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Parabolic OM Bracing (pics) http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=10691 |
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Author: | bob_connor [ Thu Feb 01, 2007 6:28 pm ] |
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Hi Folks Just put the braces on a parabolic OM and thought I'd run it past some of the parabola experts as this is the first one I've done. This guitar is a twin. The other one has scalloped braces and they're both EIR with Englemann tops, 24.9 scale and we've tried to keep the specs as close as possible so we can get a good comparison. I intend to record both and throw them up here when they're finished. So here it is. I took the photos with my phone so please excuse the quality. ![]() ![]() Thanks for looking. Cheers Bob |
Author: | Joel [ Thu Feb 01, 2007 7:09 pm ] |
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Are the finger braces and tone bars inlet into the x-brace? This looks like the sort of thing that I want to do on my first (one day I'll get there!). |
Author: | Dave White [ Thu Feb 01, 2007 7:14 pm ] |
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Bob, That's looking pretty good to me. Shape-wise they look nice and smooth. The only way I can judge on my own tops is by tapping around everywhere and listening for a clear sustaining ring everywhere. I'm getting bolder as I build and am bracing lighter and lighter. |
Author: | Howard Klepper [ Thu Feb 01, 2007 7:35 pm ] |
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Well, ending the lower face diagonals so far from the edge is pretty radical. When people say "parabolic" what I want to know is the equation for the parabola or parabolae you used. If you don't know it, then how do you know they are parabolic? |
Author: | Dave White [ Thu Feb 01, 2007 7:43 pm ] |
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Howard, Actually I call mine "triabolic" now which is one step up from "diabolic" ![]() |
Author: | Colin S [ Thu Feb 01, 2007 7:52 pm ] |
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Very similar to my bracing, though I do take the tone bars much closer to the edge, like Howard says. This is one of my recent ones, maybe not pure mathematical parabola, but we all know what we mean. I vary the placing of the peaks on the finger and tone bars slightly differently from yours and I do find it makes a great difference. ![]() Your top should make a fine sounding instrument. Colin |
Author: | JJ Donohue [ Thu Feb 01, 2007 8:19 pm ] |
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Nice and clean! Great experiment and I eagerly await your comparative results. BTW...don't forget to glue on that all important X-Brace Cap!!! |
Author: | bob_connor [ Thu Feb 01, 2007 11:34 pm ] |
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Thanks for the feedback everyone. Joel The tone bars and finger braces aren't inlet into the X - just butted up against it. The top for the scalloped braced OM got glued on this morning and we spent quite a bit of time comparing the tap tone on different parts of the top. When tapped at the end of the tone bars we were getting a G# but in the area where the tone bars meet the X it was a tone higher at B flat. So we trimmed down the braces in that area to try and achieve a similar note all around the lower bout. I haven't spent much time on the parabolic top but I did notice that pitch of the tap tone varies significantly in different parts of the top when compred the the scalloped brace top. I'm going to spend some more time tomorrow playing around with this. The shortened tone bars are a bit of an experiment, Howard, in attempt to free up the lower bout without taking thickness out of the top. The X braces on this aren't going to be notched into the linings in the lower bout either. I've got a little Pro-tools setup with a couple of nice condensers so I will record both guitars when they are finished and post some tunes. Haven't forgotten the cap JJ. I took the photos at 6pm after a 35 degree day and was keen to get to the pub for some fluid replacement therapy. ![]() Again, thanks for the comments guys and will keep you posted with developments. Cheers Bob |
Author: | Serge Poirier [ Thu Feb 01, 2007 11:39 pm ] |
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Bob, you're a NEAT FREAK! ![]() Nice work my friend and i predict a cannon out of this! ![]() ![]() ![]() ![]() ![]() |
Author: | Dave White [ Thu Feb 01, 2007 11:46 pm ] |
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[QUOTE=bob_connor] The top for the scalloped braced OM got glued on this morning and we spent quite a bit of time comparing the tap tone on different parts of the top. When tapped at the end of the tone bars we were getting a G# but in the area where the tone bars meet the X it was a tone higher at B flat. So we trimmed down the braces in that area to try and achieve a similar note all around the lower bout. I haven't spent much time on the parabolic top but I did notice that pitch of the tap tone varies significantly in different parts of the top when compred the the scalloped brace top. I'm going to spend some more time tomorrow playing around with this. [/QUOTE] Bob, I don't bother trying to "tune" my tops to specific notes and expect to hear different ones when I tap around. What I do aim for is that as I go along the braces I want the top in each place to continue to resonate and sustain with no dropping off or dead spots. Sometimes it only takes a little sanding of a brace to achieve this. I also look for a "kick-back" when I tap on the top at the bridge position and leave the tapping finger on the top. I think it is better to use the term "voicing" the top rather than "tuning" which I think can puzzle a lot of people. Interested to see how your bracing experiment turns out. |
Author: | Dave Rickard [ Fri Feb 02, 2007 12:05 am ] |
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[QUOTE=Howard Klepper]When people say "parabolic" what I want to know is the equation for the parabola or parabolae you used. If you don't know it, then how do you know they are parabolic? [/QUOTE] That's right, What are actually they talking about? |
