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I have a patteren (template) I use for my f holes. I've experimented a little with different sizes but not while the mandolin was strung and tuned to pitch. Do you start with the ends of the f hole or the complete outline? How do you know when to quit? .So if someone could describe the sound hole tuning theary and how to know when to stop I would appriciate greatly. Thanks everybody, Bryce
Dale Ludewig
May-08-2005, 3:27pm
If it were me, I'd leave the end holes alone. You can fiddle (pun intended) with the sides of the f-holes. However, you're dealing with body cavity resonance here (Helmholtz?)- I think you have a fairly large, within reason, leeway before the sound of the instrument is affected to any great degree. At the extremes of small vs. large, you'll notice a difference. After doing my best before stringing up, then if you "have" to, you can adjust the sizes. But remember, once the hole is larger than it was, you can't make it smaller! In general, of course, the larger the f-holes, the higher the resonant frequency of the body cavity. I think if you just stay within the accepted size of the f-holes, you have nothing to worry about. Make your mandolin!
oldwave maker
May-09-2005, 6:57am
An early resonant frequency alteration experiment: before chainsawing off this top I was able to raise the Q a half step! both f holes were this size. I sure get a kick out of ebay mando ads stating that the sound chamber was tuned by altering the size of the f hole. Makes more sense to make the body 1.73" thick.
Dave Cohen
May-09-2005, 9:49am
Bill, a tip of the hat to you for making graphic what I have been trying to get through for at least a coupla years now! #BTW, that kind of snake oil is also seen in places presumed to be more reliable than ebay. #I have made the mistake of citing the formula for Helmholts resonance frequency and giving samples of numbers calculated from the formula. #Your picture is way more effective. #We live in a math-averse society (sigh).
Question: What do you mean by Q? #If you are referring to the Helmholtz resonance frequency, that usually goes by f0 or occasionally A0. #Q is the term for (sorta) internal losses in a structure, and while it is dependent on frequency, it is probably not what you are changing by enlarging the soundholes. #BTW, changing the body volume is also a slow way to change the Helmholtz resonance frequency. #If you changed a mandolin body depth from 1.5" to 1.73", the Helmholtz resonance frequency would only drop by about 7%. #So if it were, say, 285 Hz at the 1.5" body depth, it would only drop to about 267 Hz if you increased the body depth to 1.73". #In musical terms, that corresponds to dropping from about a D4 to about a C4, i.e., only one whole step.
I guess I don't have to feel to bad about never tring this. Come to think of it I believe it was in the Siminoff book that I read it. Anyhow, Thanks for advice/input. Second opions are always helpful. And in this case time savers. Thanks, Bryce