I installed new speakers in my car recently, and could tell something was just "off." I did some research on my own, and concluded it was most likely a polarity issue with the speakers. I didnt want to buy an expensive polarity testing device, so I looked through the App Store store and found this app. Trust me, it works. In less than 5 minutes, I installed the app, hooked up my phone to the car stereo, and tested all 4 car speakers individually. The test showed me 3 out of 4 speakers were connected properly with a positive polarity. I switched the wires for the one that came back negative, and re-tested it. Everything was positive and the music sounded full again. :-)
To The Devs: Thanks for taking the time to make this stand-alone app, it really helped.
RewindTheImage about Speaker Polarity, v2.5