AudioKinesis Swarm 4 sub array: https://www.audiokinesis.com/the-swarm-subwoofer-system-1.html
Below is an REW spl graph (1:12 smoothing) showing useful output to 20Hz in a 28 x 18 x 8 ft room with the Swarm.
While many subs can get you to 20Hz, multiple subs of any make will get you there with a flatter frequency response and fewer room modes. More data available on my virtual system page.
-and-off-(green)-20-200-Hz.jpg)

