Radio Speaker output?

Hi all. Anyone know what type of signal I should expect at a Radio Speaker? or what tests to use to determine if a speaker is bad? I have one at the shop that only one speaker works. I had one last week that both rear speakers did not work, for that one I took the radio out and switched the speaker wires around to troubleshoot it. I'm sure there is an easier way. I have this one (08 Acadia ) for a few days. so I have some time anyway. Thanks ahead of time.

Well, I answered my own Question. I tested a known good speaker and I got a DC volt wave form that reverses polarity very quickly. The voltage increases as the volume is turned up. Seems to be about 4 volts at a normal volume and close to battery voltage at max. The l/r speaker is bad for sure. I suspect they are all bad. I'll test those tomorrow. I'll post a wave pic at normal volume. 4v scale/ 30 sec ). In case anyone ever needs to know this.

Good work! I've used my scope to diag raidio complaints and was going to suggest you try it, but you beat me to it!