Both Sonos subwoofers have a frequency response as low as 25Hz. The difference is going to be in the volume each subwoofer can output. The Sub Mini is intended for small- to medium-sized rooms.

You can learn more about duel subwoofer compatibility on the Sonos website. Given its premium performance, the Sub 4 works best with an Arc Ultra, though you can still use it with the smaller Beam ...