Speaker Troubleshooting/Suggestions

Hello all! This is my first post in the forums!

I tried to find information on speaker replacement/troubleshooting and came up short for the problem I'm encountering.

I bought a 2009 Package 2 about a month ago with 92k on it. I discovered that both rear speakers and the front lower right door speaker did not work (I played around with the audio settings and couldn't get any sound out of them). However, the front lower left speaker and both front, upper small speakers worked. On my way to work this morning, the lower left speaker also lost power (no audio whatsoever). All that's working at the moment are the 2 front upper speakers...no bass or sound coming from any of the lower door speakers. I'm not that familiar with audio systems, but I'm open to trying to problem solve before going to a dealership. Just not sure what the first step would be at this point. It seems as though all 4 speakers need to be replaced, but I'd like to know if there's a way to troubleshoot before buying the new speakers. Any help is greatly appreciated!

Also forgot to mention that I do not have the JBL system in my Prius, just the basic system as far as I'm aware.

 

Thanks for the tips! I think I'll start with that and hope it's just faulty speakers

Will update once they've been tested