Cone Area (Sd) : 467.59 sq. cm D.C.Coil Resistance (Re) : 3.6 ohm Electrical Q (Qes) : 0.47 Equivalent Suspension Stiffness (Vas) : 150.31liters(xxxxcu.ft.) Free Air Resonance (Fs) : 19.64Hz Frequency Response : 26Hz - 1kHz Impedance (Nominal) : 4 ohm Mechanical Q (Qms) : 10.71 Total Loudspeaker Q (Qts) : 0.45 These are some of the specs of the Alpine 15" Type R sub for car audio. I can get these at a really good price. The only thing it doesnt list is Xmax and I'm sure I could call the company and find out. Then here is another sub, the MTX Thunder 8000 15" also a car sub. Fs 24.6hz Vas 145.5 L Qts .37 Qes .40 Qms 5.69 Xmax 12.5mm D 13.267 Spl 89.3 Im deciding between these two and the Tempest driver for a ported or sealed cube to go under my svs 20-39. Ideas??