Polypropylene Woofer Cone We have molded a proprietary cone to ensure that there is minimal cone flex at the woofers excursion limits which keeps distortion low and output tight and deep. Progressive Spiders JBL uses progressive spiders the Series II subwoofers to provide the best possible control at the excursion limits versus much more commonly used linear spiders. The benefit is a far more controlled woofer stroke with far tighter bass characteristics. Stitched-In Tinsel Leads We have stitched the tinsel leads right into spider to ensure long woofer life and minimize the chance of lead breakage. This feature is all about JBL building products that last. Vented Frames We have vented the frame on the Series II subwoofers to keep the motor cool which gives you more power handling and a woofer that last. JBL Life Testing Is Serious Business To ensure that our speakers stand the test of time, we utilize the same rigorous quality control and testing standards we employ on the products we manufacture for professional and OEM applications. This includes vibration testing that generates almost 1.9G’s with a varying frequency from 5Hz – 1kHz, Lifecycle testing which pushes each product to its limits with 500 hours in an environmental testing chamber. Here we freeze, bake and give every product a sunburn with 150 hours of ultraviolet light. We also drive each subwoofer for 100 hours at rated RMS/Peak power using specific frequencies and music. Our competitors simply do not have the tools or expertise to do this.