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Using tap tone to orient top joint?
http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=2532
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Author:  Michael McBroom [ Wed Jul 20, 2005 9:41 am ]
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Guys,

I have a well-seasoned set of redwood I'm about to join. It has excellent tap tone when I hold it with one edge up, but on one piece the tap tone is not nearly as good when I hold it with the opposite edge up. On the other piece, the differences are not as dramatic, but they're still noticeable.

This set is a little streaky, but it is very stiff, is perfectly quartersawn, and has tons of silk. The most obvious silk is about a third of the way out to one of the edges. When I hold this one piece so that the heavy silk area is toward the bottom, hence freer to respond to tapping, is when it sounds not so good. If I turn it around so I'm holding the wood just above the silk, it sounds loads better.

Here are a couple of shots of the set. The first one shows it oriented so the silkiest bands are toward the outside and the second one shows it so these bands are toward the center. The wood is pretty dark, but you should be able to see what I mean.





Because the set sounds best when I'm holding the wood closest to the silkiest areas, I am thinking that I should have these bands oriented to the outside (first photo). Does that seem to make a certain amount of sense, or am I over analyzing things?

Best,

Michael

Author:  LanceK [ Wed Jul 20, 2005 10:04 am ]
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Michael,
I think I would join it where the grain lines are the tightest regardless of how it taps. As for how it looks, I prefer the top orientation.

Author:  John Mayes [ Wed Jul 20, 2005 11:05 am ]
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I always put the stiffest section in the center.

I like the bottom orientation...I love dark streaky redwood...

Author:  Steve Kinnaird [ Wed Jul 20, 2005 1:43 pm ]
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You indeed might be over-analyzing things. When you glue those halves together, everything's gonna change anyway.

And man I hate to disagree w/ Lance, but I'm sold on the bottom orientation. That, to me, shows off your silking to best advantage.

(Sorry, Lance.... You can PM me and give me a sound thrashing.)

Author:  Michael McBroom [ Wed Jul 20, 2005 5:33 pm ]
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Guys,

The grain spacing is slightly uneven across the top surface, but it is somewhat tighter at the joint if the bottom configuration is used. The difference is minimal though -- like 60+ lpi compared to 50+ lpi.

I probably wouldn't have even raised the question, except for the tap tone with that orientation.

Good point about everything changing once it gets glued up.

Best,

Michael

Author:  Dave Rector [ Wed Jul 20, 2005 11:58 pm ]
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I have to agree with John and Steve. The arrangment in that bottom pic looks killer to me.

Author:  Alan Carruth [ Thu Jul 21, 2005 1:40 am ]
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The 'silking' is the medullary rays showing on the surface; evidence that those sections are perfectly quartered. Those will normally be the sections with the highest cross grain stiffness, since the rays 'tie the wood together' in the cross direction. That's _free stiffness_; you don't have to 'pay' for it with extra cross grain bracing. I'd put the better 'silk' toward the center joint, so as to get as much of it in the top as possible.

Tap tones can be misleading. You're holding the piece in a particular place and tapping it somewhere else. What you're hearing is all of the resonances that have a 'node' (stationary) line where you are holding, and an 'antinode' (moving area) where you're tapping. For the lower frequencies these nodes are 'supposed' to be nice straight lines in predictable places, but that assumes the wood structure is perfectly uniform, and yours isn't. I suspect the node you think you are holding has moved off at some angle, so that you are catching it more or less in the 'right' place on one side, but it's someplace else on the other side, so you miss it. Try moving your hloding point a little on the 'bad' side to see if the sound doesn't clear up. With redwood you really have to get that just right.

Author:  crazymanmichael [ Thu Jul 21, 2005 1:45 am ]
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as a matter of aesthetics, on an object like a guitar, i feel that attention is best centrally focused on the long axis. the orientation that has the silk central will tend to do this, whereas having the silk toward the perifery will tend to draw attention there, away from you beautiful rossette, bridge, inlaid fingerboard, etc.

Author:  Steve Kinnaird [ Thu Jul 21, 2005 1:48 am ]
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[QUOTE=crazymanmichael] as a matter of aesthetics, on an object like a guitar, i feel that attention is best centrally focused on the long axis. the orientation that has the silk central will tend to do this, whereas having the silk toward the perifery will tend to draw attention there, away from you beautiful rossette, bridge, inlaid fingerboard, etc.[/QUOTE]

Amen.

Author:  Michael McBroom [ Thu Jul 21, 2005 3:24 am ]
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Okay guys, you've convinced me. The bottom orientation it is.

Thanks again for your inputs.

Best,

Michael

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