If you move the sound hole too far back, the instrument begins to sound more like a trumpet than a guitar.
Just kidding. Shouldn't make a bit of difference.
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| Modifying Bracing http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=40948 |
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| Author: | WindyCityBluesBox [ Mon Jul 22, 2013 3:12 pm ] |
| Post subject: | Modifying Bracing |
Hey guys. Im building a j-185 right now, but Im extending the scale length to 25.5 and Im making it a 12 fret join to bring the bridge farther into the lower bout. This means I need to change the brace locations/positions. In order to have the X-brace properly positioned under the bridge, I either need to shift the bracing backwards about an inch and a half, or I need to change the angle of the x-brace. What do you guys recommend? -Alex ? |
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| Author: | meddlingfool [ Mon Jul 22, 2013 4:25 pm ] |
| Post subject: | Re: Modifying Bracing |
Move the x's... |
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| Author: | meddlingfool [ Mon Jul 22, 2013 4:26 pm ] |
| Post subject: | Re: Modifying Bracing |
Possibly shift your sound hole as well... |
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| Author: | Rodger Knox [ Mon Jul 22, 2013 4:34 pm ] |
| Post subject: | Re: Modifying Bracing |
What's the angle on the X? If it's more than 90°, I'd consider reducing it a little & not shifting as much. |
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| Author: | Greg B [ Mon Jul 22, 2013 10:10 pm ] |
| Post subject: | Re: Modifying Bracing |
When I made a 12 fret J200, I added about 1/2" to the upper bout, and slid the X back the remainder of the distance. Worked for me, and I think the shape looks well balanced, like the earlier 12 fret version of that 'Jumbo' body shape. |
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| Author: | WindyCityBluesBox [ Tue Jul 23, 2013 7:48 am ] |
| Post subject: | Re: Modifying Bracing |
I actually started drawing p some new plans with the x-brace slide back, but the modification left the soundhole too far away from the brace. Would I be safe by sliding the soundhole back with the x-brace? If that wont have any negative structural/tonal properties then I think im good to go! |
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| Author: | Tony_in_NYC [ Tue Jul 23, 2013 8:02 am ] |
| Post subject: | Re: Modifying Bracing |
If you move the sound hole too far back, the instrument begins to sound more like a trumpet than a guitar. Just kidding. Shouldn't make a bit of difference. |
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| Author: | Rodger Knox [ Tue Jul 23, 2013 10:55 am ] |
| Post subject: | Re: Modifying Bracing |
I believe moving the soundhole back will affect the main air resonance, but I'll let someone that knows how it will affect it confirm that. |
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| Author: | Jim Watts [ Tue Jul 23, 2013 11:58 am ] |
| Post subject: | Re: Modifying Bracing |
Roger, why does moving the sound hole effect the main air? The box volume stays the same and the hole diameter is the same. |
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| Author: | Rodger Knox [ Tue Jul 23, 2013 1:34 pm ] |
| Post subject: | Re: Modifying Bracing |
Jim Watts wrote: Rodger, why does moving the sound hole affect the main air? The box volume stays the same and the hole diameter is the same. I don't know, but I found this post by someone that does: It occurred to me that William Allen might have said something about this in his article on air resonances in American Lutherie #1, so I dug it out. Nope. He does have a lot of interesting stuff, though, such as a discussion of how the sound hole location changes the Helmholtz resonance. Nothing's ever simple.... Al Carruth |
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| Author: | Greg B [ Tue Jul 23, 2013 2:56 pm ] |
| Post subject: | Re: Modifying Bracing |
This is a gross simplification: It is because an enclosed body of air will exhibit not only Helmholtz resonance, but also pipe resonances. It's a little counter intuitive because a guitar body is not shaped like a pipe, but still they are there. Imagine waves bouncing around in a small enclosed pool. Anyway, as the exit (soundhole) gets closer to the end of the 'pipe', the output tends to increase in magnitude slightly. Also, the phase characteristics change. Practically speaking, moving the soundhole an inch or two one way or the other is not likely to give you 'more bass', but it may change the frequency response slightly due to phase differences between the spectral response coming from the sound hole, and the output from the top resonances. This might be audible if you have good ears. |
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