PDA

View Full Version : Tone bars



cornfedgroove
12-02-2009, 05:09 AM
Ok, I've done the search and came up empty, and as long as I've been here I dont recall this topic. I'm sure its been done.

I find myself contemplating tone bars...I cant say that I understand their purpose. I've done a little google searching but its always forums talking about the "hows" rather than the "whys". I'm just looking for some tone bar theory. Here's what got me thinking:

I made that mandolin and it seemed to have resonated almost "too much". You figure 8 strings crushing a bridge into a small cigar box lid...makes sense. Granted, it was better than a $100 mandolin (brings me little satisfaction since they are crap)...it was not better than a $500. I need to rein in and focus the resonation a bit, to clean it up...I had considered dampening it somehow, then it hit me that THAT might be what tone bars kinda do. Help me out and throw me some basic 'what and why' for tone bars. Am I off base?

ukantor
12-02-2009, 05:48 AM
You are thinking along the right lines CFG. I built a soprano uke with no lining or bracing, just to see what would happen. It was much as you describe. Lots of sound going on. If strummed gently it sounded fine, but giving it a bit of welly produced a rather strident, muddy sound.

Those vibes have got to be damped, but not too much. It's a balancing act.

John Colter.

buddhuu
12-02-2009, 05:52 AM
If you want to know about tone bars, I suggest popping over to Mandolincafe.com and asking in their builder/repair forum. There are some heavyweight luthiers and acoustic science academics over there. Very helpful people.

buddhuu
12-02-2009, 05:55 AM
Yoink... Just nipped over myself, and I see you've already been there, CFG! :D

cornfedgroove
12-02-2009, 06:12 AM
Yoink... Just nipped over myself, and I see you've already been there, CFG! :D

LOL..np brutha'. I JUST joined there last night...you'll notice my posts are all spanking new

Bradford
12-02-2009, 10:18 AM
Hi CFG, let me see if I can help. The first thing you need to understand, is that braces, like any other design feature, need to be incorporated into the overall design. The thickness of the top, the arching of the top, the graduation of the top and the shape of the top all contribute to the quality of the sound produced as well as any bracing. Great instruments are great because the builder has balanced all of the variables into a whole design. That said, will braces help, quite possibly. Generally speaking, with braces, they are added for structural reasons, to keep the top from deforming under the string load. The early Gibson oval hole A model mandolins are marvelous sounding instruments, but over the years many of their tops have collapsed because of insufficient bracing. Besides structural reasons, the other function of braces is to help the entire top vibrate uniformly, like the diaphram of an air pump. The idea is to get the entire top to move up and down with the string vibration. I would suggest an H bracing pattern, with a transverse bar under the bridge and two side braces going the length of the top on either side of the sound hole. I would start small at first, a cross section of 3/16" x 3/8" tapering toward the edge of the top is a place to start. Hope this helps.
Brad