Case-Method

The website for the Academy of Music in Philadelphia states that it is the "oldest known opera house still used to house operatic performances." I agree that that is true specifically for the USA. But in the whole world, is there really no opera house built before 1857 that is still used for opera?

I've read reviews of performances and recordings in which critics complain about a singer's "dry tone." Could any of my fellow opera lovers help me out by explaining what that means?