The Silver Flute line offers exceptional value, build quality, and versatility. The woofer cones and dust caps are made from a special mixture of wool and paper fibers. These wool fibers help reduce cone resonance, and give the woofers a slightly warmer sound than traditional paper cones. The woofers have durable rubber surrounds and robust cast metal frames. The large voice coils are vented through the back plate. All Silver Flute woofers are available in both 4 and 8 ohm. Consider this product for home stereo, surround sound, autosound systems, and commercial line arrays. Please look at the mechanical specifications carefully as terms like 5" and 6.5" are generalizations. Frame diameter 167mm Cut out diameter 147mm Bolt hole circle 160mm, 4.2mm screw holes 5mm flange thickness 75mm depth from back of flange 0.15 cubic foot sealed box for an f3 of 125Hz 0.25 cubic foot with 1.5" diameter vent by 5" long for an f3 of 70Hz 0.4 cubic foot with 2" diameter vent by 6" long for an f3 of 55Hz