SMAKN&reg; USB Powered 2.1-channel Subwoofer +3D Surround DC 2.5-5.5V Power Digital Amplifier Board Mini Audio Amplifier Excellent full-bandwidth EMI suppression. Excellent on power-off point noise suppression. Up to 90% efficiency,high SPRR:-80gb(217hz). 3D surround sound and integrated 2.1-channel band pass filter function. Over current protection, over temperature protection , under voltage protection.