do you need to hook up crossovers for subs? i was going to use a ported box for my 2 12" r's, but at this site it said to use a crossover to prevent any damage to them if they distort.
You need a lowpass filter for a subwoofer. If it's in a ported box then you'll also need a highpass filter. Most amps have filters on them, as well as headunits.