just to get the sentence here:
"The average human yells at about 80 decibels, which carries along with it about .001 watts of energy..."
Since it "carries" it along with it 0.001 watts, that is all that is there, in the air. There is no way to put 50 watts to a speaker and have it all go to a glass of water or similar. First of all, you will lose most of the power in the speaker, largely to heat, etc. I don't know how to do the math, nor do I want to go find out, but judging by the 0.001 watts from 80dB, say a very good case scenario you have enough power in the sound waves to be considered a full watt. Now focus this at a glass of water. Can you still hear the speaker? Yes, so not all of it is going to the water. Considering how well sound bounces off large bodies of water, almost none of it gets absorbed I would guess. Even if you did get that full watt into it, using their math, it would take 52000 seconds to heat your "coffee" or whatever. (well over half a day) since this is way longer than the rate at which it would loose heat, etc.
However, feel free to try it.
Especially the second one, that sounds fun if it works.