Audio Systems: Speaker with weak response, inch speakers, gold connectors

Question
I have a pair of Polk RT-800 speakers. One speaker is significantly weaker, especially in bass response, than the other. The cabinet includes two 6 1/2 inch speakers and a tweeter. As far as I can tell, all three are working, they're just weak (especially noticeable in bass, but also weaker in midrange). I've checked the polarity of my speaker connections. I've swapped the left and right speaker positions (that's how I figured out it was the speakers and not the amplifier or connections). The speaker has two sets of connections on the back with gold connectors to join them (a set-up to allow bi-wiring or bi-amping). The connectors are in place. I tried both sets of connections. Nothing has made a difference.

The speakers all look great from the outside and I don't hear any distortion or rattling.

I'd like to fix this or have someone else do it. Is it likely to be a very expensive repair? Do you have any idea what the problem might be?

Answer
Depending upon what the actual speaker drivers are within the cabinet, you may have a case where the coils are faulty.  This is a difficult one to diagnose without hearing the problem.  Make sure that the 2 6" drivers are not out of phase (polarity correct).  Did this just happen all of a sudden?  There should be a crossover built into the cabinet that may have a problem as well.
Dan