Subwoofer - Interface help?

Hello, I want to buy a powered active subwoofer but I'm not sure how to set it up. I have a Steinberg UR22 interface but both the outputs are being used by my Alesis monitors. On the back of my right monitor though is a port for a 1/8" stereo/sub output cable. Would I need to buy an adapter for the subwoofer to connect to the monitor?

It depends on the setup... With a home theater setup the receiver handles the crossover & bass management. The active/powered subwoofer may have a low-pass filter, or it may not. Sometimes the subwoofer has an active crossover where the full-range left & right signals go into the sub. The left & right bass are mixed and sent to the subwoofer. The left & right signals come-out of the sub with the bass filtered-out and these signals are sent to the left & right monitors. has a crossover built-in. Sometimes the full-range signal is sent to the sub where everything but the bass is filtered-out. The full-range signal is simply sent in parallel to the left & right speakers (with Y-Adapters). That means the bass is also sent to the left & right speakers.

unless your audio interface has a subwoofer out, i guess you'll have to designate an output for the sub and designate a cutoff frequency for it and the other monitors manually with plugins. the monitors will be above and the sub below. a monitoring system intended for this would do the cutoff stuff for you i should think.