Hi does any one have any idea how to fix a problem i have with my setup?

I have tried three amps, The third today brand new from maplins.  2 mixers, check cables cant rem how many times,  with the same result.

 I am getting a really low output on one chan.  When i slide the vol up on mixer, it sound like a distored state.  The only thing i have not change is the speaker.  It will be doing that next.  Does anyone think it could be the xover modules between speaker and horn.  Funny thing is both speakers seems to play ok from the working channel.  Its wierd.