Author: | Kevin Gallagher [ Fri Feb 02, 2007 12:13 am ] |
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That bracing looks very nicely executed. It should yield great results for you. Very neat work, too. Tuning tops to specific notes will prove quickly to be an exercize in futility since every top and every pece of bracing that you use with it will have unique resonant chracteristics. To create the same note on one top can call for the need to remove more or less material than is desired or may have been necessary on another so it needs to be about individual resonance of the top and bracing as a system instead of note achievement. I match bracing and tops to one another according to their fundamental resonant frequencies.....and that's not the note at which each resonates, but simply whether they fall into what would be conidered generally low, medium or high fundamental resonance. It's interesting when we discuss voicing since the number of theories and approaches used will equal or even exceed the number of people presenting them. Damping, mass, shape and placement are all among the many variables that we all are confronted with when we take on the prospect of coaxing a top as close to its tonal potential as we're able to. There is always mass, so there is always damping and we use shape and placement to control and direct the effects of both. Regards, Kevin Gallagher/Omega Guitars |
Author: | Dave White [ Fri Feb 02, 2007 12:21 am ] |
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[QUOTE=Dave Rickard] [QUOTE=Howard Klepper]When people say "parabolic" what I want to know is the equation for the parabola or parabolae you used. If you don't know it, then how do you know they are parabolic? [/QUOTE] That's right, What are actually they talking about?[/QUOTE] As I'm carving my triabolic braces I'm mostly thinking (to quote Wikpedia 'ish): "In polar coordinates, a parabola with the focus at the origin and the top on the negative x-axis, is given by the equation: r(1-cos(theta))= L where L is the semi-latus rectum: the distance from the focus to the parabola itself, measured along a line perpendicular to the axis. Note that this is twice the distance from the focus to the apex of the parabola or the perpendicular distance from the focus to the latus rectum. Whoops ... didn't mean to take off that bit - am I talking out of my latus rectum? ![]() |
Author: | LanceK [ Fri Feb 02, 2007 12:26 am ] |
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MAN! Those are some CLEAN Tops! ![]() |
Author: | JJ Donohue [ Fri Feb 02, 2007 1:10 am ] |
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Dave...you're hilarious! Removing that bit from the latus rectum now changes everything to Hyperbolic Bracing. And when you carve them under extreme pressure they become Hyperbaric Braces. See what you started, Howard! ![]() |
Author: | Dave Rickard [ Fri Feb 02, 2007 2:14 am ] |
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[QUOTE=Dave White] As I'm carving my triabolic braces I'm mostly thinking (to quote Wikpedia 'ish): "In polar coordinates, a parabola with the focus at the origin and the top on the negative x-axis, is given by the equation: r(1-cos(theta))= L where L is the semi-latus rectum: the distance from the focus to the parabola itself, measured along a line perpendicular to the axis. Note that this is twice the distance from the focus to the apex of the parabola or the perpendicular distance from the focus to the latus rectum. Whoops ... didn't mean to take off that bit - am I talking out of my latus rectum? ![]() [/QUOTE] Oh now I understand ![]() |
Author: | Brock Poling [ Fri Feb 02, 2007 3:39 am ] |
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[QUOTE=Howard Klepper] Well, ending the lower face diagonals so far from the edge is pretty radical. When people say "parabolic" what I want to know is the equation for the parabola or parabolae you used. If you don't know it, then how do you know they are parabolic? [/QUOTE] Who knows why things are called what they are called. I agree with your point, but to have a conversation and have everyone understand what you mean it is sometimes easier to use common terminology. ... at least I don't call it "kerfing" anymore. ![]() ![]() |
Author: | Howard Klepper [ Fri Feb 02, 2007 4:25 am ] |
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[edit] Ah, why bother. I'll just go back to cutting my braces to catenaries and arching my tops to piecewise cubic polynomials. My equations are trade secrets. |
Author: | Serge Poirier [ Fri Feb 02, 2007 4:32 am ] |
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Dave is right in his assertion, i'd promulgate further the idea that in order to achieve parabolas, one scientific way would be to use a culbutage riggin' that would be finding it's point of inertia on a junction goupille. |
Author: | Hank Mauel [ Fri Feb 02, 2007 4:58 am ] |
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[QUOTE=Dave White] [QUOTE=Dave Rickard] As I'm carving my triabolic braces I'm mostly thinking (to quote Wikpedia 'ish): "In polar coordinates, a parabola with the focus at the origin and the top on the negative x-axis, is given by the equation: r(1-cos(theta))= L where L is the semi-latus rectum: the distance from the focus to the parabola itself, measured along a line perpendicular to the axis. Note that this is twice the distance from the focus to the apex of the parabola or the perpendicular distance from the focus to the latus rectum. Whoops ... didn't mean to take off that bit - am I talking out of my latus rectum? ![]() [/QUOTE] '' Are you using the standard cubic furlongs per fortnight measurement schedule or the more esoteric mega nanobits per millenium concept for your calculations? ![]() |
Author: | Serge Poirier [ Fri Feb 02, 2007 5:03 am ] |
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![]() ![]() ![]() |
Author: | LanceK [ Fri Feb 02, 2007 5:08 am ] |
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What are you guys talking about ![]() ![]() |
Author: | Serge Poirier [ Fri Feb 02, 2007 5:15 am ] |
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![]() ![]() ![]() |
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