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I got a 12-string Ibanez acoustic today with an initial complaint of high action. After some measurements I knew that the truss rod was loose, but that could not compensate for 2 mm of overhead in action. The bridge is app. 9 mm high, I think you can call it "by the book". The neck angle didn't seem right. No separation in the finish, no lifting as far as neck/heel/fingerboard tongue goes. Now the interesting bit.

There's all kinds of whackiness on the top around the soundhole. Putting a straight-edge parallel with the strings on each side of the soundhole shows me hills and valleys. It is most severe on the outer-most edges of the soundhole, and there's a big wrinkle on each side facing up towards strings. No cracking or signs of excessive dryness, I would expect a collapse would push the soundhole edges downward, but these curl upward instead. Could it be that the guitar already started suffering from the string pull while it was still "wet" and fresh waiting for a buyer?

What do you guys think? Action is high, relief is now okay, the neck angle falls at 1/3 of the bridge height without the saddle and the top is very bumpy on the sides.

I will get some pictures tomorrow, strangely today all of my battery-powered equipment is in bad need of fresh electrons.

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How old is this guitar? Ply top? Have you looked for loose or cracked braces?

I think it's a 2009 or 08, it has a flame maple top, sides and back also out of maple.

This is how it looks like when I lay a straigh-edge parallel to the strings. The other side is the same. The picture does not show it, but the soundhole has two raising points opposing each other, just like a rim of a plastic cup when you squish it lightly. As if it wants to get an oval shape, but it is still round of course. It has been sitting in my shop for three days, just to see if maybe humidity could stabilize it even further. I noticed a slight drop in action without touching anything on the guitar for the past two days, so maybe the top relaxed just a tiny bit? Still, the strings are a mile too high for comfortable playing.

I have no clue whether this is ply-top or not, the edge of the soundhole is finished, on the inside it shows a maple grain, but could be a simple two-side laminate too, no doubt.

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Fairly typical symptoms of 12-string disease.  The top is bellying up behind the bridge and is caving in between the bridge and the soundhole.  The bridge is rotating towards the soundhole, raising the action.  If your description of the neck angle was obtained with the strings off or slackened then it also has a neck angle rotation.  All of this is due to the string tension.  Like Greg said it would also be important to check for bracing failures.  I think you can assume that this thing has a ply top. 

How to fix it?  A Bridge Doctor will usually flatten the top and restore the correct rotation of the bridge.  They are cheap, and easy to install.  This is the best strategy to restore playability in a relatively cheap instrument.  Obviously, if you find another structural failure like an unglued brace you will want to restore that. 

If the geometry comes good but the action is still a bit too high, you will then have the option of shaving the saddle.  Neck reset is probably hard to justify in this relatively cheap guitar. 

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