When I posted this, a
heated and
agitated discussion was not what I had in mind.
Just offering a plausible explanation for what so many of us observe about old and "played-in" instruments. As subtle as the effects would be I don't think one instance of extreme heat exposure or extended playing would mimic true aging. It is possible to add so much heat that the whole natural aging process is wrecked in favor of reactions that only proceed at the higher temperatures. I'd think dehydrating the bass would remove a good deal of the moisture that is one of the necessary vehicles in the wood for acid / base reactions to happen. That is why kiln drying arrests the normal drying / aging process and these woods are not as good for tone wood, but are softer and more desirable for carving into other things that are not musical instruments. Wood carvers prefer kiln dried wood, musical instrument makers usually do not. And the kiln dried stuff is reputedly softer.
I wouldn't recommend any
extreme measures to accelerate the aging of an instrument made from relatively new wood. Hooking it up to a jack-hammer or leaving it in the car in full sun are certainly not good ideas.
Normal seasonal changes with the wood taking up moisture and releasing it and regular playing is probably the safest practice. But I do think it is desirable for builders to use wood that is as old as they can possibly obtain because aged wood is aged wood, regardless of when it was carved into a bass. In fact, the heart wood in a live tree is actually dead already, and is much more aged than the outer tree rings even when a tree is harvested. That part of a tree, the old dead wood in the center, is structural support for the living outer part of the tree. It is biologically adaptive for the tree to have stronger aged dead wood in the center. That way it can get taller, withstand the higher winds, and get the best light for photosynthesis.
It is a shame to me that we are losing the best American spruce for future musical instruments to the timber / lumber export market.