The PB12 has a bump in the frequency response around 50 - 60hz, which I found a little annoying as it made the sub sound more like a car subwoofer. The EP500 has DSP that smoothes out the frequency response for a linear/flat playback, just nice and smooth sound reproduction through the range. The DSP also limits the output making port noise nearly nonexistant on the 500,
_________________________
Jason
-----------------
TTTHHHPPPPPTTTT!

My HT