One thing you might consider in a two-channel context is that a subwoofer that's "flat" anechoic will have a rising response due to room gain. Typical room gain is +3dB per octave from 100 Hz down to about 20 Hz. In my experience, a subwoofer whose anechoic output falls by 3 dB per octave over that range is less likely to sound boomy.
http://www.speakerbuilding.com/content/1020/rge.gif
Also, there's a correlation between in-room bass smoothness and the number of low frequency sources spead around the room. A dipole can be thought of as two monopoles, one with reversed polarity. So two dipoles would be expected to have in-room bass smoothness comparable to that of four monopoles. People who have compared one sub vs two subs pretty much invariably prefer two subs because it sounds more natural. Imho to blend well with dipoles, four subs are called for. I spent years experimenting with different types of subwoofers (sealed, isobarik, transmission line, dipole, aperiodic, etc) to find what would match the "speed" of a dipole. Then in a conversation, a physicist friend of mine described to me the advantages of multiple low frequency sources, and so I tried that and it worked better than all the esoteric designs I'd been trying. So if the goal is quality rather than quantity, my suggestion would be multiple smaller subs rather than a single ubersub.
Duke
dealer/manufacturer
http://www.speakerbuilding.com/content/1020/rge.gif
Also, there's a correlation between in-room bass smoothness and the number of low frequency sources spead around the room. A dipole can be thought of as two monopoles, one with reversed polarity. So two dipoles would be expected to have in-room bass smoothness comparable to that of four monopoles. People who have compared one sub vs two subs pretty much invariably prefer two subs because it sounds more natural. Imho to blend well with dipoles, four subs are called for. I spent years experimenting with different types of subwoofers (sealed, isobarik, transmission line, dipole, aperiodic, etc) to find what would match the "speed" of a dipole. Then in a conversation, a physicist friend of mine described to me the advantages of multiple low frequency sources, and so I tried that and it worked better than all the esoteric designs I'd been trying. So if the goal is quality rather than quantity, my suggestion would be multiple smaller subs rather than a single ubersub.
Duke
dealer/manufacturer