I disagree with those who said anything above 600 doesnt make a big difference.From my experience, it does. I ran my 2500d at 4 ohms and it was loud, but then I ran it at 1 ohm and it got a LOT louder... But I have only had them for a week or two, Im gonna wire them back down to 4 ohms and play around with them. And my gain is only 1/4 up, my HU is 4.5v pre-out but my voltage drops bad... 225 amp alt on the way //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif