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Why don't hollow body acoustic guitars crack? (lemmy.world)

submitted 1 month ago by tehfishman@lemmy.world to c/woodworking@lemmy.ca

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I'm hoping someone here can explain something that I haven't been able to find a satisfying answer to - why don't traditional acoustic guitars crack? I mean obviously sometimes they do, but it seems to me like that should happen all the time. For anyone unfamiliar, the front (top) and backs of wood acoustic guitars have their grain direction running parallel to the neck. And inside, there is bracing. That bracing runs perpendicular to the grain of the top, and the bracing is typically glued to the top. Gluing perpendicular grain is generally considered a huge problem when it's an item of furniture and it would be reasonable to expect an object constructed like that to tear itself apart in a few years as humidity fluctuations do their thing. But guitars usually don't do that and I don't understand why.

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[–] celeste@kbin.earth 10 points 1 month ago (1 children)

https://www.classicalguitardelcamp.com/viewtopic.php?t=132051

I don't know, but here's a conversation between guitar fans about it. The wood has to be treated carefully or it will crack, I guess.

[–] tehfishman@lemmy.world 6 points 1 month ago

There's some interesting information in here for sure. Some speculation about intentional allowances for some warping to occur, and information about how some tops are basically 3-ply plywood which is a bit more stable.

[–] bluGill@fedia.io 4 points 1 month ago

Every music store sells humidifiers because it is well known that if you don't keep your acoustic wood instruments (not just guitars, violins, harps, pianos...) at a very consistent humidity year round they will crack. If you go looking for antique musical instruments you will see a lot of them with cracks. The ones that are not cracked are the ones where the owners have cared about humidity and temperature.

[–] notittypicsplz@lemmy.world 2 points 1 month ago (1 children)

Making guitar soundboards is a lengthy task. First, trees with very straight grain are chosen this means very little twist to the tree. I know of a guy not far from where i live who goes out to the block where the logging is happening and he will use an ax to split the wood and see how straight it is. Then those trees are brought back and quarter sawn, making wedge shaped strips of the tree. Each piece is carefully inspected and pieces with defects such as knots are discarded.

The pieces then get bookmatched and hung to dry, and while wood generally takes 1 year per inch of thickness these actually are hung by clothespins for 2 years, if I remember quickly. These are then packaged and shipped after another close inspection.

I also assume that wherever the soundboards are being used to build guitars, that they are given time to balance the humidity of the new room.

Another factor is that the wood is very thin, and therefore there will be much less wood movement than there would be in a 2x4. Wood veneer is known for being stable for example. With such thin material you don't end up with one side being dryer than the other, so you don't have excess shrinkage one side over the other.

[–] the_mighty_kracken@lemmy.world 1 points 1 month ago

Also, a fine acoustic guitar will have a very slight arch in the back and front. (About 1/16 - 1/8") That means that if there is some movement in the wood because of humidity, that movement tends to increase or decrease the arch, rather than splitting the wood apart.

[–] not3ottersinacoat@lemmy.ca 1 points 1 month ago

Because they're made in wells.