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I'm building my first two guitars (well. in truth 2 and 3 but I don't count my first atempt as a guitar). I've closed the box on both of them.
The first has a low grade spruce top I, in my inexperience, bought off ebay.
The second has a really niece German spruce top.
I've been holding the guitars by the neck block area and tapping around comparing the sounds on both.
Comparing the 2, the first has a lower fundamental note with indistinct overtones. The second sounds much higher and as you tap various places the overtones are more obvious.
I havent got as far as using a computor to analyis the frequencies (that might come when I buy Trevor's book).
But, based on this information, and all other things (bridge material, weight etc.) being equal, is it possible to say what the guitars might sound like when finished? Or, perhaps easier, which you might expect to be a better guitar?

Am I correct in thinking this: the bracing on the second was not as stiff as on the first, but being a better quality wood, the top is stiffer and hence the higher frequency tap tone?

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We are all in the gutter but some of us are looking at guitars.

All you I would say on the basis of the information you've given is that the second top, as installed, may have a higher stiffness to weight ratio. It could be the bracing, it could be the top, it's probably some of both. That, in itself, has very little to do with how the guitar sounds, or how good it is. That's a function of how all the elements work together: it's more a matter of relationships than absolute values. Yes, you do want to avoid having strong low-order resonances exactly on scale tones, but there's a lot of leeway there, and 'want to avoid' is not the same thing as 'must not have'. It's all about balance, and there's no way to know that from the information we have.

It's really hard to say anything Joe, given what you've told us.

I just boxed up a guitar which sounded really dull to the tap. Fortunately, I knew immediately what the problem was: porous back wood. I'd come across this before. Basically, if you have enough pores of a large enough size, the back doesn't form a seal and air pumps through all the holes. The problem goes away, of course, as soon as you fill the pores/apply the finish. I suspect not many people come across this issue because of sanding wood to thickness (I plane mine). The sanding dust is sufficient to stop the air flow. I logged all the taps, so will put them up at some stage.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks for replies.
I quess I'm just trying to understand or gain the experience of being able to tap a guitar and say "ah, this is a good one".

I'm going to go down the more analytical approach but, as I've said before, the most frustrating part of learning this craft in isolation is understanding the sensery experience of making- how wood feels. flexes, sounds etc.

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We are all in the gutter but some of us are looking at guitars.

The smart bet is that they will sound like guitars.

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http://www.CostaGuitars.com
PMoMC