dull sound

i have a set of mordaunt short speakers which i absolutly love but i noticed when playing music that the sound was really dull like there is no mid range .i tried different music to see if it was that and it wasnt .i checked the connections into the amp and all was ok .i even went out and brought new bi wire and still i was getting the same sound ,i then resorted to trying my surround sound speakers to see if it was maybe the amp and they sounded perfect ,which means there must be something wrong with my speakers.does anyone have any idea as to what could be the problem and can it be fixed