Cause of High Action Has Me Stumped

[bfisch4]

I have an acoustic that has developed some very high action at the 12th fret over the last year or so (the guitar is 15 years old). I checked the neck for bow, and it's solid and has an appropriate amount of relief. I checked the neck angle by placing a straight edge on the fret tops running the straight edge toward the bridge. It's sitting just above the bridge, so that's solid. The saddle is the same as before when the action was ok. What else would cause the action to become suddenly higher? Could it be too much of an upward warp of the top? If so, wouldn't I have also detected that when I ran the straight edge toward the bridge? I have extra light .10-.47 strings on it as well, so I would think the lesser tension wouldn't bow the top as much. Just curious to get your thoughts on what could be causing this high action.

[YamahaGuy]

Has there been a recent change in humidity? Do you humidify the guitar? Is it new to you? New to your home? You mention the guitar's age, but not how long you've owned it.

My guess is that is has severely dried out and needs to be rehydrated.

My guess is the prior owner had it in a more humid climate and that your climate is dry and that you do not humidify the guitar. And you've had it about a year.

[runamuck]

Originally Posted by YamahaGuy

Has there been a recent change in humidity? Do you humidify the guitar? Is it new to you? New to your home? You mention the guitar's age, but not how long you've owned it.

My guess is that is has severely dried out and needs to be rehydrated.

My guess is the prior owner had it in a more humid climate and that your climate is dry and that you do not humidify the guitar. And you've had it about a year.

If humidity is truly the cause, I'd guess just the opposite: that it's over-humidified. With low humidity, the top sinks making the action lower.

[John Arnold]

'High action' is not quantitative. If neck relief has not changed, then the straightedge measurement has. That suggests that the top may have bellied.
Is the neck heel tight against the body?

[Mandobart]

Do you have actual "before" measurements of relief, neck angle, saddle height, action? Do you really know none of these have changed?

Most of these changes aren't sudden, unless there's been a mishap, or you don't even try to maintain constant temperature/relative humidity, or you just changed strings, saddle, nut..... It's usually more like the frog in the saucepan slowly being raised to a boil.

[bfisch4]

Alright, here are some more details. This is a friend's guitar that he asked me to do a set up on. It sounds like he played the guitar for years with no issues. Stopped regularly playing the guitar for a couple of years and left it in the case under tension in a temperature controlled finished basement. About a year ago he takes the guitar out to start playing it again and notices uncomfortable action. I've measured the action at the 12th fret low E at 0.13 inch. and he prefers it around 3/32 inch at the 12th fret low E. The neck heel is tight against the body.

[Mandobart]

Well there you go. No way to know what (if anything) has actually changed. If it was my guitar and the relief was good and its not a bolt-on neck with shims and such I'd first make sure my nut slots were good, then sand the bottom of the saddle to get slightly more than the desired action at the 12th fret. Play for a couple months and see if I needed to sand any more.

[bfisch4]

Thank you all for your advise. There is a possibility that the basement it was stored in for a while was very humid and maybe high humidity caused the top to swell or belly up. I'll leave the guitar in a properly humidified room for a while and reassess. I agree that ultimately I'll probably need to take the saddle down a bit to achieve the action he wants regardless.

[redir]

Originally Posted by Mandobart

Do you have actual "before" measurements of relief, neck angle, saddle height, action? Do you really know none of these have changed?

Most of these changes aren't sudden, unless there's been a mishap, or you don't even try to maintain constant temperature/relative humidity, or you just changed strings, saddle, nut..... It's usually more like the frog in the saucepan slowly being raised to a boil.

Exactly, without a before measurement you have no idea. 'Before' the straight edge test would probably shown that the neck angle was set too far back and you had too much airspace over the bridge but the action was perfect. Now that the straight edge test is ideal the action is too high.

Guitars always want to fold up like a book where the book binding is right at the body joint. It could be folding up or as you mentioned the top could be bulging up. If you have enough saddle left then simply lower it to get the desired action assuming all else (relief, loose bracing and so on) is good.

If not then you may be facing a neck reset.

[Mr. Paul]

I will add that a few days at 42% did nothing to remedy the belly problem I had on a purchased guitar that was over humidified. I took it to a shop and after 24 hours at 27% rh there was a marked improvement.

[bfisch4]

Originally Posted by redir

Exactly, without a before measurement you have no idea. 'Before' the straight edge test would probably shown that the neck angle was set too far back and you had too much airspace over the bridge but the action was perfect. Now that the straight edge test is ideal the action is too high.

I hadn't thought about the possibility of the neck being set too far back when it was manufactured and settling in at the proper angle later. Very interesting, thank you.

[YamahaGuy]

Originally Posted by runamuck

If humidity is truly the cause, I'd guess just the opposite: that it's over-humidified. With low humidity, the top sinks making the action lower.

I got it twisted. Thanks for setting me straight.

[nikpearson]

Originally Posted by Mr. Paul

I will add that a few days at 42% did nothing to remedy the belly problem I had on a purchased guitar that was over humidified. I took it to a shop and after 24 hours at 27% rh there was a marked improvement.

27% RH is very low, and whilst it would certainly bring the moisture content of the guitar wood down more quickly, there is also the risk of cracks. 42% RH is still lower than most makers/factories use, but I’d be confident that if you’d given the instrument longer at this latter figure you”d have achieved the same result eventually.

I’d be interested to hear the opinions of more experienced builders than myself around humidifying and drying instruments.