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Deflection and Resonance Testing
I have a guitar that I'm willing to sacrifice for the sake of science.
I'm thinking of shaving the braces, but I want it to be a learning experience. I want to understand what is happening to the guitar as I change the brace shapes and sizes. So I'd like to rig up a deflection gauge and some way to measure the resonance frequencies of the top, back, and air cavity. Any suggestions on cheap rigs? For a deflection gauge, I assume one with 1" travel and 0.001" resolution would be sufficient. Various sources seem to have them for under $20. For resonance testing, I assume doing a slow frequency sweep via PC sound card / speaker and measuring the amplitude with a PC-based microphone should work, right?
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gits: good and plenty chops: snickers |
#2
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I believe that is how Woody makes his tops. If he see's this I'm sure he will have some ideas.
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#3
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I'm also following this path and have found these links to be helpful:
http://www.siminoff.net/pages/siminoff_books.html I own The Art of Tap Tuning, and the Luthiers Handbook and have found them to be extremely helpful. http://www.strobosoft.com/index.cfm?...ry=122&sub=189 This software will handle all your tap tuning needs and comes in two versions, lite and complete -both are under 100 bucks. To do this the right way you'll need a force gage, the ability to build some fixturing, and a inch pound torque wrench. Also you'll need to build a master soundboard because you will need some sort of refrence to compare your experiments to. |
#4
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There's a lot of smoke & mirrors about tuning tops.
personally I hold Siminoff's book in the same area as homeopathy. scientifically I cna poke HUGE holes in it and I'm open to be proven wrong but there are a LOAD of luthiers who hold similar (if less forthright) views!! when tuning a top..... and carving the braces........ you have a top that is bigger than the sides...... and is free to resonate (ie. not attached to the sides) so you carve and sand til it resonates at a D. then you glue it to the sides and cut an inch off all the way round...... you want to guess what it'll resonate at, because I haven't got a clue!! Sam Irwin (one of Lowdens original team and now running a luthiers class in Belfast) says forget tuning to a NOTE, just go for a nice musicality of a resonance. if it sounds right then it prolly will be. it IS good to experiment and repeated builds and meticulous note taking will mean that eventually you will be able to predict what a top will sound like once it's complete.
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#5
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Today, I sang into three different guitars and measured the resonant frequency of the air cavity. It was interesting in a few respects: 1) They all resonated strongly at certain pitches, and not at all for others. 2) A parlor resonated at B, one 000 at A sharp, and another 000 at D. 3) I like sound of the one that resonates at D the best. 4) It seems that the air cavity resonates at a lower octave than the open strings. I'm not sure if this is by design, but it seems to keep the sound fairly balanced across the strings. Question: when I sing into the guitar and cause it to resonate, is it resonating at its Helmholtz frequency? I.e., is it just the air that's getting excited? I assume that shaving the braces won't have any effect on this resonance frequency.
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gits: good and plenty chops: snickers |
#6
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I think!!
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#7
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removing wood from the braces will lower the resonant frequency of the top.
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