . It seems to have a bit more of a belly than my 200. Is it now acclimated to a proper temp/humidity environment? What gauge strings? The action - is it okay? High? Or was the action adjusted recently to compensate the belly? .
EuroAussie Posted January 17, 2012 Posted January 17, 2012 Hmm, interesting, it does seem to be a bit arched at the belly. Should be relativelly straight or with a very slight arch at the belly, more significant one at the back. Sort of looks like an overhumidified guitarm, have you been humidifying it ... or keeping it in the bathroom by any chance ?
slimt Posted January 17, 2012 Posted January 17, 2012 I think the top will always be arched when there is alot of tension from the strings.. the neck is tilted back a certain degree as well. the spruce braces have a certain amount of flex.. Just about all that Ive owned have been the same way.. thats why its important to keep guitars humidfied . to prevent sound hole sinkage,and braces from cracking... once the braces dry out completely it is hard to regain moisture .. I do believe they have a slight arch when there built in the Factory.. correct me if Im wrong..
Jeremy Morton Posted January 17, 2012 Posted January 17, 2012 . It seems to have a bit more of a belly than my 200. Is it now acclimated to a proper temp/humidity environment? What gauge strings? The action - is it okay? High? Or was the action adjusted recently to compensate the belly? . It looks good to me. if the guitar was over hydrated the ruler would be sitting on the bridge and would be lifted off the frets at the end of the fret board. JM
larryp58 Posted January 17, 2012 Posted January 17, 2012 It does seem to have more radius than mine, but as said previously, has it acclamated to the present temperatureand humidity? Seems a lot of radius, but nothing really to worry about.Just keep an eye on it or let a luthier go over it to make sure.
BigKahune Posted January 17, 2012 Posted January 17, 2012 .... I do believe they have a slight arch when there built in the Factory.. correct me if Im wrong.. Right Slim, as the OP noted in his post. If the action is good and the bulge is stable, should be okay. If the saddle is getting low to compensate the action, not good. I bow to Jeremy. .
Jeremy Morton Posted January 17, 2012 Posted January 17, 2012 It looks good to me. if the guitar was over hydrated the ruler would be sitting on the bridge and would be lifted off the frets at the end of the fret board. JM Coreect! The guitars are built with a radius on both the top and the back at the factory. The pictures show what appears to be a healthy radius. Flat would be dehydrated. If the action was really high and the saddle low/ Bridge high would be a sign of over humidification. JM
Del Nilppeznaf Posted January 17, 2012 Posted January 17, 2012 Jallawalla, looks good to me. My new direct from factory Hummingbird has similar amount of belly but i'm no expert, Jeremy Morton says its good... i'd take his word
bobouz Posted January 17, 2012 Posted January 17, 2012 Assuming the fretboard action is where you want it, your saddle height looks very good. I wouldn't worry about it one bit. Fwiw, every J45ish Gibson I've owned has had a belly, some more than others, but it's a non-issue if the guitar is structurally sound & everything lines up from a playability standpoint.
Danner Posted January 17, 2012 Posted January 17, 2012 I just checked my TVSJ, and it has the same bulge as yours. I keep mine at 70 degrees and 50% RH too. I am not worried about mine at all.
dhanners623 Posted January 17, 2012 Posted January 17, 2012 Looks perfectly fine to me and looks much like my '98 J-45, which has great action. You have to keep in mind the top is "loaded," meaning the braces have a slight curvature or radius, giving the soundboard the shape you see in your photos. To quote Norman Blake: "Never trust a guitar if it doesn't have a belly." He would know.
j45nick Posted January 17, 2012 Posted January 17, 2012 I just pulled out the plans for the J-45. The designed transverse back arch is just about 1/4" (just under 6.5mm) roughly at the bridge. Transverse top camber at the back of the bridge (rim to rim) is about 2.5mm(just over 3/32"). Longitudinal top arch on centerline starts at 0 at the end of the fretboard, peaks at just over 1/8" (about 3mm) about 2" (50mm) behind the bridge. In practice, my 1948 J-45 has a shade more longitudinal top arch. What I see in your photos looks reasonably close to this. Remember, it's wood. It moves with the humidity. I see nothing to be alarmed about. A Gibson "flat top" ain't flat, either top or bottom. The bottom arch is just over twice that of the top, both longitudinally and transversely. Longitudinal and transverse camber (arch) greatly add to the stiffness of the body. Bending and gluing the flat top and flat back to the arched braces (they are all arched to some degree) pre-stresses the top and back, making a very effective girder when they are glued to the rims. On my guitar, a 12" (300mm) steel rule resting on edge on centerline atop the frets from 13 on up just about kisses the top of the bridge (not the top of the saddle). This seems just about perfect to me, in any case. Anyone who loves these guitars should have these plans. You can get them from Stew Mac, and a few other places. And, no, I don't get a royalty off them.
