The HDS200 series is a revised version of our SDC2.5. The major differences you will see is the switch from a cast basket to stamped, and the addition of push connectors instead of the direct leads. These woofers also have an added cooling option to the backplate, which the SDC2.5 was lacking. With these changes we were able to drop the prices for you all. The HDS200 series is a great woofer for those not looking to upgrade their charging system but still want to rattle their car. At 600W RMS with a 2.5" coil they are capable of fitting in smaller enclosures for placement with stock installs and everyday street beat. We do suggest putting these, along with all of our woofers in ported enclosures due to the suspension set-up. (Two pairs of spiders, one wired, one non.) * Model: HDS210 * Piston Diameter = 203.2 mm * f(s)= 37.01 Hz * R(e)= 7.32 Ohms * Z(max)= 75.67 Ohms * Q(ms)= 5.817 * Q(es)= 0.623 * Q(ts)= 0.562 * V(as)= 12.050 liters (0.426 cubic feet) * L(e)= 6.79 mH * n(0)= 0.09 % * SPL= 81.81 1W/1m * M(ms)= 226.60 grams * C(ms)= 0.08 mm/N * BL= 24.88 * Model: HDS212 * Piston Diameter = 254.0 mm * f(s)= 39.03 Hz * R(e)= 7.43 Ohms * Z(max)= 75.33 Ohms * Q(ms)= 5.367 * Q(es)= 0.587 * Q(ts)= 0.529 * V(as)= 29.700 liters (1.049 cubic feet) * L(e)= 7.74 mH * n(0)= 0.29 % * SPL= 86.68 1W/1m * M(ms)= 201.90 grams * C(ms)= 0.08 mm/N * BL= 25.03 * Model: HDS215 * Piston Diameter = 330.2 mm * f(s)= 36.34 Hz * R(e)= 7.47 Ohms * Z(max)= 69.87 Ohms * Q(ms)= 7.483 * Q(es)= 0.895 * Q(ts)= 0.800 * V(as)= 73.310 liters (2.589 cubic feet) * L(e)= 8.41 mH * n(0)= 0.37 % * SPL= 87.84 1W/1m * M(ms)= 269.40 grams * C(ms)= 0.07 mm/N * BL= 22.65