So if I play a Memorex tape of Ella Fitzgerald in a crystal shop, and no one else is around, the glasses won't break because there is no sound? Not sure I agree.
First of all, if your wife didn't hear you, then of course you exist, because there has to be a "you" for her not to hear...
But more importantly, this is the most common deffinition of "sound" taken from the American Heritage Dictionary:
sound (sound) n. 1.a. Vibrations transmitted through an elastic material or a solid, liquid, or gas, with frequencies in the approximate range of 20 to 20,000 hertz, capable of being detected by human organs of hearing.
So yes, there is sound, as long as someone is "capable" of hearing it. But if no one is capable, is there sound?