The 3000 Series subwoofers feature SFB cones, which have unprecedented rigidity and low moving mass, driven by a high precision 240 oz magnet motor, machined, to give you that particular DD sound in a closed case. The 3000 series includes the Evolution subwoofer package (ESP) sporting a deeper frame than standard sub and an exclusive design with surround and cone. ESP divers are built to maximize performance in the recommended size class.