Next check out the Discus subwoofer’s front side to see the injection molded polypropylene cones and inverted dustcaps. Through the I.M. process, MB Quart engineers have precisely tuned these driver components for super low frequency response. A subwoofer cone with uncontrolled long excursion will not create desirable ultra low-frequency response with impact. MB Quart Discus subwoofers incorporate a steep ¾” UV stabilized NBR rubber surround that permits the Discus subwoofer cone to behave like an extremely stiff piston. It’s not uncommon to find another brands subwoofers touting cone excursions approaching 1-inch. Most of these other designs suffer from uncontrolled cone wobble. Encircling these NBR surrounds you will find absolutely “Nothing”, as in no visible mounting screws. This feature is due to a removable and paintable trim-ring that neatly conceals the Discus subwoofer’s mounting screws.