HIFONICS ZST-8D2 ZEUS Flat Woofer Subwoofer. 20 cm flat subwoofer 500 watts. Power 250 W RMS / 500 W max. Impedance 2 + 2? 50mm / 2.0 VC. 40 oz double magnet. Fs 40.7 Hz. VAS 10.1 L. Xmax +/- 15 mm. Installation depth 78 mm. Installation opening 182 mm. Zeus ZST series / flat subwoofer. In the sizes 8 “and 10″ for small housings. Please Note: These are Dual 2-ohm subwoofers we also Dual 4-ohm subs in stock.