The best way to install and amp/speaker(or amp/sub) combination is to find a sub/speaker you want and see what the manufacturer suggests to power it. Use a speaker and amp of the same brand and same RMS power NOT PEAK which many speakers and subs are measured in. There are only probably half a dozen manufacturers that rate their equipment in RMS all the others are in peak. Also look at what the ohms rating is. If the sub is rated at 2 ohms, power it at that. That way will give u the best performance and sound quality. Ill give you an example, a set of Roadmaster speakers you can buy at walmart for around 20 bucks. The box says 100 watts, well they are only rated at 10 watts RMS at 16 ohms. Now thats a big difference and there isn't one car stereo or amp around that i know of that will power anything at 16 ohms. Regular speakers are usually 8 sometimes 4 ohms and subs usually from 8 down to 1. (Rockford makes an amp that is stable down to .5 ohms)