MS101-4 Powered Monitor Speaker With the controls (power switch, volume and tone controls) and the combo jack input on the lower front panel, the MS101-4 is simple and easy to operate. The sturdy metal grill offers complete protection for the four-inch cone driver, while the rear panel is equipped with one stereo mini and two TRS Phone input connectors, and an AC inlet for excellent portability. The bass reflex port is also located on the rear surface, resulting in a more compact chassis. The MS101-4 offers a compact, lightweight form that is both portable and durable.