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| X-brace scallop peak and valley locations http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=23530 |
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| Author: | David Malicky [ Fri Aug 21, 2009 2:41 pm ] |
| Post subject: | X-brace scallop peak and valley locations |
I've noticed a fair bit of variability for where makers put the valleys and peaks on scalloped X-braces. For example, the Martin's I've looked at have the lowest part of the valley behind the bridge; Taylors dreads put it even with or slightly in front of the bridge. Most seem to put it around the bridge or slightly behind? (Structurally, a valley behind the bridge is of course better, but Taylors would indicate it's still strong and stiff enough in front.) Does anyone know how these choices affect tone, or are there any good guidelines for peak and valley location? Thanks, David |
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| Author: | JasonM [ Sat Aug 22, 2009 3:39 pm ] |
| Post subject: | Re: X-brace scallop peak and valley locations |
The best explanation I heard is that the first guy that did it to his Martin was limited by how far he could get his arm in the soundhole to thin out the braces with his jackknife. The lightening of the braces opened up the instrument, so others followed with scallops without really thinking about why. Many more followed blindly, leaving peaks of wood out near the rim where they have no structural or tonal purpose. The more I thought about that explanation, the more I think it's true, or some variation thereof. Switched to a tapered leg, noticed a gain in responsiveness, and haven't looked back. Can't say for sure if it's the switch in bracing that did it, but I have yet to hear a compelling reason for putting peaks in places where the structural demands are being transferred to the rim. A gradual taper to the rim makes a bunch more sense to me. |
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| Author: | Darryl Young [ Sun Aug 23, 2009 12:30 am ] |
| Post subject: | Re: X-brace scallop peak and valley locations |
David, This is only my opinion.....so take it for what it's worth. A free plate vibrates different than a plate with the perimeter fastened. Of course the rim holds the top in place around teh perimeter which forces it to vibrate with specific patterns. Many of these patterns have a nodal point somewhere between 2" - 3" from the perimeter (roughly). By nodal point, I mean that part of the soundboard isn't moving while the top vibrates. The peaks on the outer portion of the braces seem to correspond to the location of these nodal points. In general, the braces in the middle of the guitar need to be thicker to create enough stiffness to resist the pull of the strings. The scalloping tend to be between these two locations.......between the node lines around the perimeter and the taller, middle portion of the braces that needs strength. Exactly how far from the intersection of the X-brace the scallop can start.....and how fast the braces can be tapered?.......your guess is as good as mine. I'm sure experience and making the mistake of going too far provide valuable insight. |
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| Author: | David Newton [ Sun Aug 23, 2009 8:54 am ] |
| Post subject: | Re: X-brace scallop peak and valley locations |
You haven't said what kind of guitar you want to scallop the braces on, and for the purpose of this thread, maybe it doesn't matter. The variability you have seen in different guitars with scalloped braces is because each maker has a different idea of what they are trying to accomplish by cutting away the main braces. Is a long tapered brace better or worse than a brace with peaks and valleys? No, but each will give a different response to the string's energy. You should study a lot of scallop pictures, and try to imagine what the effect is of the different patterns you see. When I am going to scallop a tops braces, I stare at the braced plate for a long time and by knowing what the top wood is like, and what the sound I am aiming for on this guitar, I wade in and cut. What if I had made the lower peaks 1/8 or 1/4" further up, or back? How can you know, but by having shaped many guitars that you have made, and gotten a sense of what works for you. On your first, you should copy what seems to be a successful pattern done by someone who has done it many times, and I don't mean to copy me. |
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| Author: | David Newton [ Sun Aug 23, 2009 1:45 pm ] |
| Post subject: | Re: X-brace scallop peak and valley locations |
Here's an example of a 000-sized guitar with a nice stiff sitka top. I can't remember the thickness of the top at finish, but close to .115". It is a very sweet, open, woody sounding guitar with quick response (short scale) nice deep bass, maybe a little thin in the trebles. It can, however, be over-driven if flat picked very hard. What does that description and the picture tell you? Perhaps it was scalloped too deep? What about the peaks, valleys and beginning and end of the scallops? |
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| Author: | David Malicky [ Tue Aug 25, 2009 1:22 am ] |
| Post subject: | Re: X-brace scallop peak and valley locations |
Thanks for the replies, feedback, and pics, all. I'm building dreads. Yeah, JasonM, that sounds like a very compelling explanation for how someone stumbled onto the scallop and peak design. It's certainly not a constant strength or constant stiffness design from an engineering standpoint. My understanding is the same as Darryl's, that the peaks help further define a natural node point/line 3" in from the periphery. Looking some more, the peak locations seem more consistent among makers, but not so the valley locations. Yes, it sounds like this one is in the "build it and find out" and "what works best for one maker may not work for another" categories. |
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| Author: | David Newton [ Tue Aug 25, 2009 9:30 am ] |
| Post subject: | Re: X-brace scallop peak and valley locations |
I have never heard that scalloping evolved from someone working thru the soundhole. Interesting, but doubtful. David, your reply indicates you aren't seeing the top and all it's components as a whole, you are only looking at the main X. I would posit that the scalloped brace does give a more constant strength and stiffness to the top along it's entire length, when combined with the other elements. In my example top above, on the treble side, look how the main brace tapers down where the small braces & bridge plate intersects it, and rises to it's peak where it crosses an area of no other braces, then tapers down again where the tone bars come in to it. If you believe the treble notes rise from the treble side of the top, the main X leg is "evening out" the stiffness of the top on the treble side, but to an average higher stiffness than the bass side, considering all of the elements. My mentioning where the treble notes (or bass notes) originate is not important, only that the reasoning behind shaping braces at all is an exercise in controlling and varying them for tonal purposes, considering that they are primarily structural. |
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| Author: | Burton LeGeyt [ Tue Aug 25, 2009 9:39 am ] |
| Post subject: | Re: X-brace scallop peak and valley locations |
I have noticed when running Chladni testing on the thicknessed but unbraced top that many lines intersect right at the point where the peak of the x brace usually occurs. This is also a point where the tone bars and finger braces run off of the x brace. I have been trying to mark this point and work my peaks around them. I figure of the wood wants a node there, I will give it to it! Actually, I don't think it works like that but I found it very interesting. I usually put my lowest point right under the bridge wings but I don't deeply scallop, the peak comes back up a bit but not by much. David, I still have not had a chance to work with the wavesurfer much. I did a little and your advice helped ALOT. When I have a better handle on it I will report back. Thanks again! |
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| Author: | John Platko [ Tue Aug 25, 2009 10:30 am ] |
| Post subject: | Re: X-brace scallop peak and valley locations |
JasonM wrote: The best explanation I heard is that the first guy that did it to his Martin was limited by how far he could get his arm in the soundhole to thin out the braces with his jackknife. The lightening of the braces opened up the instrument, so others followed with scallops without really thinking about why. Many more followed blindly, leaving peaks of wood out near the rim where they have no structural or tonal purpose. The more I thought about that explanation, the more I think it's true, or some variation thereof. Switched to a tapered leg, noticed a gain in responsiveness, and haven't looked back. Can't say for sure if it's the switch in bracing that did it, but I have yet to hear a compelling reason for putting peaks in places where the structural demands are being transferred to the rim. A gradual taper to the rim makes a bunch more sense to me. I think this is very wrong, misleading, and demonstrates a complete lack of understanding of what happend. It's common knowledge that he reached into the soundhole with a finger plane and THAT's how scalloping started. But on second thought, you were pretty close. |
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