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Hi, well it's science fair time at my school already and I have been trying to think of something to do. I'm very interested in building guitars and knowing the science behind them. My last two projects where what material makes the best soundboard and what type of bracing is the best, both were very successful. I want to stay in this field for this project but I'm not sure where to start if anyone has any ideas that would be appreciated.

The science of the fingerboard and strings. Why the frets vary in spacing, intonation, harmonics and intervals etc., etc.
Tom

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A person who has never made a mistake has never made anything!!!

How wood bends with applied heat and appropriate force?

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Doug

Don't let fear or common sense stop you from trying to build something

These are all very good suggestions. The first two offer some fairly advanced possibilities. However, for a sheer "gee-whiz" demonstration, I'd go with side bending, too. It seems to me that most people don't question the fact that guitar sides have curves or how they got that way. However, when I start talking about it, they invariably say: "Wow. I never really thought about that before." It's just so visual. It would make a good stand-alone display, and a really dramatic live demonstration. And there's plenty of science involved.
Patrick

Chaldni patterns - I bet you could make a great science fair project -

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It's this new idea from recent decades that everyone gets a participation award. - MUX

+1 for Chladni patterns, where a plate (or guitar back or top) is vibrated at various frequencies and patterns of vibration are indicated by ground coffeee or tea, glitter, sawdust, etc. Frequencies at which the patterns occur are influence by stiffness and mass of the plate.

http://www.phys.unsw.edu.au/~jw/guitar/patterns_engl.html

Simple to set up with a laptop, a small speaker, glitter, a plate to vibrate, and a free sine wave generator application, and it's fun.

Pat

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

If you're talking science and guitars.......Look no further than the C37 Lacquer? (sorry to bring that one up again)

I bet the Chlandi patterns would be a big hit visually. Especially if you set up a top where you could change the bracing during the demonstration to show the effect.....maybe a way to screw a second piece on top of the braces or across the braces.

That would be cool. Small nylon screws would work for that. Even without adjustable bracing stiffness, Chladni patterns would make a pretty striking presentation. It could even be interactive, if you let people twist the knob of a signal generator to change the pattern.

C37 - urgh. Is that stuff still around?

Everybody does like to see Chladni patterns. The trick is to make 'science' out of it. Relating the patterns on the 'free' plates to the way the finished guitar works is pretty convoluted. I'm of the opinion that it 'works', in some sense, and I've been doing it for years, but demonstrating some direct cause and effect relationship is really hard.

On the other hand, the Chladni patterns of the assembled guitar are fairly easy to relate to aspects of the sound in many cases. The drawback here is that most guitars show pretty similar patterns, so you might find it hard to argue that the shapes themselves mean anything. Frequency relationships do seem to matter, though, and that's fairly easy to demonstrate. A particularly nice demo is to look at the usual guitar 'wolf', down around G on the low E string, and show how that thuddy note relates to the 'Air' and 'wood' resonances of the box. You can add mass (use poster putty) in various places to alter resonant pitches, and people can hear the results (or lack thereof) right away.

One problem with working with assembled modes: the higher order ones can take a lot of power to drive. It might be hard to get enough hearing protectors for everybody in the room. Still, with luck, you could make some interesting points just looking at the low order modes.

I think the best (and easiest to grasp) is illustrating the Helmholtz resonances for various sized sound chambers.
I mean why is a bass big and a violin small and a guitar somewhere in between.................??
Most folks have no idea why this is.

Another idea, how about action and intonation? Well known that the cheaper the guitar, the higher the action. you can do this simply with a couple of neck mock-ups, one high action and one low. Just a couple of frets on each will be enough to illustrate the difference, which can be seen, felt, and demonstrated with a tuner. Also, this would be very educational, since it is amazing how many people don't understand it.

And of course it is science, as it relates to string tension, stretch, and how that relates to tone.

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Phil

http://www.oleninstruments.com

"Those who tilt at windmills are only considered insane by those who can't see the dragon."

If I was to do the chladni patterns how would I set it up... I know what to do about how if you changed the frequencies the pattern would change but what would I be looking for?

This YT video might give you and idea of what's involved. The sound generator H uses is pretty spendy, but you could get the same results with a laptop (I'm assuming you already have one), an old integrated amp or receiver from a thrift store, a 4" speaker rated at 20 to 40 watts, and an application like Audacity or AudioTest to generate the sine wave. I like Audio Test (Mac only) because you can vary the pitch in 1 Hz increments with the mouse scroll wheel.

http://www.youtube.com/watch?v=TFEUV0QPfy0

Pat

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

Thanks and one more question, should a brace the soundboard or just leave the plate un braced?

You could go either way, or do both, demonstrating the change from bracing.

Pat

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

Hi, I haven't been on this lately because I've been doing some research on chlandi patterns. Do the patterns differ on a braced top vs a un braved top? Because I could do an experiment to see if they did. Does anyone have an idea?

They certainly do! Usually you will see more different patterns on an unbraced plate than a braced one, and the corresponding patterns, such as the 'ring+', will be at lower frequencies on the unbraced plate. Braces add more stiffness than weight, of course, and also can interfere with some patterns that you see on the unbraced plate. The whole practice of 'free plate tuning' has to do with using the Chladni patterns to get the mode shapes and pitches to be what they 'should' (however you decide on that!) by shaving the braces, and usually when they're 'right' the patterns look a lot like what they would on an unbraced plate.

You could demonstrate the effect of mass on the patterns by simply adding and subtracting mass using magnets stuck together with the top sandwiched in between them.

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Jim Watts
http://jameswattsguitars.com