Although not a violinist, I've followed with interest the discussions on the manufacturing process on the quality of sound of violins (C&EN, Feb. 2, page 29, and May 4, page 4). Several years ago, I heard a series of syndicated radio broadcasts by Karl Haas on the comparison of Stradivari and Guarneri violins. The same violinist played the opening solo phrase of Max Bruch's violin concerto on a variety of Strads and Guarneri instruments. Regardless of the performing artist, I've always thought that the sound from a Strad was a little dull, lifeless, and even flat. These recorded comparisons confirmed my independently formed opinions.
Years ago, Joseph Nagyvary gave a presentation at a meeting of the ACS Chicago Section during which he elaborated on the chemistry of the Cremona violin crafting processes. He also presented audiogram data of how the sound of Strads is deficient in higher harmonics, leading to a diminished brilliance of sound.
I agree with Thomas Zebovitz that ultimately the quality of sound from any violin is mostly dependent on the talent of the performer and that modern instruments shouldn't be discounted out of hand, but I'm convinced that the Cremona sound is remarkable after all of these years and that good to great violinists can achieve an even more remarkable sound with a Guarneri. Unfortunately, there aren't very many of them around compared with Strads for reasons detailed by Nagyvary.