its not idling alternator 
i meant to say that....jab gari start ho aur around 800rpm pe ho to its in idle mode right! thats to say the engine is idling....
at that rpm the alternator produces max 10-15amps. trying to max out your woofers while engine idles at 800-1000rpm will result in voltage drop when amp tries to draw the required amps....
so revv the engine upto 2500-3000rpms when you're trying to max out your subs, and see if it improves anything 
