What if the back is louder than the top when tapped?

[Herman]

Maybe a question for John P. or R.M.Mottola.
I'm reconstruction a Cocobolo Jumbo with a new top. The top is still a bit on the thick side (2.8mm, 0.11")
When I make a spectrum analysis of just the body (no neck, no bridge), when tapping the top the back resonance is significant louder than the top.
I never saw this before.
What to think about that?
Herman

[John Parchem]

When I look at that graph I suspect 190 is the top. The back looks to be higher. Try tapping the back and see if you can better pull out the back.

[Herman]

When tapping the back:


And tapping the top with damping the back:

[John Parchem]

Hard to tell. Two different thoughts. You back and top are close to each other or the back is around 260 Hz. Top still close to 190. With a bridge it will end up around 180 Hz. Another trick if you have some blue tack putty is to put 30-50 grams of it near the bridge position. It will mostly just drop the top peak. That will help identify the top peak.

One other thought is to drop the gain of the input (microphone) as the extra peaks might be from clipping.

[Herman]

This is tapping the back with damping the top:

[John Parchem]

Your back and top are close to each other thus the double peak. When the bridge and strings are installed the top will be lower than the back. Maybe 180 top and 190 back

[Herman]

Thanks John, I want them to further apart. I will stiffen the back with 2 extra braces. And I will loosen the top a bit at the perimeter, 'cause that is still a bit too stiff to my taste.
If I get there, I will post a pic.
Herman