THERE IS NO FREQUENCY SPECTRUM ON A PASSIVE SPEAKER, BECAUSE IT IS NOT A WIRED SPEAKER. THE BASS IS PRODUCED BY THOSE SPEAKERS THAT ARE NOT PASSIVE LIKE YOUR MID RANGE. THE MOVEMENT OF THE NON PASSIVE SPEAKERS CREATE AIR PRESSURE INSIDE THE SPEAKER CABINET  THAT MOVES THOUGH THE PASSIVE SPEAKER. YOU HAVE VERY LITTLE CONTROL OF THE BASS RESPONSE IN YOUR SPEAKERS.