Soundman Trick: Checking a speaker with a 9V battery

Here's a soundman trick to check your speakers with a 9V battery:

Take a speaker cable, hopefully with a banana type connector at one end.
Plug in your speaker.
Take the 9V and touch it across the leads.
You should see the speakers pop out or in.

This will tell you if the speakers are getting signal, and that they are in phase. Out of phase speakers will go one in, one out.

Hope this helps (especially after the 10PM set and you know something is blown!)