Control 312CS is an excellent addition to JBL Control 321, 322 and 328 loudspeaker systems, or any full-range loudspeakers, for applications requiring extended bass and additional subwoofer output. The Control 312CS is easy to install. The innovative EZRail™ feature built into the metal baffle temporarily holds one side of the speaker baffle in place until the installer can affix the baffle to the backcan with screws. Control 312CS in intended for systems utilizing an external active subwoofer crossover and separate amplifier channel for the subwoofer loudspeaker(s).