Others experience re: subs and Magmepan 20

imdoc,

     I'm also a Magnepan user but not with quite as good of a model as you own. I've had a pair of older 2.7qrs for about the last 25 yrs  that are rated to go down to 37 hz while your 20Rs are rated as going as low as 25 hz.
     I've been searching for a good bass system to pair with my Magnepans for over 2 decades. The only sub system I've discovered that has very good bass response down to the lowest audible octaves that is more impactful but just as natural, textured, detailed and articulate as the bass my Magnepans produce down to their limits and blends in seamlessly is a Distributed Bass Array System (DBAS).  

    There are actually 2 DBAS that I'm aware of:

1. The Audio Kinesis SWARM which I believe is the original.  It's based on the PHD thesis of an acoustical engineer, Dr.Geddes, on the subject of achieving good and well dispersed bass performance in smaller rooms (as opposed to large venues such as concert halls and auditoriums) and the work of another acoustical engineer, Dr. O'Toole.

2.  The Audio Kinesis DEBRA(Distributed EQ Reflex Array) which is basically the same as the SWARM with minor variations in sub construction that is built and sold by James Romeyn Music and Audio in Utah.  James is a friend and partner of Audio Kinesis owner, Duke LeJeune, and has a licensing agreement with Audio Kinesis to build and sell his version under the Audio Kinesis brand.

     About a year ago I purchased the Audio Kinesis DEBRA  system.Here's a link describing the system:

http://jamesromeyn.com/old-pages/home-audio-gear/dsa-1-0-distributed-subwoofer-array-5-pieces-4k-usd...

Since it is such an ideal system for me and I think it would work well in your system, I provided a link to  the Absolute Sound's 2015 review of the Audio Kinesis SWARM (which awarded it a 'Golden Ear' award for that year) below:

http://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/

.

    I can personally attest to the effectiveness of the DEBRA system in my room. I have 6 listening/viewing positions in my combination music and ht system in my living room. Bass response is equally good for music and HT at all 6 positions without the use of acoustic devices (no absorbing or diffusing panels or bass traps) and without any electronic equalization (room analysis/correction equipment, software or eq). I should mention I've never had my system/room analyzed using a mike and software.  

    From my purely subjective perspective, however, I'm confident the results would be good since I spent hours on the setup and critical listening from all six listening positions in my room. I would suggest this type of sub system as a viable alternative for anyone considering investing in one or more quality subs. The system is rated clean at 113 decibels at 20 hz and I've often heard and felt it go this low.  It feels and sounds clean and right but I can't verify the decibels or lack of distortion.

Hope this helped,

  Tim

a Moog might go a lot lower than 20 Hz on rock tracks

otherwise, sub 30 Hz sounds are pretty much limited to organ music and cannons (Tch. overture)

I’d bet some DSP testing and room treatments would be much more rewarding, tho maybe an amp that really put out a lot of current into 4 ohms(?? dunno what you have now)

Wendell can give you the factory talk on why to avoid cone based subs and to use a pair of DWMs instead

OTOH, many people are happy with (at least the expensive) subs added to the smaller panels

imdoc,

    Forgot to answer one of your questions:
Whether I thought the $3,000 cost of the  DEBRA was worth the cost?

     Unequivocally, yes.  I honestly can't count the number of times I've been listening to music and the music calls for deeper bass (acoustic, percussion or electronic) and the DBA system just powerfully, naturally and seemingly effortlessly reproduces the lowest octaves and blends so seamlessly with the Magnepans reproducing everything else that the result is a sound stage illusion that  just sounds like a beautifully synchronized realistic whole; like the actual musicians are playing in my living room or as if I've been transported to the venue, depending on the recording.
  Logically I know it's a sound stage illusion but it's uncanny how I perceive the bass, even though it is monaural, as emanating from the proper instruments within this illusionary and 3D sound stage.  It's really quite impressive and enjoyable.  .
   I think paying attention to details and being precise in setting up a DBA is critical to getting good results; things like following the progressive locating procedure for properly positioning each of the 4 subs in the room, using trial and error to set the crossover at the correct hz (I found 40hz worked best in my system),  determining the correct relative volume of the DBAS (in relation to your main speakers) by precise setting of the supplied sub amp's rotary volume control knob (mine is set between the 9 and 10 o'clock position) and whether to run your main speakers full range or use a filter to limit their lower frequency duties (Mine run full range without restriction).

    Fortunately, this rather elaborate setup process only needs to be done well once.  You're able to just enjoy your music with consistently stellar performance until you decide to move or upgrade your main speakers. 

     Lastly, I wanted to mention that you can also construct your own custom DBA by using 4 subs of your own choosing.  However, this is likely to be significantly more expensive than a DEBRA or SWARM complete system with the 'law of diminishing returns' also needing to be considered.

Thanks,
 Tim   

I currently have Magnepan 20.7's paired with a single REL G-1 sub-bass driven by ARC 250SE mono-amps. I have found the sub provides an additional fullness and body to music which has been linearly recorded and accurately transcribed to less than 30hz (CD or LP). The improvement in overall presentation is also dependent upon the room size, and in my case, I listen in a 15ft wide by 22ft long room. I would note that I previously had Magnepan 20.0s, and the improvement with a sub was somewhat greater due to its more limited low end.  Due to the inefficiency of Magnepans, ample dynamic power is essential and probably more important than the addition of a sub.     

I have a pair of Magnepan MGIIIa s and now that I have a preamp with dedicated subwoofer ouputs with adjustable crossover points, I was thinking of adding an REL or a Magnepan DWM to the system.  I am thinking more like an 8" sub, since I want a faster response than I think the larger subs will provide (do not really need super powerful bass) and my listening room is not large.