What are the best subwoofers to use with Magnepan 20.1s?

James Kates published a paper in the Journal of the Audio Engineering Society years ago that showed dipoles to have smoother in-room bass than monopoles.   Since getting smooth in-room bass at low frequencies is difficult at best, getting in-room bass from a subwoofer system that can subjectively keep up with dipole mains is even more of a challenge. 

Note that smooth bass = fast bass, because the in-room peaks correspond with longer decay times.  The good news is that when we have smoothed the frequency response we have fixed the time domain response because they are the same problem.

Dipole subwoofers seem like the obvious solution, but dipoles have a subjective lack of impact down low.  They don't give you that chest-compression WHACK! that a good monopole sub does.

One way to have both smooth bass and impact at the same time is to use a distributed multi-sub system.  Four subwoofers intelligently distributed around the room will be inherently far smoother than a single unequalized sub, and that smoothness will hold up pretty much throughout the room, which is not the case with a single or even a pair of equalized subs.  Remember smooth bass = fast bass.  And those four subs can be fairly small because, well, there's four of them. 

The Absolute Sound awarded a 2015 Product of the Year award to a four-piece multisub subwoofer system, so apparently the concept works well.   You can of course cook up your own version with Rhythmics or Vandersteens or RELs or JLs or whatever.  

Duke

dealer/manufacturer/multisub advocate

Two points:

- The Rythmik sub plate amp allows for high-level hook-up to binding posts (on the main speaker’s power amp), like Rel’s.

- OB/Dipole subs (such as the GR Research/Rythmik), their figure-of-8 radiation pattern creating a null to each side of the sub, do not excite the sidewall-to-sidewall resonance mode that Monopoles do, therefore creating less of the "room boom" often associated with and attributed to subs.

There is, unfortunately, a price to be paid for those otherwise-advantageous nulls: a corresponding bass cancellation that increases with descending frequency---a 6dB/octave, 1st order acoustic roll-off. Rythmik designer Brian Ding compensates for that roll-off by installing a complimentary 6dB/octave bass boosting "shelf" into the plate amp which comes with the OB/Dipole Sub kit, which counter-acts the roll-off, resulting in bass response claimed to be flat into the teens. Clever fellow.

When using a Magneplanar Tympani as bass augmentation, the panel can be butted right up against a side wall, with a significant resultant benefit: A prevention of the normal dipole cancellation, as the front and back opposite-polarity waves can’t meet and cancel each other, the path obstructed by the wall. That results in the absence of the 1st order, 6dB/octave roll-off inherent in a dipole speaker. Hence, no dipole bass roll-off (at least not from that end of the panel). Free extra output to a lower frequency, with no extra cost, or penalty!