What Is Bellying? The large area of the front of the guitar below the bridge is called the belly. On some guitars it may arch out a little bit from the pull of the strings. This is called "bellying" and is normal as long as it only does it a little bit. This is how the front of the guitar (soundboard) amplifies the string vibrations and makes the guitar sound good; however, if it arches out too much, it could indicate a problem like broken or loose braces. Other causes can be you are using too heavy a gauge of strings, you're tuning to too high of a pitch, or your guitar was not fitted with strong enough braces to begin with. This is usually a problem of steel string guitars but can happen to nylon string guitars as well.

If bellying becomes severe enough, the bridge will actually start to tilt towards the soundhole, the bellying will become very pronounced, and the playability of the guitar will be in jeopardy. It is a pretty big repair job if you need to get it fixed. Find a competent repairman.