Turning a Speaker into a Microphone

What happens when you connect an XLR cable to a speaker and plug it into a mixer or mic pre-amp?  It simply becomes a microphone!  As a fun project, we took an old speaker from a cabinet and did just that. The best use that I've heard of for this type of microphone is its use on a kick drum to capture the extended low-end.  These are sometimes referred to as a "sub-kick".  We are hoping to find a more professional way to mount the speaker, but for now we have something usable to work with.  It will be interesting to see the results when Paul tests it on a drum kit this weekend.  Here's what we made: