After running a batch of 300-year-old Stradivarius violins through a sophisticated medical scanner, researchers say they may have figured out why the aged instruments are revered for their tone, clarity, and power: The wood used for the ancient violins shows a more consistent density than that found in modern violins, and researchers argue that this difference may affect how vibrations travel through the wood. In particular, the old wood shows less variation in density within growth rings, researchers say. Tree rings are comprised of a lighter, spongier portion that is produced during rapid spring growth and a darker, denser portion produced later in the year; in the Stradivarius wood these differences are less pronounced.