If modern science can explain everything and recreate mystical legends, why are violins over 300 years old so sought after? If wood is so "dead" as you describe, these multi-million dollar instruments should be easy to reproduce. Wood is an organic material. Age, climate, vibrations, etc, all affect its properties. I like to think of a speaker cabinet as a sound box. Much like in a violin, it is designed to be stiff, yet resonant.
fyi, Pyrrho, string instrument players change their strings at least once every 3 months, so string wear and tear is not really a factor. Most of the sound is affected by vibrations.
This article may be of interest:
http://www.dalemfg.com/acousticaladjustment_021.htm
It shows how vibrations affects wood itself
I saw a show on PBS's Nova many years ago about why old violins sound different from new ones (it was probably the one entitled "
The Great Violin Mystery"). When people in Stradivarius' day made violins, like violin makers today, they tended to buy the wood that was available to them and varnishes that were available to them. In Stradivarius' day, wood was typically floated down rivers to be processed downstream, and could spend a good amount of time in the water. This differs significantly from the way wood is typically shipped to market today, where the wood spends less time (if any) in water. How the wood is treated afterwards was also different, as they used different methods of storage and dealing with parasites (woodworm, etc.). Additionally, the varnishes that were made back then were very different formulations from varnish that is typically made today. And the glues that hold the thing together are also different. All of those affect the wood and how it resonates. In other words, when a Stradivarius violin was new, it was quite different from a typical modern violin; this has absolutely nothing to do with age or "vibrations."
If a modern violin maker were to make two violins, one from wood processed like the wood Stradivarius used, and one processed like typical modern wood processing, and applied varnish and glue to the former that was like the varnish used by Stradivarius, with modern varnish and glue applied to the latter, but otherwise made the same, the two would sound different from each other. It has nothing whatsoever to do with age or "vibrations."
Now, like all material things, there are changes with age. Violins, like every other object, are subject to decay. So, over enough time, there will be changes, but they are not likely for the better. So, of course, old violins tend to be repaired from time to time, to restore them to their former glory.
Additionally, violins are very different from speaker cabinets, as speaker cabinets are typically made of mdf, not thin solid wood, and the speaker cabinet is designed to resonate as little as possible (within the confines of the price and other objectives of the speaker). You are just wrong about what a speaker cabinet is supposed to do; it is not a soundbox (in the sense in which the hollow chamber of a violin or other stringed instrument is a soundbox); it is supposed to be completely inert and lack vibrations altogether. This is why a dense material, mdf, is selected, and why it is much thicker than the walls of a violin. A violin is supposed to resonate, but a speaker cabinet is not supposed to vibrate or resonate at all. So the two things are quite different, and it is absolutely ridiculous to pretend that the one is a good analogy for the other for most purposes. One is made to resonate, the other is made to not resonate. One is made of thin solid wood, the other is made of thick mdf.
Both, however, are subject to decay and destruction, and in those ways, they are alike, but no more so than any other two man-made objects.
As for the price, one is antique, and the other is new. Also, there are no new Stradivarius' being made, so the supply is limited. Price is largely determined by supply and demand, and it makes no difference whether that demand is reasonable or not.
There are other issues as well, as Stradivarius was good at marketing:
"Stradivary was a good salesman. He sold to kings and those instruments were well kept. His neighbors made good violins too, but they sold to musicians and were used up," Nagyvary said. "But everyone in Cremona made good violins because they used the same process of smoking or boiling the wood to kill wood worm.
"The violin trade doesn't like a scientist figuring out something simple like that," the biochemist said. "I think the comparison test is worthwhile. I wouldn't take a chance to stick my neck out otherwise."
And also, in blind listening, Stradivarius instruments do not sound any better than others that are properly made:
http://en.wikipedia.org/wiki/Stradivarius#Controversy_over_sound_quality