Some interesting inside baseball for ya...
On my cornerless bass that I just finished I made the top first and then wanted a hybrid bracing for the flat back. I designed my own to spread out the stiffness with an X-brace with the intersection at the soundpost. This is not anything new, many makers have done an X but mine was different because it is braced similar to a flat top guitar that CF Martin designed. An X with lower fan type braces. The reason was for the braces to hold the back into a slight dome shape with minimal weight. I thought this might make it behave similar to a carved back. And not have the cross grain situation of the flat back with its cracking problems.
Since I was shooting in the dark I tap tuned it, removing wood from the braces to make its stiffness similar to the top. The X back did have nice ringing tap tone that was close to the top's. It was about a tone higher. After stringing, it did have a pretty strong wolf at open A. I was kind of expecting that and was able to move it a little as to not interfere with bowing by using a brass weight on the afterlength.
The bass seems to have a pretty nice smooth round sound that is a little different from the typical flat back to my ear. As for long term stability, I am certain that I have done a positive thing by not gluing 3 or 4 braces straight across the full 27 inch width of the back. So now the wood can expand and contract across the grain freely as well as flatten the dome when it gets dry. I will know if a few seasons just how beneficial this was but have already noticed the back going flat during dry spells. I also notice the post getting looser and tighter with this.
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