Humidity and Curved Top, String Action

[PeteyPower16]

Hi All,

I recently purchased a Taylor GS mini two months ago. I have inspected the setup according to Taylor specs, including neck angle (correct to top of bridge), relief (correct/minimal), and yet my action is about 2/64 higher than Taylor specs.

Today, I noticed that the spruce top of my guitar is curving upward (please see photos below). On the guitar top, there is almost a centimeter of height difference between the bridge and the edges of the guitar. We have had a month with humidity in the 50-60% range. I am assuming that this rising of the bridge is responsible for my high action.

What are your thoughts on the following?

1. Is this amount of expansion/bridge elevation normal for the humidity levels we have had? Is this warping, or merely temporary expansion?

2. Could this be a construction issue, or would the soundboard have been flat when constructed?

3. Is my guitar in danger structurally/permanent damage? Any actions I should take to resolve the issue? Or just wait until the fall?

4. How much can I expect my action to go down as the humidity goes down this fall?

Thank you for your input!

Photos:
IMG_1585 by Peter Johnson, on Flickr
IMG_1584 by Peter Johnson, on Flickr
IMG_1586 by Peter Johnson, on Flickr
IMG_1587 by Peter Johnson, on Flickr

[LeDave]

I just the same test on my Fender after seeing this post. The center isn't flat all the way as like yours, however it's not as bad as yours.

Edit: oh! Welcome to the forum. I'm new here myself as well. Hopefully both our guitars will be fine. Not sure if it's natural for the guitars to do that curve or not.

[pagedr]

Acoustic tops aren't perfectly flat, that amount of curvature looks pretty normal. At those humidity levels I wouldn't expect any guitar to starting bellying, or for any structural damage to take place. If it were to get up to 75%-80%+ and remain there for a few weeks then that could present some issues, but 50%-60% isn't that high. All this to say, your guitar is likely as it came from the factory and it doesn't appear there were any construction issues with the top of your guitar. As for the action, if it is still high after setting proper neck relief and ensuring a good neck angle, then the saddle needs to be sanded down to get the action where you want it.

[KevinH]

I just checked 5 of my guitars and they all have about 1/2cm or so of "bow" as you measured it. I agree that 60% RH shouldn't cause much problem. There are AGF members that live in 70% RH (inside) w/o problems. It sounds like you have good relief and neck angle. You might also check the string height at the nut. If that's reasonable, it's not hard to sand the saddle. Just go slow and make sure you keep it perpendicular to the sanding surface. There are lots of videos online, as well as instructions here in the forums.

[Dbone]

Originally Posted by PeteyPower16

Hi All,

I recently purchased a Taylor GS mini two months ago. I have inspected the setup according to Taylor specs, including neck angle (correct to top of bridge), relief (correct/minimal), and yet my action is about 2/64 higher than Taylor specs.

Today, I noticed that the spruce top of my guitar is curving upward (please see photos below). On the guitar top, there is almost a centimeter of height difference between the bridge and the edges of the guitar. We have had a month with humidity in the 50-60% range. I am assuming that this rising of the bridge is responsible for my high action.

What are your thoughts on the following?

1. Is this amount of expansion/bridge elevation normal for the humidity levels we have had? Is this warping, or merely temporary expansion?

2. Could this be a construction issue, or would the soundboard have been flat when constructed?

3. Is my guitar in danger structurally/permanent damage? Any actions I should take to resolve the issue? Or just wait until the fall?

4. How much can I expect my action to go down as the humidity goes down this fall?

Thank you for your input!

Photos:
IMG_1585 by Peter Johnson, on Flickr
IMG_1584 by Peter Johnson, on Flickr
IMG_1586 by Peter Johnson, on Flickr
IMG_1587 by Peter Johnson, on Flickr

Completely normal. That is the exact profile you want with approx 1/4 on each side I believe. Not having that profile left to right is where it is problematic (dipping etc). Yer good.

[Wade Hampton]

Dbone is exactly right: this is a normal, intentional part of the guitar's design. By fashioning a slight dome into the top with the use of a curvature in the part of the top bracing that gets glued to the spruce top, what that does is both strengthen the top while also increasing its projective characteristics.

So that bowing makes the top stronger and more efficient in terms of sending the sound out.

The idea of the slightly domed top created by the bracing for flattop guitars is credited to a pair of Swedish bachelor brothers named Carl and August Larson, who emigrated to Chicago from Sweden and were prolific guitar and mandolin builders there during the 1920's, 30's and early 40's. Most modern acoustic guitar manufacturers since have incorporated the idea into their own designs, some more obviously than others.

Short version: it's a good thing, not a flaw.


whm

[LeDave]

An abundant of information from replies to this thread, as usual and always on almost every thread. Glad to know about this curvature!

[UncleJesse]

Norman Blake once said "Never trust a guitar if it doesn't have a belly".

[mercy]

Thats the way guitars are built now days. They have a little curve in the top.

[Earl49]

A "flat top" guitar does not have a truly flat top. Yours looks about right. The arch adds strength. It can increase with high humidity and sink with low RH. Sorry for repeating much of what has already been said - I posted first and then read through the thread. Welcome Petey!

[Pender]

My Baby Taylor has the same bowing and this guitar is a wonderful little thing. No worries

[ljguitar]

Originally Posted by Earl49

A "flat top" guitar does not have a truly flat top. Yours looks about right. The arch adds strength. It can increase with high humidity and sink with low RH. Sorry for repeating much of what has already been said - I posted first and then read through the thread. Welcome Petey!

Hi Earl

I called James Olson and had a 10 minute conversation about this topic because this topic emerges here in the forum with regularity.

According to James…his flat tops are built truly flat. My Olson Dreadnought is 27 yrs old. The string tension still lifts the top up between the bridge & tail.

I have two other handbuilts one of which was built with a cambered top and back, which at 15 years of age shows similar lift to the Olson (27 yrs old).

I agree the original poster's pic looks normal/fine.