Jallawalla Posted January 17, 2012 Author Posted January 17, 2012 Wow what a fantastic community here! Thanks so much for the input. I'm going to try to answer all the questions if I can. Is it now acclimated to a proper temp/humidity environment? No idea - I got it 2 days ago. I have never had a hygrometer (didn't know about them til I got this fancy guitar) What gauge strings? I've just put 11s on there The action - is it okay? High? Or was the action adjusted recently to compensate the belly? No idea if it's been moved. I'd like it a touch lower, but I'd describe it as 'good' (pretty low) It looks good to me. if the guitar was over hydrated the ruler would be sitting on the bridge and would be lifted off the frets at the end of the fret board. That was my conclusion from that measurement, although you can't see it in the picture too well the ruler IS lifted off the frets at the end of the fret board, but only a little. And to all the other points. Thanks
Jallawalla Posted January 17, 2012 Author Posted January 17, 2012 Firstly, thanks for your thorough and well researched answer. Looking at your numbers and without measuring it I think I have somewhere near a 1/4" arch in the top. It was this amount of arch that was bothering me as it seemed a lot, although the fact that the neck was lined up very well with the bridge did reassure me quite a bit. I just pulled out the plans for the J-45. The designed transverse back arch is just about 1/4" (just under 6.5mm) roughly at the bridge. Transverse top camber at the back of the bridge (rim to rim) is about 2.5mm(just over 3/32"). Longitudinal top arch on centerline starts at 0 at the end of the fretboard, peaks at just over 1/8" (about 3mm) about 2" (50mm) behind the bridge. In practice, my 1948 J-45 has a shade more longitudinal top arch. What I see in your photos looks reasonably close to this. Remember, it's wood. It moves with the humidity. I see nothing to be alarmed about. A Gibson "flat top" ain't flat, either top or bottom. The bottom arch is just over twice that of the top, both longitudinally and transversely. Longitudinal and transverse camber (arch) greatly add to the stiffness of the body. Bending and gluing the flat top and flat back to the arched braces (they are all arched to some degree) pre-stresses the top and back, making a very effective girder when they are glued to the rims. On my guitar, a 12" (300mm) steel rule resting on edge on centerline atop the frets from 13 on up just about kisses the top of the bridge (not the top of the saddle). This seems just about perfect to me, in any case. Anyone who loves these guitars should have these plans. You can get them from Stew Mac, and a few other places. And, no, I don't get a royalty off them.
Jallawalla Posted January 17, 2012 Author Posted January 17, 2012 ...and one last thought that just occurred to me. The original gibson case it came in is very worn for only being a few years old. The black covering is lifting up all over the place. It's not really CSI, but I wonder if damp conditions did that to the case and the damp has let the arch come up just a little bit. I have read all over the place about this and it seems that if the humidity goes back down then the guitar will probably settle back down too.
Jeremy Morton Posted January 17, 2012 Posted January 17, 2012 The case did its job and protected the guitar! If you are not the original owner you will never know what the case and guitar have gone thru. If the guitar was exposed to high levels of humidity it would show signs of that. from the pictures it does not appear to have issues from high humidity. The arch on the top is natural.
j45nick Posted January 17, 2012 Posted January 17, 2012 ...and one last thought that just occurred to me. The original gibson case it came in is very worn for only being a few years old. The black covering is lifting up all over the place. It's not really CSI, but I wonder if damp conditions did that to the case and the damp has let the arch come up just a little bit. I have read all over the place about this and it seems that if the humidity goes back down then the guitar will probably settle back down too. If you don't have one, you should get a high-quality digital hygrometer to monitor humidity in the room where the guitar is kept. The humidity in the room may vary constantly unless it is climate-controlled, but keeping the guitar in a high-quality case flattens out the rate of change of humidity. There have been a fair number of discussions here about the appropriate humidity for your guitar, but you have to start out by understanding the environment the guitar lives in.
gijs Posted January 17, 2012 Posted January 17, 2012 Guys and ts specifically: stop worrying. It looks normal and Jeremy from Gibson confirms that. He knows his stuff!
pfox14 Posted January 18, 2012 Posted January 18, 2012 If the guitar has more top deflection than the normal radius then it could be caused by a thinner top being pulled up slightly by the string tension. This would also cause the bridge to dip slightly toward the soundhole. Looks like it does, but is NOT causing any problems with the action of the strings. I would leave it alone. Probably sounds really good with a thinner top anyway.
Jinder Posted January 18, 2012 Posted January 18, 2012 Looks absolutely fine to me. All of my Gibsons have had a slight parabolic arch in the top, they're designed that way as has been pointed out previously. The very slight forward inclination of the bridge is nowt to worry about. All of my belly-up bridges have had the same angle and the rectangular bridge on my AJ does too. The geometry of your guitar looks good, there is plenty of saddle showing and the action seems great, so play on and enjoy :-)
rar Posted October 9, 2012 Posted October 9, 2012 Looking at your numbers and without measuring it I think I have somewhere near a 1/4" arch in the top. It was this amount of arch that was bothering me as it seemed a lot, although the fact that the neck was lined up very well with the bridge did reassure me quite a bit. Well, let's see. The built-in top radius is 28 feet IIRC. The obvious similar triangles imply that the arch in inches is X where X/8 = (2/3)/28 (where 8 is half the width of the top in inches and 2/3 is the half the width of the top in feet) -- call it 0.2 in. Pretty close to what you're seeing. -- Bob R
bobby b Posted October 9, 2012 Posted October 9, 2012 Mine looks the same, it's normal.... ...... no worries... now just play it!!
drathbun Posted October 9, 2012 Posted October 9, 2012 Keep it looking just like that and you'll have a very happy guitar! :)
Dave F Posted October 9, 2012 Posted October 9, 2012 It looks good to me. if the guitar was over hydrated the ruler would be sitting on the bridge and would be lifted off the frets at the end of the fret board. JM I agree. I think the perfect setup is the top of the bridge (not the saddle) should be even with the frets. If anything, you look a hair low. I have a newer J200 and it bellied up over the summer and the bridge is higher than the frets which puts the action way higher than I prefer.
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