[Aidevah]

It should be mentioned that "old" violins that are still used today have all been substantially rebuilt to accommodate later repertories. There is a lot of difference between an early Baroque violin and a late 19th century violin including the fingerboard and the type of strings, and only a few museum strads that have not been played have retained their original configuration. One benefit of the early music movement that took off in the second half of the 20th century was realising that the "old" and "original" instruments weren't actually that old or original after all, and new baroque violins had to be made from scratch to attempt to reproduce what they would have sounded back like in the 17th and 18th centuries.

[koverstreet]

It's more than that - the bass bar on modern instruments is substantially heavier, because string tension with modern wire wound strings is higher than baroque era gut strings; the older instruments are more lightly built.

The tone you get with gut strings is completely different than with modern strings - more complex, more resonances, but a modern style instrument will deaden that somewhat, you really want a period instrument to take advantage of gut strings.

https://www.youtube.com/watch?v=7y4lcQ7BTLw

The neck is also different, but that affects reaching the high end of the fingerboard more than accoustics.