I think the key to good bass, beyond effectively controlling resonance problems below the rooms Schroeder frequency, is ensuring that the woofer accurately tracks and reproduces the incoming bass signal.
A woofers intrinsic setting time or its rise and fall time only has to be the same or slightly faster than the incoming electrical waveform. It can't be as fast as drivers with lower moving mass and fortunately it doesn't have to be.
Unfortunately, I suspect that most of the time the woofers unassisted setting time may be slower than that of the electrical signal driving it, leading to a less than realistic reproduction bass instruments. This where servo control of the woofers signal tracking behavior, in particular, the ability to force the woofer to closely follow the bass waveforms decay characteristics through error correction, comes into its own. There really is no substitute for active control of the woofer, especially if listening to music with synthesizer bass content, which can exhibit bass waveform characteristics that are not subject to the physics that govern real world instruments, such as moving mass.
Obviously the dynamic driver based dipole subwoofer cannot function properly without the presence of servo control of the woofer.
I think quite satisfactory results could also be obtained from a boxed based subwoofer system in a room, albeit, at a greater cost when compared to a H-box based design.
Scotty
I agree if I understand you correctly Scotty. The problem is to keep the total Q about 0,7 or below, such that energy applied are absorbed via various means. This would include optimal losses due to electrical, mechanical of the driver, and the enclosure, whether open or closed.
Above ~0,7, then I agree some sort of feedback/servo control would be beneficial. The higher the total Q, the more energy
not absorbed by suspension, box/materials, then the problem of "settling" time comes into play. Feedback would simulate a lower Q, thus beneficial.
The cost may not be higher at all, if the total Q of the entire speaker is optimized to absorb any excess energy, regardless of type, open, closed etc. That is why I suggest variable controls, at least one to adjust the total Q of the entire speaker. I do on mine, as Danny does, to optimize lower frequency accuracy.
All this helps in the seamless integration of woofer to mid and higher drivers.
cheers
steve