i have a 1997 mustang convertible, i replaced the head unit, inside speakers and added 2 12'' subs, there is one amp for the subs and i have two three way speakers and two two way speakers on the inside, the bass really kicks and sounds good but when i turn up the music the vocals sound terrible, what can i do to fix the distortion? should i get another amp for just the speakers? or is there somthing im missing?