Magnepan 20.7 and Subs

Wharfdale did the sand. Bozak's claim to fame was infinite baffle speakers. There are lots of sub kits out there now and if you have some woodworking experience and some basic tools by all means. Dayton makes a very advanced plate amp with room control.

It is extremely difficult to control resonance in box speakers. The kit manufacturers because of weight limitations and cost to not dig very far into the problem. If you are capable,  making your own enclosure is the way to go. Calculating volume is easy once you know your driver's parameters. It is just plug in math. Tricks to control resonance are first use very thick walls. In MDF 2 inches minimum. Keep the sides, top and bottom as narrow as possible but make the top and bottom wider than the sides are tall so that they resonate a different frequencies. You want to make things so stiff that the cabinet resonates at a frequency as far above the woofers cut off point as possible. The heavier the better. You do not want the whole cabinet shaking. Always three spiked feet and right into the floor. No pads. Ideally with the woofer pumping out it's lowest frequency you should feel nothing with your hand on the enclosure. Any movement or vibration that you feel is distortion. You will never feel a commercially made sub that quiet with maybe the exception of the big Magico subs. Get a piece of granite cut to size and silicone it to the top of your enclosure. The added weight always helps and you can get granite cut offs for cheap. I prefer external amps and cross overs. JL Audio makes a nice external crossover.  

As the OP, I have to say first of all that I listen to pretty much only classical music. OK, a bit of jazz here and there. I find the bass on the 20.7’s not only adequate but PERFECT really. I think my original idea to supplement them with subs comes from the fact that I CAN (financially anyway), and also from the fact of my never ending need to "improve" things. So I’ve pretty much decided not to invest in a pair of subs because I'm rather convinced that I would simply be creating more "problems" to solve.  There are folks in this thread who really know more about what they’re talking than other folks but its up to you dear reader to DISCERN that. Just remember, more experience = better advice. @jafant The only other development is that ODDLY, I have gone back to the Aesthetix Atlas as my amp of choice with the Maggies at the moment. I’ve gone back and forth between the Atlas and the Pass X150.8 (also thinking that perhaps I should move up in the pass line to a more powerful amp). But the Pass product is SIGNIFICANTLY warmer in the midbass. The Atlas is incredibly airy, perhaps a very slight TINY smidgen "clinical" but still very very good. I did think about attenuating the midrange panel using a resistor on the 20.7s with the Pass to see what that would do and I may still experiment with that. There’s absolutely no doubt that the Pass did WONDERFUL things for my Thiel 2.4s but I don’t like it anywhere near as much with the Magnepan 20.7s, MUCH preferring the Aesthetix Atlas as my amp at the moment.

@pwhinson, if cost is no object, and your 20.7’s give you enough output in the bottom octave (20-40Hz), look into the Eminent Technology TRW-17 Rotary Woofer. IAR’s Peter Moncrieff has characterized the TRW-17 as the world’s only true "subwoofer", as it is designed to reproduce only 20Hz DOWN! It provides substantial output all the way down to 1Hz, possible because it is not a woofer (whether cone, planar, horn, or any other traditional driver) pushing air, but a rotary fan. It’s a fascinating design (and it’s creator Bruce Thigpen a very clever and creative fellow), so head over to the ET website to read all about it.

I'm a newbie Maggie 20.7 owner as I just received a pre-owned pair in excellent condition. The SQ and feeling that the artists are in the room with you is unbelievable.  I would like to trial the use of a sub to allow the sub to handle frequencies at about 50Hz and below.  With all the positive remarks about Rel subs, is there a way to connect the Rel so that it limits the frequencies to the Maggies to 50Hz and above or is a crossover needed for this? 

I apologize if this is a common question answered in several places.