This is less a question and more a relation of a story. I was in my local store today when come guy brings in his 8x10" ampeg cab and says that one of the speakers has blown. I was speaking to him and the dude at the store plugged it in and had a play through it, being an 8x10 it was hard to tell which one was blown without pressing your ear up against the speakers. The guy at the store went to press his face up against it when the bloke who brought in the cab stopped him. He said he had a better way. He pulled out a small tuner/metronome and plugged it into the rig. then reached round the back and started fiddling with something. This guy had installed switches for each of the speakers individually, and using the metronome he was able to discover which speaker was busted. I know it's hard to explain but I thought is was a good idea, practical but a bit dangerous. Anywho, thats my story.