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Hi, Im doing a science fair project on how the bracing on the top of the guitar affects the sound, so if any one has any advise on how to do bracing, or what you think and why a certian bracing style is better then the other.

Thanks

Hi, Cameron. I'm not the one to answer your question. It's a VERY complicated field of experimentation and discussion. But several bracing patterns have become fairly standard because they work so well. I am responding to keep your inquiry active in the hope that experienced builders will chime in and give you enough general information to complete your science fair project. Good on ya' for doing this project. I am always impressed by inquisitive, bright students who ask good questions. Straight ahead on your project, and best of luck to you.
Patrick

I have very little personal experience besides trying to learn myself but I think you should look at the vibrational modes of guitar tops & at what frequencies they occur then look at how different brace arrangements will help or hinder those modes. I no longer have it, but I think Somogyi's book did a good job of explaining this.

Kevin Looker

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I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Cameron,
As noted above, this can be a very complicated subject. There's a wealth of information buried here in forum pages. I did a quick search and pulled up a few threads you might want to follow:

search.php?keywords=modes+%2Bbracing&terms=all&author=&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search

There are probably several thousand more as well. Just start digging and you'll find them.

If your budget can't handle Ervin Somogyi's books, I've found Roger Siminoff's "The Luthier's Handbook," and "Art of Tap Tuning" to be pretty helpful. They offer concise information and are available on Amazon.com at fairly reasonable prices. You never know what your local library system might have, so I'd definitely recommend checking their catalog as well. In fact, that would be my first stop.

Good luck with your project!

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George :-)

As in any scientific investigation it is important to ask a question that you have a reasonable chance of answering. I believe your subject is too broad and will be difficult to deal with. Perhaps you could limit your investigation to the two most common bracing patterns for steel-string guitars, X bracing and ladder bracing, and see if there are differences you can find. I think you will have a much better chance of success.

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Steve Smith
"Music is what feelings sound like"

This is more of a PHD then a science fair topic

But good luck with it.

I think steve has a good point,. I've built ladder and x-brace guitars and they are very different from each other. You may even be able to build a simple model to illustrate the difference. It would be interesting to build a guitar body such that you could have interchangeable tops that clamp on for example some how. Wouldn't even really need frets just tune to an open chord.

IDK just thinking out loud here.

Hi, again, Cameron,
As I read these responses, an idea came to mind: You don't really need a fancy guitar body to explore and demonstrate the different bracing patters. You could do it with two or three wood cigar boxes. Remove the tops, turn them over so that the bottom becomes the new top. Cut identical sound holes in each one. Then brace them with basic variations: X-brace, fan brace, ladder brace, etc. You can rig up a simple neck and bridge for each. What I'm describing here is essentially a cigar box banjo or ukelele. You can find lots of information on cigar box instruments with a web search. I think they would be very appropriate for a science fair project, and, to a degree, I think you could produce audible differences in sound. Materials should be fairly easy to find and inexpensive, and then you can make your project as basic or as complex as you wish.
Looks to me like you already have some interested fans out here, so check back for advice and suggestions as you go forward. When you're finished, I hope your post your results, too. I'm rooting for you!
Patrick

For a science fair presentation, visuals seem to work best rather than words. If you can afford it, I'd suggest Alan Carruth's DVD on free plate tuning. He demonstrates those principles on pieces of styrofoam, raw wood, and guitar tops. He uses a signal generator built specifically for this purpose, but you could do as well with a free piece of signal generator software and an old stereo for amplification. It could make for a dramatic presentation, if you could find a way to deal with relatively high amplitude. If you search on youtube for Chladni patterns, you can get an idea of the visuals. This could tie in with how the bracing affects the sound in demonstrating how the test piece response to different frequencies changes as the bracing is shaved down, for example.

Good luck, and let us know what you come up with.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

+1 for Alan Carruth's DVD

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EddieLee

Most of the research I've seen suggests that bracing patterns per se do not have as big an effect on sound as some other things, such as the size and shape of the body. This assumes that the bracing is done reasonably well: badly done bracing of _any_ pattern can ruin the sound in a hurry.

It's interesting that a spruce top with no bracing will vibrate in much the same way that a properly braced top will. In theory you could just leave the top thick and it would sound fine. The problem is that it would be heavier than a braced top would be, so it would not be as loud. So that's what bracing is about: it's there primarily for structural reasons, rather than sound. I think it's no accident that the two most successful bracing patterns, the Torres 'fan', and Martin's 'X' bracing, concentrate wood right where you get the most distortion under string load: between the bridge and the sound hole.

That said, we also note that fan bracing is much more successful on Classical guitars, and X bracing on steel strings. Nylon strings tend to be relatively deficient in high frequency energy, and Classical guitars need to make the most of the small amount of high end the strings give you. With steel strings you have the opposite problem: there's a lot of energy in the high frequencies, and you have to get enough bass to balance that. The two bracing systems effect the relative balance between highs and lows in interesting ways, and that's one reason each is more successful in the given application.

As has been said, this could be a huge project, and limiting it in some way would be useful. If you could get together the wherewithal to produce Chladni patterns on completed guitar tops, you could look for systematic differences between some steel string and nylon string guitars, and try to relate that to the differences in the bracing. Chladni patterns make a great demo!

In addition to all the good comments already suggested, I would suggest that one course would be to brace up a few tops using different bracing patterns. You could shave the braces until they all weigh the same and then compare their deflections under load. The one that deflects the least wins!

That's the game in a nutshell - making a lightweight structure that can withstand the string tensions for now, and for the next 50 years.

Good luck!

Trev

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http://www.PeakeGuitars.com

Hi Cameron, have no idea whether this helps or not, but try placing a vibrating tuning fork on a braced top. Then put it on the brace itself. Appreciably louder. Does this suggest that the braces serve some function other than just structure? Might they be considered conduits for the vibrational energy generated by the strings?

Maybe that's a more focused, more easily answered question.

Good luck

Steve

Or, as Alan suggests, maybe they're primarily structure. How would you go about answering that?