How do properly repaired cracks in the body of an acoustic guitar affect sound (if at all)?

Question

A guitar I'm looking to buy (acoustic flamenco guitar, Alhambra) has a crack in the top (is that the correct term for the "audience-facing wooden panel"?), running closely alongside the neck all the way from the hole to the edge where the neck leaves the body. The crack has been repaired by a professional.

I assume that the crack is properly repaired, so that there is no risk for the crack reopening, growing or causing further problems (I understand that cracks running perpendicular to the neck are more dangerous in that respect, since they are constantly under stress due to string tension). But is it likely that the sound of the guitar is affected by a crack such as the one described? I am particularly worried since the crack connects with the sound hole.

(EDIT: I realize the question in the title is more generally posed than the one in the post. However, a more general answer, discussing different body crack types, would also be very welcome)

Answer 1

The sound will absolutely be affected; how much is hard to say. You should definitely play it and see how it sounds.

The soundboard of an acoustic guitar is designed to amplify the vibration of the strings, and if it's not one piece the pieces are laid together carefully to help prevent dampening of the vibration. It's generally best if the grain of the wood is all one direction, for example. A crack interrupts the vibration and stops it from transmitting.

If repaired, some vibration continues to be transmitted across the crack, but not as much. It's similar to cutting a wire and then soldering it back together — electricity can still pass through, but the soldered point is higher resistance than it was before. The extreme case would be a crack that completely splits the soundboard in half, which would have a major negative effect (similar to not soldering the wire together properly).

Your crack, being on the upper portion only, may not be as significant, though certainly more so than (for example) a small split in the middle of the wood. I think it's probably also good that the crack is parallel to the neck, since I would expect most of the vibration to also be parallel to the neck at that point.

Answer 2

My father has a 1979 Ramirez guitar that got damaged. He took it to a local luthier who repaired it. The guitar still sounds wonderful. I would imaging that your guitar should retain the sound that it had before. If you like how the guitar sounds then you should buy it.