Official Luthiers Forum!

Hello, I'm new to the forum & thanks to Lance for approving. English is not my first language, so I hope you will understand if anything is not so clear.

I have been playing the electric guitar for some time and recently my friend get me interested in acoustics. I have been watching videos on youtube about guitar building and repair and I am fascinate with acoustics guitars.

I also bought a beginner acoustic guitar, about 5 months now. I bought brand new. I just noticed that the guitar top is not flat. I can feel the bulge with my hand but better if I show you photos

look from side, I press ruler flat towards the neck


look from bottom to neck, ruler balance in the middle


Because it is not old guitar, I am surprised why the top is like that. The strings have not been changed before and are original from factory.

Can anyone please explain if this is normal for new guitars? If it is not normal, what are the likely reasons for this phenomenon? Is it defective?

Thank you

It’s normal.

what your are seeing is the top pulling from lack of RH control. This time of year things get dry so get a sound hole humidifier if the guitar gets too dry the top will split.
flat tops are not flat by the way this is a reference to the arch top comparison

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Lefestin, welcome to the forum. Since English is not your native language, I will explain things to you a bit more simply.

Acoustic guitars are often called "flattops" even though the tops are not flat. The guitar is made with a radius (curved surface) in the top and back. Different brands and different builders use different radii for their guitars, but all guitars have them.

In addition to the built-in radius, the top will also develop a bit of extra curve when string tension is added. This is called the "load" and is normal unless it becomes excessive. 2-3 degrees of bridge rotation is considered normal.

Acoustic guitars need to be kept in an environment where the relative humidity is withing a safe range, generally 45% to 55%. Allowing the guitar to become excessively dry will cause changes to the top curvature, and possibly other bad things such as cracks, bridges coming looses, and sharp fret ends. A good way to help prevent drying is to use Humidi-paks in the guitar case, if you can get them where you live. A small plastic box with holes drilled and a wet sponge inside is better than nothing.

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It will probably be alright.

But dryness will not cause a bulge. The top will flatten as it gets too dry and that's what causes cracks and why it's good to build a dome into the top from the beginning.

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Hutch

Get the heck off the couch and go build a guitar!!!!

Welcome to the group!
Your English is very good.....

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Measure Twice,

Karl Borum

that looks awfully like my '86 Taylor K20 looks like, and that was caused by humidity deforming the top and requiring (IIRC) 3 neck resets over the years (actually that might only be 2, after one of them I complained about the ski ramp effect over the top and actually had to tell them to put a damned wedge underneath the FB extension and sent it back for them to do so...sheesh, here I was in college and did have some woodworking experience but not much, and I'm telling them how to solve the issue :facepalm:)

anyway, from my experience a dry guitar will have a low action, and a wet guitar will have a high action...if your action is OK then perhaps the guitar was built that way

Yes, the simple answer to the original post is that that amount of arch is quite normal for the top of an acoustic guitar.

As other people have mentioned the humidity in the air can cause that arch to change from day to day. This is also OK, as long as it does not become too extreme. It happens because wood naturally absorbs water from moist air and swells, or looses moisture into dry air and shrinks. If you have ever noticed the wood windows or doors or drawers in your house getting jammed tight in wet weather it is the same thing. Guitar soundboards experience a lot of humidity flux because they have a huge surface area exposed to the air, relative to their mass.