WoodyMcKenzie
Mar-14-2004, 4:50pm
I am trying to understand how tone bars work and have a few questions, mainly about symmetry. First, just a few statements to find out if my thinking is straight:
1.) Braces act more as stiffeners than braces. The top should hold up to string tension even without the tone bars.
2.) Several different approaches are successful.
3.) These "plate stiffeners" ought to be made of stiff material that is also light. (For example, a cedar or redwood top that isn't terribly stiff should have spruce tone bars or even something with carbon fiber.)
I understand that most makers are copyists with regard to the parallel type tone bars of Gibson Loar instruments, but if you look at these as plate stiffeners, then shouldn't the tone bar on the treble side then be larger and stiffer than the bass side? Shouldn't the bass side be left to vibrate more "freely"? This may show my ignorance of how tops vibrate, but is there really a difference between one side of the top and the other when considering how the whole plate vibrates? Vibrations travel through all of the bridge and I don't think there is a great division just because the treble strings are on one side of the bridge and the bass strings the other. If all this is so, then is it perhaps safe to conclude that those parallel tone bars are of different dimensions because it helps to have a top that is *assymterically* stiffened?
I am just a novice on acoustics, but I can't help but wonder about these kinds of things. Right now, I am getting ready to put tone bars in a top that I have carved and I will probably X brace it. This system seems like a really good stiffening system and I have had good luck with it so far. I also had good luck copying David Cohen's very different system on one mandolin. But this symmetry issue makes me wonder whether I should make the X bracing assymetrical. Do other builders do this? Do any of you try to adjust the tone of your mandolins by somehow modifying the tone bars in situ? Who out there really experiments with bracing?
Thanks for any advice you might add!
Woody
1.) Braces act more as stiffeners than braces. The top should hold up to string tension even without the tone bars.
2.) Several different approaches are successful.
3.) These "plate stiffeners" ought to be made of stiff material that is also light. (For example, a cedar or redwood top that isn't terribly stiff should have spruce tone bars or even something with carbon fiber.)
I understand that most makers are copyists with regard to the parallel type tone bars of Gibson Loar instruments, but if you look at these as plate stiffeners, then shouldn't the tone bar on the treble side then be larger and stiffer than the bass side? Shouldn't the bass side be left to vibrate more "freely"? This may show my ignorance of how tops vibrate, but is there really a difference between one side of the top and the other when considering how the whole plate vibrates? Vibrations travel through all of the bridge and I don't think there is a great division just because the treble strings are on one side of the bridge and the bass strings the other. If all this is so, then is it perhaps safe to conclude that those parallel tone bars are of different dimensions because it helps to have a top that is *assymterically* stiffened?
I am just a novice on acoustics, but I can't help but wonder about these kinds of things. Right now, I am getting ready to put tone bars in a top that I have carved and I will probably X brace it. This system seems like a really good stiffening system and I have had good luck with it so far. I also had good luck copying David Cohen's very different system on one mandolin. But this symmetry issue makes me wonder whether I should make the X bracing assymetrical. Do other builders do this? Do any of you try to adjust the tone of your mandolins by somehow modifying the tone bars in situ? Who out there really experiments with bracing?
Thanks for any advice you might add!
Woody