i have an alpine CDE-9843 HU and i have 8 speakers hooked up to it and when the bass in the song hits the lights in the HU go dim and when the bass stops the lights go back. do i need an amp for some of my spaakers? on 1 rear speaker out there is 2 45 watts max 6x9's one is a three way and the other os 2 way, and one 4 inch that is stock, i dont know how many watts, but on 1 of my 6x9's its only 1 way because the tweeters got broke off. 2 of my 6x9's are alpine and the other 2 are stock out of a '93 buick regal. i have to 6,1/2 inch speakers in the dash they are 2 way pioneer speakers i doubt these are any more that 30 watts.is an amp for the rear necessary?
Eight speakers? You'll definitely need an external amp. The headunit cannot handle more than four speakers-otherwise your system will suffer from poor sound quality and there is a high risk of damaging the headunit.