My speakers don't play words, only sounds?

my computer is hooked up to big speakers. when i play music on my itunes, the speakers play the music and melody, but no words are emitted. the words are very soft and almost sond like echos.the melody on the other hand is pretty clear. what could be wrong? its not an itunes problem because i tried playing different songs on windows media player and youtube, and the same probem is happening. i also changed the computers equalizer settings and this is still happening. what should i do? this is driving me nuts! thank you