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| Parabolic and scalloped braces http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=1018 |
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| Author: | Colin S [ Fri Feb 11, 2005 1:03 am ] |
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Wade asked about the bracing on my new OM, and why I had gone with parabolic struts for front and back. I have listed below my thoughts on bracing in general for you experts to tear to pieces. Bracing is probably the most discussed topic over here amongst luthiers, and is felt to be the area that most experimentation should be taking place. I must admit that I don’t follow all the physics of it but the engineering faculty at the university where I work intuitively feel that a scalloped system should produce a more complex harmonic range, whereas a parabolic system should produce purer fundamentals and more projection. Think about it, do you use a scalloped X brace because Martin put one in or have you a reasoned argument for using it? Soundboard My soundboards are generally braced in the normally pattern. An X-brace system is used with two tone-bars behind the bridge and two finger-braces either side. I use two main brace profiles. I believe the traditional Martin style scalloped braces produce warmth, responsiveness and sustain while still giving reasonable dynamic control, whilst parabolic systems allow a quicker response from the top and produce a faster, more explosive attack with more brightness. If I use scalloped struts I use relatively high narrow pointy struts which I feel help a great deal with producing the higher overtones whilst still allowing an open and free sound. Try tapping all over the top of your strung guitar, I bet you will hear a dull sound where the points of the scallops are. Top thicknessing is generally uniform but sometimes I taper gradually from the central joint if I am trying to modify the relative lengthways to crossways stiffness of a particular top. Top bracing: 'Scalloped' standard scalloped struts. I feel this produces a good balance of depth, warmth, and enough brightness to produce a versatile instrument that will strum and flat-pick and still respond reasonably to fingerstyle. With Sitka Spruce it biases to plectrum work and stronger fingerstyle players, with European or Englemann it becomes more responsive to gentle fingerstyle and with Cedar a big warm sound is produced. 'Parabolic': parabolic X and tones, and parabolic fan struts instead of fingerbraces. This system produces a very explosive sound but with less sustain in the lower mids, making a guitar that responds quickly and clearly for complex modern fingerstyle playing with plenty of string control for slack tunings such as DADGad. The tone is very rich, and modern techniques such as tapped harmonics love it. Usually built in Cedar or European for most people or Sitka for harder players. Good in larger instruments like Jumbos. Don’t forget the braces should be parabolic in cross section as well 'Hybrid': a parabolic X brace and scalloped tone bars. Produces a controlled feel like the full parabolic system but with a slightly richer tone. Works very well for guitars where extra string control is needed for slack tunings, or if you use very light string gauges (10's or 11's which I always do) I feel that it helps to control the lower mids for Cedar topped guitars whilst still producing a big open sound. My personal favourite system of the moment. 'Semi-Scalloped': Very similar to the standard scalloped system but with a parabolic treble side X strut. Its felt that this can help add some extra definition for harder players or contain the basses of larger guitars. ‘Golden era’: Medium to thick top with scalloped strutting and quite low tone-bars behind the bridge. These produces the classic US sound, suiting Bluegrass, Travis picking and other ‘American folk’ styles. If you are interested in the theory of parabolic bracing look at Scott van Linge piece on parabolic systems. Read with the usual questioning sceptical mind. I don't believe it to be a panacea for all evils as he seems to! But it does explain the concept. Back: Four or three transverse bars made from mahogany to help with richness and warmth or spruce for a brightness. For most guitars the bars are triangular or parabolic in cross section and with moderate scallops at each end to give a good combination of depth, warmth and richness to tone without boominess. For my Celtic type sound I use 'parabolic' back struts with no end scallops to give an extra explosive kick to the sound. Recently I have started to replace the lower bout struts with a light parabolic X brace, so that the lower bout back acts more like a speaker cone. Thicknessing of the back is usually uniform but sometimes a taper from the centre joint outwards at the lower bout, particularly with parabolic braces. OK, that’s my two-penny worth, now gloves off and come out fighting! I’ll step back out of the way and let you all slug it out. Colin Scott Van Linge parabolic bracing |
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| Author: | Dickey [ Fri Feb 11, 2005 1:28 am ] |
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Colin, your thesis contains the wisdom of the ages, so I'm inclined to give it a hearty, "Way to Go!" Van Linge's article of guitar brace knowledge is interesting too. All I know is that the scalloped braces "ala Martin, pre-war" are doing some incredible work both structurally and tonally. Also the species of Picea Rubens appears to be what the doctor ordered in the top bracing scheme. Thanks for sharing your knowledge and observations. |
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| Author: | LanceK [ Fri Feb 11, 2005 1:34 am ] |
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Colin -- Thanks for that information. I'm going to read and reread it to try to digest it all, then apply some of it to my building. Ive been building with the standard martin x Brace, scalloped. Id like to try the parabolic bracing and see how it effects my guitars. Thanks again. |
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| Author: | Colby Horton [ Fri Feb 11, 2005 1:58 am ] |
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Same here, I've got to read over that info some more and see what I can get out of it. Thanks Colin. |
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| Author: | ejones [ Fri Feb 11, 2005 3:21 am ] |
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Help me visualize parabolic braces. I think I understand the cross-section...sort of like a cathedral window? But what about along the length of the brace? I can see the scalloped shape along the length, but what would the parabolic shape look like? Full height at the X intersection and tapering off on a parabolic curve to nothing at the extremitites? 
Okay, I see the brace shapes in Van Linge's article. Duh. 
Eric |
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| Author: | stan thomison [ Fri Feb 11, 2005 3:48 am ] |
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Colin thanks for the information. Articles like this is what as one of my grandsons would say makes this forum "rock". What an asset you are as all the others here who contribute a wealth of information |
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| Author: | Colin S [ Sat Feb 12, 2005 11:41 pm ] |
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I think I've frightened you all! What I really wanted to say, and this mainly applies to the hobby builder, is always think about every part of the guitar design, don't just go with the 'Martin' bracing because that's what everyone else does, think about what type of sound you want the guitar to produce and then select the materials and internal design to produce that sound. The sound comes first everything else is subordinate to that. Yes, if I was building a D-28 to flat pick ( no I won't!) then yes I would use Martin style scalloped struts. But for most finger style work in smaller bodies I believe there is a better alternative that should at least be considered. Right, off soap box, back to cooking the Lunch. Colin |
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| Author: | Wade Sylvester [ Sun Feb 13, 2005 1:16 am ] |
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Colin, Thank you so much for the details! These are the things I have been thinking about going into the next few builds. Some of my hesitation to dive into the next project is knowing the choices but not knowing which is best or appropriate. This really helps! Wade |
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| Author: | John Kinnaird [ Sun Feb 13, 2005 4:38 am ] |
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The more I think about top bracing the more I get away from scalloped bracing and lean toward parabolic bracing. I believe tops need to be light and stiff. Especially stiff near the center and pretty flexable near the perimeter of the top. The supports for the top are, of course at the edges, and the load on the top is in the center. No engineer in their right mind would use scalloped braces to support that load with minimal material. (minimal material means lighter tops) The only time I scallop is if I see that I over braced the top and need to make it a little more flexable. Now I'll duck and run John |
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