Top bracing, let's see em

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Rod True
Siberian Tiger
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Top bracing, let's see em

Post by Rod True » Wed Oct 10, 2007 1:56 pm

So Hesh doesn't blame me for changing topics in his "show us your joints" thread I figured I should start a new topic on top bracing.

So, I'm just going to post my top here and lets have at it.

I've got a rather lightly braced guitar being built right now with all 1/4" braces (but for the two UTB's) on an OM with a cedar top.

Here it is, I don't think I'll be in trouble but we'll see in time.

Don't know if any of you remember, Bruce Dickey started a topic on the OLF based on this top. Here it is, it's got lots of great discussion about bracing. We should talk about it here to if you all want.

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Bob Connor
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Post by Bob Connor » Wed Oct 10, 2007 9:25 pm

Here's a pic of the top from that Myrtle OM we just finished.

Apologies for the out of focus pic but it's the only one I've got of this guitar.

The top of this is quite thin, 2.2mm, but it was a very stiff Engelmann top.

We left the braces a bit heftier than we normally do and because the top was so thin there is a small hardwood brace just behind the bridge plate to help with any bellying that might occur.

In fact we've chucked this brace on the two 12 strings we're building at the moment for the same reasons. I haven't seen that that extra mass in the centre of the soundboard has affected the tone detrimentally.

If you have a look at the intersection of the X and tone braces there is still about 2.5mm thickness on the tone brace. On a thicker top we would feather these down to nothing if we felt the top needed it.

And we simply tap the top until we get an even sustaining note consistently around the lower bout. I actually pay a lot of attention to the note that I get from tapping in the bridge plate area on the premise that this is where the strings are attached.

Both Dave and I cast an ear over the top before we commit to gluing it.

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This is the brace that sits behind the bridge plate.

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Bob

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Dennis Leahy
Blackwood
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And now, for something completely different

Post by Dennis Leahy » Wed Oct 10, 2007 11:54 pm

I'm not sure this is what you were hoping to see, as this won't help much in a discussion about X-braced tops. This was the experimental "pivoting radial" design I used for my guitar.

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The idea was to have a single lateral brace that allowed the bridge to pivot longitudinally (neck to tail), and the radial braces were to quickly move the vibrations across the entire top.

My understanding of what bracing really does sonically is somewhere between crude and non-existent. I try to envision waves of vibration traveling through the braces. When I see the peaks of scalloped braces, it makes me think that it will form a node (area of vibrational inactivity.) I did a crude Chladni test on this guitar, and it made me want to remove the humps at the bridge end of my radial braces, to allow move movement near the bridge. So, that one "refinement" is what I'll try next.

Note that this guitar also had structural braces floating beneath the top, plus a tailpiece. So, the braces did not have to be as strong as a normal, X-braced guitar.

Again, this is all experimental, and I'm not sure it is valid in this discussion.

Dennis
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Alain
Myrtle
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Post by Alain » Thu Oct 11, 2007 12:15 am

Dennis, that is very cool! Is she strung up yet? If so, how's her tone and volume? My hats off to you sir to be bold enough to try new ways to skin that old cat...

Kay, here's the braced top for no.3, a smaller bodied Grand Auditorium'ish type guitar.

Notice that the upper brace is at an angle. I had to make it that way because of the Florentine cutaway...ahh...I ment to do that...really! :wink:

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I did take off a bit more from the lower braces. Although relatively high, they are very thin. Even the X is no more than .25 thick. Everything glued with HHG, of course!
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Dennis Leahy
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Post by Dennis Leahy » Thu Oct 11, 2007 12:36 am

Alain wrote:Dennis, that is very cool! Is she strung up yet? If so, how's her tone and volume? My hats off to you sir to be bold enough to try new ways to skin that old cat...
Thanks, Alain. She is strung up now, for over a year.

Of course, this being my first guitar, and my one and only guitar so far, and the fact that I engineered it, makes me way too prejudiced to accurately describe the tone. Being as objective as I can, I'd say it may lack some of what many describe as "sparkling highs", though no one else tells me that. I'd say it is exceptional in bass and mid bass through mids. The volume is high, and the sustain is exceptional. The experiment was enough of a success to prompt me to want to build more guitars using these concepts.

Dennis
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Sam Price
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Post by Sam Price » Thu Oct 11, 2007 3:12 am

Well today I am wearing a wine coloured cotton indian top with embriodery and a dark green fleece jacket...

Oh sorry... :oops: :wink:

Well, here's the bracing on my Cittern..

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In my opinion it does look a little on the heavy side- however now it's been strung up for eight months, the top hasn't shifted- and it's got great projection! After all, the instrument has five pairs of strings on it!

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kiwigeo
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Post by kiwigeo » Thu Oct 11, 2007 12:10 pm

Interesting tone bars Sam. Is the instrument a left hander?

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