Let me ellaborate a little deeper. Normall in car audio there is the CLASS D, and the CLASS A/B. Class A/B used a type of topology that in the end result give you great sound quality, but low efficiency(around the 50% depending on amp). They are considered to a little rougher on youre cars electrical system. Because of there great sound quality they are used for speakers or subs. A class D amp uses a difirent topology that in the end gives you horrible sound quality, is not able to play the whole audio spectrum, and causes lots of distortion BUT that is only when you start getting into the upper mid bass and over into the mid range. They are highly effiecietn(around the 80% depending on amp) and are easier on the cars electrical system and very affordable watt per watt/ per dollar. So generally most people with subs have them crossover at 120hz( i reccomend much lower , but most idiot installer dont know why) so generally youre subs are not going to be playing much over 200hz(they shoulnt any ways, thats too high). So in those areas of the musical spectrum the distortion is minimal, and cant be heard any ways because its bass. So you end up with a sonicly enfirior(typically, just picked up a alpine pdx 150.2 for my components, depending on the engineering.) amp, that works great for bass!