The lastest incarnation of the now iconic Definition was launched this month at the Rocky Mountain Audio Fest in Denver. First launched four years ago, the Definition has undergone quite a few updates in the past few years. The Mk IV is (in Zu’s own words) the greatest speaker they have ever made. The speakers feature he new widebanders (from Dominance) and Event wiring harness, we get a new Radian 850 based tweeter and a completely redesigned cabinet. But that’s not the big news. The big news is the subwoofers. Gone are the rear-firing subs and in is a new down-firing 12″ sub driven by a Hypex UcD 400 amplifier, with a host of user-friendly adjustments. Bottom-end bandwidth has increased to 10Hz-20kHz, but it still carries a 101dB efficiency at a nominal 8ohm impedance.