Famous fact

Here's an answer from snopes.com:
http://www.snopes.com/critters/wild/duckecho.htm

 

I agree. This is a myth. The link provided by robphy says it all.

 

If a quacking duck were to emit a single acoustic phonon, it may reflect off of
a wall or it may get abosrbed by the wall. And no one knows why since no one
knows the physical basis of quantum superposition.

So parts of a duck's quack somtimes make an echo- and no one does know why!

 

As much as I am not a fan of the show, but Mythbusters had a segment on this as well. They had an accoustic pro come in with a spectrum analyzer and looked at the quakck in various scenarios. Their pro came to the same conclusion as the referenced article from Snopes.