XDi 450.4 - Arc Audio 4-Channel 450W XDi V2 Amplifier XDi 450.4 - Arc Audio 4-Channel 450W XDi V2 Amplifier 4 Channls at 4 ohms: 85 Watts | 4 Channels at 2 ohms: 125 Watts | 2 Channels at 4 ohms: 250 Watts Selectable Impedance optimization allows full power output at either 2 or 4-ohm stereo operation. (On Selected Models) Flexible mounting orientation for vertical or horizontal installations. Dimensions: 8.173"(L) x 6.268(W) x 2.086"(H)