Well, I'm a saxophonist, a double-bass player, and a mechanical engineer.
I have heard many arguments that the saxophone's body is somehow vibrationally involved in tone production - materials, finishes, cryogenic treatment, add-on weights, etc., etc., etc., etc. Not one person making these claims has ever, in my experience, presented valid data in which the very basic standard of double blind testing has been followed - only anecdotal reports. Furthermore, of the few who actually bother to posit a mechanism for these supposed effects, I have not seen any such purported mechanism that doesn't violate what is well known about materials science, acoustics of woodwind instruments, or the behavior of materials in vibrations. (By the way, the materials science of metals and the behavior of mechanical items in vibration are two of the most comprehensively studied subjects in all of engineering - bascially all of the Industrial Revolution depends on these.) Rather, every experiment I've ever read about, that was conducted in a valid way, has indicated that the vibrations of the walls of the saxophone have an undetectable effect on its tone or response.
So I'm going to retain my opinion, that the preponderance of evidence is that the material of the walls of the saxophone is irrelevant to its performance - thus, all arguments about "vibration aging", cryogenic treatment, material's effect on sound, plating or lacquer's effect on sound, adding weights to the outside, etc., etc., etc., have no physical validity and any effects are psychological.
The double bass, as guitars, violins, and many other stringed instruments, DOES get its sound directly from the vibration of the body, which is set into vibration by the strings, and then sets into vibration the air volume within the body. Furthermore, the resulting sound is then transmitted to the listener by a combination of transmitted pressure from sound hole(s), and the external surfaces of the instrument exciting sound vibrations external to the instrument. In the case of such instruments, there is absolutely no argument that the vibration of the wooden box makes a very significant contribution of the sound; and furthermore there is extensive knowledge, backed by test data, on the effects of altering the response of the wooden box (make the plates thinner, make them thicker, change bracing patterns, etc.)
The operating principle of a stringed instrument as guitar, violin family, mandolin, etc., is DIFFERENT than the operating principle of a woodwind instrument.
So now we come to the question - does the tonal behavior of a double-bass change over time, without reference to the player, and due to changes in the wood? As opposed to, for example, bridge feet gradually sinking into the top plate and having an increased contact area (or many other things we could theorize)
Secondary question would be, what kind of changes and what causes them? Is it ongoing repeated vibration, is it the natural aging process of the wood, some other things? How important is each of these factors?
As I noted above, I am at present agnostic on whether there are actual changes in the wood that affect tone, and if that's demonstrated, I'm agnostic as to the effects of playing vibrations. I simply haven't seen enough data to form an opinion. The one thing that raises questions in my investigator's mind is that the changes are always reported as positive. It seems to me that if there are actual tonal effects due to these changes, there would occasionally be reported negative changes.
I will say that if these mechanisms DO exist, and playing vibrations and wood aging do make differences in tone (and I am open to this being the case) - such mechanisms will be secular, resulting from actual physical causes, and not requiring supernatural intervention.
