Magnepan 20.7 and Subs


I've been reading about supplementing my Magnepan 20.7s with a sub, the general preference being REL.  However in room I'm getting fairly deep bass with the 20.7's, so my sense is that I would put the crossover on the REL pretty low, probably at 30Hz, leaving only sub 30Hz material porting "also" to the sub to augment the natural deep bass of the Magnepans.  I'm just wondering since there's precious little info in the 15hz to 25hz range, do I really need a PAIR of RELs, or could I get by with just one?  And shouldn't that one be capable of going REALLY low, like the G1, or what's the point?  Any advice would be appreciated.  Thanks.
pwhinson
The obvious answer is start with one and if that does the trick you’re done. If it doesn’t, then get a second. Many years ago I had a pair of MG2.6’s and one subwoofer worked wonderfully 
Most subs are themselves already rolling off at 30Hz. If you have the $, look into the Eminent Technology TRW-17 Rotary Woofer. It’s intended use is for the bottom octave (20Hz-40Hz) and below.
Stereo pair always sounds better.... but one in center works OK too.
Get one ... try.... either like it or buy another.... easy button.
Now go get a second job to pay for it... :)
My experience with 20.1’s may be of some value. Tried a pair of REL’s about 10 years ago, ended up working on the room acoustics to improve bass response. Now raggae music for example (Steel Pulse) kicks me in the gut (like it’s supposed to ;-)). Maggie’s strengths are a result of freedom from speaker enclosures, subs didn’t compliment them at all for me. I found dealing with the back wave using traps and diffusers made the bass very clean and deep. Good luck!

Duane
It's been over a month since I got my 20.7 as a new unit. It had too much bass and treble in the beginning, and I had to use attenuator for treble and adjust the bass with equalizer. It took over a month finally to stabilize the balance, I removed the attenuator and no tone adjustment.  

Magnepan never mentioned about breaking-in period but surely it needs to do so. I thought it was defect in the beginning. But I had to get more powerful amp and it helped for tonal balance.
I love 20.7s. Great speaker. They do bass better than most dipoles but still suffer a bit below 40 Hz. The cross overs are at about 450 and 3500 Hz and they are usually pretty slow. 12 db/oct. Putting subwoofers in will clean them up a bit and increase impact. You will need at least two subs and ideally 4. I would cross at 24 db/oct  100 Hz. I think the JL Audio f112s would be wonderful as a pair. But if you want the ultimate in powerful performances 4 all right up against the front wall with two in the corner and the other two equally spaced along the front wall. With the 20.7 driven by proper 200 watt or better mono amps you will be rocking for sure. 
Post removed 
Elizabeth, that bassiness you describe can be adjusted by moving the speakers away from the wall which in an attached condo might be a problem due to room. The bass that is annoying you is between 150 and 50 Hz. If you have a test record with frequency tracks you can hear exactly where the problem is. Now interestingly enough if you get two subwoofers and cross them just a little higher 125-150 Hz you will have more control of your bass just by turning the subwoofer volume down and get the advantage of further cleaning up an already clean loudspeaker. The longer bass excursions doppler distort the higher frequencies, it modulates them. It is one of the most important reasons for using subwoofers with planar dipoles.

Mike
pwhinson
any new developments on this thread? Hope you are well and enjoying Summer.  Give us an update as your Maggies continue to bloom and settle into your room/system.
Happy Listening!
The 20.7 will go down to 25Hz in a good room with proper setup and a decent power amp.

There is a noticeable sonic transition to subs with tall Magnepan’s, because Magnepan’s have tall bass waves, and subs have short bass waves.

Some do not like planar bass, with it’s natural sound for acoustic instruments, they like punchy, dry bass, that box speakers put out with with rock ((since rock bass is played mostly through boxes.

I have Magnepan IIIas and 3.6s and guests always ask me where the sub woofers are?
There are none! I know how to setup Magnepan’s in an appropriate room.
don_c55, Magnepans are linear radiators down to about 150 Hz. Below that they are point source radiators just like any single sub woofer. Maggies will make bass but it is very lumpy for lack of a better term. Not only is their response not smooth but input below 50 Hz really shakes the speaker distorting everything else. I prefer 4 subs with 20 series Maggies using 12 inch drivers and crossing up at 125 Hz essentially keeping the system Line Source throughout. You also have to high pass the 20.7s to get the full benefit so you really need digital bass management to do it right along with room control. Now we are talking serious money. It is best to avoid subs unless you can do at least two. Single subs will just get lost and cause a lot of heart burn and frustration.
Setting up Maggies to get the smoothest bass is just a matter of adjusting the distance to the wall until you get what you want but it will never be the smoothest base because you can not avoid dipole interference and cancelation effects off the front wall. Wasting money on all kind of room treatments will not change or correct this. 

