Sound is propagated by waves. Waves can interfere.

Suppose there are two tenors standing next to each other and each singing a continuous middle-C.

1. Will it be the case that some people in the audience cannot hear them because of interference?

2. How does this generalise to an array of n tenors?

3. Given a whole choir, to what extent are their voices less than simply additive because of this? Is it possible that, for some unfortunate member of the audience, the choir appears to be completely silent?