18-inch subwoofer, low frequency complementary system, unit selects materials made by rich experienced technician can endure high temperature. The body of the box adopt straight shoot structure with richer and more natural low frequency, which is strongly recommended to be used as a low frequency complementary in the great sound expanding system. 4ohms impedance and 100dB sensitivity. 20Hz to 500Hz frequency response. 18mm high density board enclosure with black and gray paint surface.