Subject: How do intercoms work?

We were talking about sound, and how our ears work.  Then we talked about sound 
waves. Then we asked "How do intercoms work?"  Our hypothesis was that they 
work like a tin can string telephone, funneling sound into the speaker and 
running the sound through the wire and coming out the other side.  But we might 
be wrong!  We were proud of ourselves for observing, asking questions, and then 
coming up with a hypothesis but we did not know how to create an experiment 
that would let us figure out the answer.  We did look on-line but only saw 
companies selling intercoms!  Thank you for answering our question. You guys 
rock!

Re: How do intercoms work?