Ok have ssingle sa x12 d4 says 1250 rms. Got hifonics Brutus 4000.1 says it does 2000 rms at 2 ohm. My alt does 140 amp. Door speakers pull 1200 watts haven't got an amp for them yet. But before I spend more money. What are my power concerns?
best approach is to invest in a cig lighter voltmeter and monitor voltage after you install. if the voltage drops below 13.5V while driving then the alt cannot keep up and you need to consider some upgrades to the wiring and maybe components.
Door speakers don't "pull" wattage. speakers present an impedance load that the amplifer is trying to drive. as input signal (audio/RCA) increases, the voltage out of the amp increases. as voltage increases the current out of the amp increases. wattage delivered to speakers/subs from the amp(s) depends on the volume level. music is fairly dynamic and has a pretty low signal for most of the time.