• The tiny factory-fitted 4" speakers in a 70 Series are mounted underneath the dash, firing down towards your feet.  Larger 6" speakers in the doors with custom mounts are simply better, and the tweeters give us more control over where the sound appears to come from (higher up closer to your ears instead of somewhere below the knee).
  
  
• The sound deadening helps reduce acoustic loss.  The door acts as a speaker enclosure, and as the door skin vibrates, the energy turned into sound gets lost as vibration instead.
  
• The micro amp drives those new speakers.  The head unit, either the factory Toyota or an upgraded unit simply doesn't have enough power to make the most of the speaker upgrade.  The amp delivers the power they need so that it sounds great WITHOUT pushing the head unit too much.

• The slim sub fits under the driver's seat.  It produces the perfect amount of bass so that you know it's there, but it's not going to set off car alarms or upset the neighbours.   Plus, like the amp it's invisible - nobody will smash your window to steal it.

Brands involved:

Key items in this system may include Alpine Status, ZeroFlex, Hertz, Zapco, Harmony, JL Audio, ESB, Sony ES, Rainbow, Audison, and Focal, among others.