Diagnose electrical problems by chasing voltage drops, instead of the old-fashioned way -- checking continuity. Including Mike Allen's Physics 101 introduction to Ohm's law.

On the other hand, if you check a suspected defective fuse or broken light switch, you’ll probably get an Ohm reading other than zero. That may indicate a blown fuse or broken light switch.

Ohm is the unit of electrical resistance. Just kidding. Well, it is, but this is how it's of most relevance to amplifying sound. Speakers have at least one, and usually several, drivers.