This is the Second Series, although called 15 without a series number, chalk and cheese to the earlier models. These have more powerful bass amplifier inside the module, giving far greater bass response and much greater control over the levels. The cube speakers are carried over from the previous model. Good sound quality in medium to large sized rooms, huge bass from 3 downward facing subs. Quite a hungry system so a good strong amp needed to drive it well, I prefer Yamaha, but good results from others as well. These tended to overheat the amps so not to many around.