Should the Top of an Acoustic Guitar Be Flat?

acoustic guitar | Sandy Music Lab

If you’ve seen a new acoustic guitar, you probably noticed a flat top underneath the strings. When looking at a guitar with a bulge on the face of it, especially an older guitar, it’s easy to start panicking that the guitar is ruined. Are acoustic guitars meant to have flat tops, or can they ever be curved?

The top of a standard steel-string acoustic guitar is flat or mostly flat when first purchased. However, most guitars will eventually buckle under the string tension between the neck and the bridge. Luckily, if your old acoustic guitar’s top begins to warp, a luthier will be able to fix it.

This article will explain why the top of acoustic guitars can warp from flat to curvy as time goes on. It will also explain what to do when the top develops too much of a bulge or even if the face of the guitar sinks.

Why Do Acoustic Guitars Warp?

Most acoustic guitars are what are known as “flat top” guitars, which have (you guessed it) a flat top. However, quality acoustics will eventually warp by design.

Why is this? The answer lies in the way acoustics project their sound.

How Acoustics Are Constructed

Acoustic guitars work by vibrating their strings over a soundboard and hollow body to project noise. They’re built with a hollow chamber and a bridge to support the strings. The bridge is what pulls the strings up off the top and keeps the tension high.

There is a fundamental difference in the way that low-quality and high-quality guitars are manufactured. Because low-quality guitars are mass-produced, they use more rudimentary techniques and materials and cheaper shipping methods. Low-end guitars, therefore, actually have thicker top wood than high-end ones, which have thinner wood to create a richer sound.

Even an expensive guitar will eventually warp. In fact, because the faces of expensive guitars are often made with thinner, more delicate wood than cheap ones, they will likely warp sooner and more drastically.

This may look alarming, but you shouldn’t let it discourage you from buying a high-quality acoustic. The thinner wood is actually desirable since thicker wood can absorb vibrations and reduce sound.  

In some cases, warped guitar tops can enhance the sound of an acoustic. Read on to help identify if this is the case with your guitar.

Bulging Guitar Tops

Most well-made guitars will eventually develop a bulge somewhere around the bridge. This is because the tension of the strings along the flat top is constantly pulling at the bridge.

This isn’t necessarily a reason to replace or throw out your vintage guitar! Sometimes a warped guitar top will positively affect the sound. Since acoustics project their guitars out of their hollow chambers, any alteration to the materials will affect the noise they produce.  

A bulge will give the chamber more space for the vibrations to resonate through, making the sound more complex and rich.

Still, guitar tops are made of wood, not rubber, and enough pressure on the face will eventually cause it to crack. A crack in the guitar’s face will take all the power out of its sound and is very difficult to repair. That’s why it’s important to keep an eye on a bulging guitar top.

Sunken Guitar Tops

If you see not a bulge in the face of your guitar but a dip, then likely the issue is that the guitar hasn’t been humidified properly.

Wood shrinks and expands with environmental factors like heat and humidity. If you live in an area with low humidity, like Colorado or Arizona, you may need to take extra steps to keep your guitar top from shrinking.  

Shrinking wood will cause the face of your guitar to “belly” or sink. This won’t have any positive effects on the guitar but can instead make the neck appear to be warped and lower the action so much that the strings rattle. If the guitar is left to dry out for long enough, the face could crack and permanently damage it.

Luckily, you can fix this by simply starting to regularly use a humidifier on the guitar. The D’Addario Humidipak comes in three- and twelve-packs and maintains a humidity level of 45% – 50% in its instrument case no matter where you are. Keeping your guitar in proper humidity levels will go a long way to making sure it lasts a long time.

Use the humidifier regularly until you see the face start to even itself out. This may take several weeks but will be worth it.

What To Do With Bulging Guitars

Sunken guitar tops may be relatively easy to fix, but how do you fix a guitar top that’s bulging to the point of cracking? It may be tempting to try and fix the problem yourself with clamps and YouTube tutorials.

Unfortunately, this is not a problem most guitarists will be able to remedy themselves. Acoustic guitars’ musicality depends on how they are built, and this crucial piece of wood is quite thin even on cheap acoustics. If you break the piece of top wood while trying to flatten it out, you may as well kiss your guitar goodbye. 

Your best bet is to take your guitar to a luthier, someone who works with guitars for a living, as soon as a bulge on your guitar becomes noticeable. If you are taking guitar lessons from a professional, you can get your teacher’s opinion as well. The luthier could advise you against fixing the bulge if it’s minor. They may also tell you that cracking on the guitar is imminent and that you need to fix the problem immediately.

In any case, consulting an expert will give you peace of mind about your instrument. A skilled luthier will also be able to fix an overly-warped guitar without issue.

Archtop Guitars

While most acoustics are flat top guitars, there is a style that has a curved top built-in. These are called archtop guitars and are popular with jazz and blues players for their clear tone.

What Are Archtops?

Archtops are guitars with curved tops and backs instead of the flat ones on most modern acoustics. They typically have symmetrical f-holes on either side of the strings, like a violin, and have a very classic look. They can also be made semi-electric with pickups.

If you have an archtop, don’t be concerned about your guitar not having a flat face! These guitars naturally sound different from flat top guitars, with a cleaner, more “twangy” sound.

Archtops have the potential to warp as well, although their arched bodies tend to reinforce their shape against the strings’ tension. Just like with a flat-top guitar, that is not an issue you should attempt to fix yourself. It’s even more difficult to adjust the bulge on archtops since you are not attempting to adjust it to a flat top but the radius that it was before.

Final Thoughts

The tops of most acoustic guitars are flat, though some guitars are built with an archtop built-in. Most guitars will inevitably warp and gain a bulge on their faces due to the tension of the strings. A warped face can enhance the sound of your guitar, but it will also eventually lead to cracks in the wood, rendering it unplayable.

If you suspect your guitar is getting too profound of a bulge, take it to a luthier to get a second opinion. But know that bulging acoustics are perfectly normal and not the result of a lack of care on your part.

David Sandy

Hey there! My name is David Sandy and I'm the founder of Sandy Music Lab. I've been playing guitar for several years now and created this site to be able to share and explore music with others. Check out my recommended guitar gear!

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