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Raising resonant frequencies of a new build
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Raising resonant frequencies of a new build
Initial frequency analysis of this D28 copy (done with a temporary 35g bolt-on bridge and the back plate taped on) is VERY LOW. Main air resonance 83.5hz and top monopole 156.6. It’s standard Martin scalloped X-bracing with a torrefied Adirondack top. Since I can still easily access the bracing, I’m thinking of going in and laminating wood on top of the X brace to stiffen it. Other options would be a very light bridge, though I’m not sure how much I can reduce it or how much effect that would have. I’m not real eager to enlarge the sound hole. I was planning to thin out the perimeter of the top, but that doesn’t now seem wise.
As-is, it seems like I’ll be creating a real bass boomer. Monopole mobility currently calculates to 21.7.
Any other options/advice will be greatly appreciated.
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2 Replies
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I think raising it is very difficult to impossible, not sure but I think that’s what Guiliano said.
My recent guitars have been crazy thin and have insane monopole mobility and sound great. They aren’t structurally as stable as I’d like so I need to dial back but they sound amazing.
Personally I’m a believer in finishing the guitar in front of you and learning your lessons. But this is a big reason why I’m planning to switch to glueing my tops on first and then shaping my braces and potentially sanding off some top thickness after the top is glued to to the sides, I will have a lot better idea how things are going to move (I’m using structured sides so don’t really need to be in the mold). I think (Hope?) that this will be a really cool thing.
The guitar might sound amazing.
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Update: Turns out it’s not impossible to raise the frequencies. Removing the 35g temporary bridge raised the air resonance 2.1 hz and top monopole 2.6 hz, so a lighter bridge could help a bit.
Filling in the scallops on the lower portion of the X-braces by splicing in spruce raised the main resonances 3.7, 8.6 hz respectively, but after crowning the tops of the splices it dropped down to about half that, making me wish I had glued in even taller splices. So, I’m still at 85.3 hz and 162.4 hz.
In addition, the top monopole appears to be very weak and filling in the scallops appears to have boosted the cross dipole significantly (based on tapping on the antinodes, I don’t have Chladni equipment). Here’s the analysis (red = scalloped, blue = rough splices, green = trimmed splices.
I went ahead and glued up the box with the trimmed splices. I’ll use the lightest bridge possible and hope for the best. It’s all rather mind boggling!
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