OK, I finally have to ask. I'm tone deft, don't play the radio loud, and one speaker seems to have the same sound as 12. So I'm trying to figure out what I have in my vehicle a 07. I've got 2 front and 2 rear speakers in the doors and one sub? behind the rear seat. I changed the stock radio to a AVIC D3. Do the door speakers have a amp or are they run by the head unit? I know from hooking it up that the the sub must have a amp of its own because the D3 has a power lead that must be hooked up to it. However, it doesn't deliver enough power to run the sub so does the sub have it's own power lead. With the stock unit and the D3 I have never heard any sound from the sub.