Thanks so much for your efforts in putting these together Robbie. I'm a video editor, so well aware that even a simple show takes a lot of time to create, and yours are well thought out, and well presented. I know there are a bunch of us out there who appreciate them greatly.

Looking forward to your thoughts on voicing!

Very interesting video.

I'm looking forward to the voicing video but wondered if you'd elaborate a little bit on the comment about placing the peaks of the scallop at the node line, I assume for the closed ring mode which would probably be about there. I would think that the addition of mass there would favor that mode over other modes where there might not be a node at that point. At least I would think it would lower the amplitude of modes that didn't have a node along that contour.

So are you trying to favor that mode or are you shooting for something else entirely?

you can certainly analyze this stuff to death.

Yea, that darned engineering degree can drive one in that direction .

I'm trying to learn the "Whys" of stuff primarily because I don't build guitars (although I'm building one now) and there are no good plans or direction for the instrument I do build so I figure if I can understand a little about how a guitar works perhaps I can transfer that knowledge to bandura, or at least make better guesses. My current bandura design works pretty well but can certainly use some improvement/refinement.

I just went down stairs, held the top in the upper bout sweet spot and tapped the top for the guitar I'm building right now and could get a large variety of tones depending on where I tapped. I also held the X-brace about where you peak them and I could definitely spot the node you were speaking of right about where you said. The tap tone there was definitely louder and less damped when I held it in the right spot but was lacking the bottom end that it had when holding at the sound hole or the sweet spot in the upper bout.

To further explain my question a bit, the way I see it is this - from a structural standpoint (i.e. resisting bridge torque) I don't think that the peaks of the scallops are helping you very much. i.e. you could probably cut the peaks down to be the same height as the thinnest part of the brace and you'll still get mostly the same "strength" in the top (That's probably not entirely true but for the most part would be correct - weakest link sort of thing). I think we all agree thought that less isn't always more in the case of tone and adding mass can sometimes help rather than hinder.

If we look at these pics: http://www.phys.unsw.edu.au/~jw/guitar/ ... _engl.html one can easily see that sweet spot up in the upper left/right you were speaking of - a lot of modes have that spot as a node. Holding there and tapping must let a lot of the modes ring leading to a full sounding tap.

On the other hand, the area 3" in from the rim along the X-brace and tone bars don't seem to show up in very many of the modes - At least not to my eye. It does however show up in the mode at 221Hz (I think it's called ring and a half). I also recall reading that guys Like Al Carruth try to "close" that ring when it's open like the one in the link. That's implying to me that this is an "important" mode for the tone he's after.

I'm thinking leaving the mass in the peak at that node line should have less effect on that mode and any other mode which has nodes there but would lower the amplitude of modes that have antinodes in that spot. I can't really guess what the added stiffness in that local area would do but you'd think it would have to do something for tone as well (hopefully Al will chime in as I seem to recall reading a post of his a while back that directed how to shave to get certain effects in the chladni pattern). The more I think about it, it could be that the stiffness is way more important than the mass since shaving only changes mass linearly while it changes stiffness exponentially.

Here's a swag hypothesis I just came up with:

Thinning the braces loosens the top for added bass, but perhaps doing it by scalloping rather than just uniform thinning suppresses some, but not all of the lower frequency modes while favoring the "ring and a half" (if that's what it's called) to give the instrument a more balanced tone. Or to put it another way, a tone we like.

Thoughts?

p.s. sorry to ramble but it's difficult for me to get a grip on this stuff.

What I am trying to convey in the video is to not try and re-invent the wheel.

Robbie,
Should all braces that come in contact with the x-brace be glued to the x-brace, or just the tone bars and the finger braces? In the video I thought I saw you applying glue to the end of the soundhole braces? Thanks again.

Ron M.

Great video Robbie as always.I`d love to be able to save that on my computer somehow.
James