The sound system. The head unit is a Sony ES-650 powered by a Sony XM-5046 four channel amp. The front speakers in the Q-Forms are Polk DX-3055 five and a quarter inch with one inch tweeters. The rear speakers are Polk 6x9 two way speakers. I used a ten inch Polk sub woofer powered by a Premier GM-X632 amp. Not the best system in the world, but not to shabby.