problem with my new 6x9 car speakers (polk audio).?

[Eduard]

Ok so i recently bought polk audio 6x9 speakers type db691. they are 300w peak each. So when i got them i opened my package and took 1 speaker to my car to test it. I plug it in and turn on my car, and to my dissapointment i could barley hear anything comming from the back. I got db651 polk audio 6.5 in my doors that sound awesome. these 6.5 sounded better then the 6x9 even though they are the same brand and model. So i came home and let my brother know. he took out his 6x9 in the back of his car and put mine in there place. Then he messed with his deck and adjusted the settings to only play my 6x9's and added a bit bass boost. What do you know, bad quality again. He turned them up high and they sounded like $10 broken speakers. He then switched the wires around. he put - wire on + speaker visa versa. The quality sunded much better, more cear. He turned the volume up this time and the speakers handled it well. My question is, is this normal? Is it safe for my speakers to run them like this? Were the speakers + and - reversed at the factory by accident or is this normal? I dont want to go through the hasstle of returning these speakers as i got them through amazon. But at the same time i dont want to keep them if they are somehow defective. Can anyone help me? Any help is appreciated =]