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The back is considered to work in two ways: Reflecting, or resonating

In order to have a resonating back at all time, I thought about doubling the back, meaning one back for the sound, invisible from the outside, and one visible:

How would you select those two pieces of timber? Would there be any difference in your choice? like taking the most quarter sawn and nice ringing for inside, and another, not as good for the outside? or do you think it is important to use two very nice sets?

what do you think about adding dome "soudhole" in the inside back?

Has anyone here done it? how did it go?is it worth it?

And how would you brace/radius each back?

What you suggest has been done many times by many different luthiers over time. Most recently and probably best known is the 'double tapa' or double-top (misnomer) by Manuel Contreras I & II. It is precisely what you are describing in that a separate back is suspended in the guitar in an attempt to improve the fundamental and provide a stiffer back.

Do some research on Contreras and his design and you will discover what has been done and his solution.

_________________
Peter

I asked a similar question a while ago, when I was thinking about building a 'double back' guitar. (Though I didn't pursue the building project, I still think it's an interesting idea.)
You may get some ideas from this thread:
http://www.delcamp.us/viewtopic.php?f=11&t=48931

Cheers
John

thank you