Earthquake Sound TREMOR-X154 Tremor-X Series Single 4 Ohm 3000 Watt 15" Car Audio Stereo Subwoofer (pair) Free Air Resonance (Fo): 26,0625Hz Electrical "Q" (Qes): 0.677 Mechanincal "Q" (Qms): 6.9614 Total Speaker "Q" (Qts): 0.617 One Way Linear Excursion: 1.2" (30.48mm)