How to tap the coupled top and back

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JamesO
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How to tap the coupled top and back

Post by JamesO » Tue Nov 29, 2016 12:52 pm

I have another Gore-method noobie question, guys. I'm ready to pore fill my current build and start the finish process. I've left the brace that spans the lower bout full height, and I'd like to begin the testing process so that I can sand in the notch and tune it appropriately.

The Technical Note on Collecting Spectrographic Data in Design Appendix I says to hold the in the playing position and tap the mallet across the saddle area. I assume this is for measuring the top. Do I flip the guitar over to tap the back in order to collect the back's data? Do I muffle the back while I'm tapping the top? Do I muffle the top while I'm testing the back?

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Trevor Gore
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Re: How to tap the coupled top and back

Post by Trevor Gore » Tue Nov 29, 2016 7:16 pm

I'm assuming the body has no neck and no bridge.

Tap the top, without damping anything, and look for the T(1,1)1, T(1,1)2 and T(1,1)3. The T(1,1) will move a bit and the T(1,1)2 will move quite a lot when the bridge and neck go on, but you need to measure these so you can figure out how much these will change on your guitars when you add the bridge.

Flip the guitar, and without damping anything, tap the back. This will give you the B(1,1), which will be slightly lower in frequency than the T(1,1)3 (if you can see a T(1,1)3).

Guestimate your target T(1,1)2, then add four semitones and that is your target T(1,1)3. Shave the back brace until the B(1,1) frequency approaches the target T(1,1)3 then leave it there until you get the bridge and strings on, then proceed to dial it in from there.

Target frequencies for different guitar types are given in Design Appendix V (1st Ed) or VI (2nd Ed).

JamesO
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Re: How to tap the coupled top and back

Post by JamesO » Wed Nov 30, 2016 2:27 am

Fantastic. Thanks, Trevor. :cl

I see the targets in the book. Should I aim for those targets without the neck and bridge on, or with the neck and bridge on? I had assumed that I should have the neck and bridge on.

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Trevor Gore
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Re: How to tap the coupled top and back

Post by Trevor Gore » Wed Nov 30, 2016 9:05 am

The targets in Appendix V (1st ed) or VI (2nd ed) are for finished, strung instruments.

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