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Recently when I thicknessed a sitka flat top for a J200 type guitar I used a method of assessing the top stiffness, learned as described by several builders, where I shook the top and observed how floppy it was and listened to the "wap wap wap" similar to sheet metal.

Would this work for thicknessing the back as well? Would there be some level of "wap wap wap" at an appropriate thickness?

I ask because I am thicknessing a maple back and while it seems a reasonable thickness, and stiffness, I'm not noticing a sound like I do with the top.

I think that depends a lot on if you build with backs that are sympathetic or ones that are reflective. Reflective backs should be fairly stiff and their tonal properties do not matter as much. Sympathetic backs should be tuned to a frequency that compliments the top but does not allow them to synchronize vibrations.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Thanks Brian, that makes sense.