I'm currently taking the free online course from Berklee College of Music called "Intro to Music Production".  This week had an assignment list of a whole bunch of different topics.  I chose one from the list which was to demonstrate comb filtering in an acoustic environment and prove that the comb filtering is taking place.

Should you be interested:

http://www.youtube.com/watch?v=0IV7YAoIGAg&feature=youtu.be

audio capture of the experiment at this SoundCloud link:

http://snd.sc/1d1zBKh

I've never proven to myself that this comb filtering takes place.  I spent way too many hours working on this tonight, but I'm convinced that all of those people that say that putting monitors on the meter bridge of a mixing console is a bad idea - well, I would now emphatically agree with them.