from the alpine website- Features Designed and Engineered in the USA Hidden Screw Gasket Gold Plated Insert Terminal Block with VC Connection Jumpers One-Sided Terminal Layout Massive Triple Stacked Strontium Magnets FEA Optimized High Excursion Injected Santoprene® Multi-Roll Surround FEA Optimized Mirrored Progressive Nomex® Spiders with Integrated Tinsel Leads FEA Optimized CRC T-Drive Motor Structure with Copper Shorting Sleeve & Heat Transfer Technology Multi-Stage Ventilation System (Dual Flare Pole, Spider Plateau & Frame Leg Venting, Cone/VC Junction Venting) Integrated Spider Landing and Heat Transfer Plate Dual Voice Coil Design, 4-Layer 220°C High Temp Wire with Inner/Outer Winding on Twin-Wall Brass Former Custom Cast Aluminum Frame Carbon Fiber/Aluminum Honeycomb Parabolic Cone Power Specifications 3000 Watt Peak Power 1000 Watt RMS Power Impedance: 4+4 Ohm Sensitivity 86dB/W (1m) Frequency response: 20-500Hz Mounting depth: 221 mm Cut-out diameter: 277 mm