While I am a huge advocate of acoustics treatment, the op mentions they have a small listening space (Hey op, what are the measurements). Good, emphasis on good, bass control with acoustic treatments means large acoustic objects. That may not be feasible in the space. With the exception of resonators, which can still be large to be effective, or too narrow band, any absorber is going to be big. With two subs, the nodes will be much less pronounced and easier to control with acoustics.
erik_squires8,841 posts04-17-2020 1:59pmSpend all the money you were going to spend on a 2nd sub and treat your room first. Talk to GIK. Then see if you still feel a 2nd sub is needed.