Power up your in-car sound with the XM-S400D 4-channel amplifier. With a continuous power output of 45 watts per channel, your music comes to life with depth and detail. Its compact size allows you to get the sound you deserve without losing any of the space that you need. Some features include: Continuous power output of 45 W per channel (at 4 Ω)1. Enjoy powerful audio throughout the entire car, thanks to the 180 Watts total continuous system power (45 W X 4 RMS). Class-D Technology. The Class-D Technology is a method to convert and amplify music signals with MOSFETs to high speed pulse signals. Furthermore, it features high efficiency and low heat generation. Compact Design. Small enough to fit almost anywhere. Dimensions are 6.5in L x 1.5in H x 2.5in W.