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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

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Bob Connor
Geelong, Australia

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!).

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If God had wanted us to drink beer, he would have given us stomaches.

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.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

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?

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Howard,

Actually I call mine "triabolic" now which is one step up from "diabolic"

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

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

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

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!!!

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JJ
Napa, CA
http://www.DonohueGuitars.com

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

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Bob Connor
Geelong, Australia

Bob, you're a NEAT FREAK!

Nice work my friend and i predict a cannon out of this!

[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.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

[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?

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Say what you do, Do what you say.

    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

[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? "

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

MAN! Those are some CLEAN Tops!

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Lance@LuthiersForum.com

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!

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JJ
Napa, CA
http://www.DonohueGuitars.com

[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

_________________
Say what you do, Do what you say.

[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.   

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

[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.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

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.

[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?

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Hank Mauel

What are you guys talking about

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Support the OLF! Bookmark our STEWMAC link Today!
Lance@LuthiersForum.com