Don, I share your amusement at you being lectured to on the subject of Magneplanars. Those who know Don are aware of the fact that he has forgotten more about that loudspeaker (having owned them since the 1970's) than most will ever know. Don also has a ee education, and it is HE who should be giving the lecture.

Don could talk about the fact that below 150Hz the Magneplanar bass panels (separate in my Tympani T-IVa) continue acting as dipole radiators, with a null to either side, therefore exciting one less room dimension mode. There is one hi-fi enthusiast (I need to find his name) who uses Martin Logan ESL's as his mains, Tympani bass panels as woofers (it reproduces the sound of my self-recorded Gretsch 26" bass drum more like it does in life than any other reproducer I've heard), and an Eminent Technology TRW-17 Thigpen Rotary Woofer as a "true" subwoofer (20Hz-down!). Now THAT is a system I would love to hear.

There is no need for "digital bass management" to high pass the 20.7; a First Watt B4---all discrete, no opamps, no ic's---works perfectly. So will a Pass or Marchand x/o. If a 1st-order filter is steep enough for your needs, you can even install a simple capacitor/resistor filter on the input jacks of the amp powering the 20.7's.

This is all old news to Maggie enthusiasts, and much more info about the speakers is available on numerous forums, including the Planar Speaker Asylum.

bdp24, I have owned my fair share of Maggies and have installed more than all of you have ever listened too. Yes they are dipoles and do not radiate to the sides but that has absolutely nothing to do with what happens at the front wall and how that affects the speakers bass response. I am not here to give you a lesson in acoustics if you want to learn more about dipole interaction with a wall there is loads written about it. You will never get completely smooth bass response out of any dipole unless you have it out in open air or live in an alternative universe. 
Having said all this there are very few loudspeakers I would choose over a 20.7. I just wish they had decided to do an 8 foot version. That would have been the nuts.

Oh yeah? Well I own Tympani T-IVa’s ;-) . And have heard the 30.7, though in a bad sounding demo in a really poor room. Wendell Diller was not pleased. But to get back to the point of yours that I am contesting, it is your statement that below 150Hz Maggies are point source radiators. That is simply not true; they are absolutely dipoles at all frequencies, including below 150Hz. Q: What magically transforms Maggies into behaving as point source radiators at 150Hz and below? A: Nothing. Your post directly above seems to find you subtly backing off your earlier statement to that effect.

The matter of their interaction with the wall behind them is a completely different subject. By the way, @don_c55 uses four Rythmik F12 subs with his Magneplanar MGIII’s, and has chosen to employ absorption on the wall behind the panels, rather than diffusion.

@bdp24

I do not use any subs with my MG IIIa speakers.

The MG IIIas are in my home theater and MG 3.6s are in my main room.

They are both flat to 30Hz and I do not feel the need for lower bass.

I am more than satisfied.

Bass below 30 Hz has little musical info. Low bass peaks and dips are hard to deal with in my rooms.

I also like to keep peace with my neighbors below in my condo.

I rarely playback much over 90 dB except when neighbors are gone.
OMG @don_c55, I've been conflating you with a regular on the Rythmik Forum. So sorry!
@bdp24

You are right that I am an EE and have owned and listened to 6 foot Magnepan’s every day since the 70’s.

I do show up on several forums under different screen names.

But never use subs or even modified Magnepan’s.

I like them natural and not abused!

I replace the fuses with brass tubes and steel jumpers with 12 gauge ofc wire although.

I also use Cardas golden cross “classic” speaker cables.
My two cents about subs and Maggies.  I have had 5 pairs of maggies, currently 3.5s with Mye stands which were rebuilt by Magnepan last year.  I have always used my Maggies with various velodynes and now Rythmik.  I have run them full range with the subs rolling off in the high 30hz range, and crossed over.  

In my experience, Maggies work best high passed with the subwoofer picking up the bottom two octaves (20-80hz).  They are more open and it helps eliminate the large bass resonance that Maggies have in the 40-50hz range, depending on the model.  The key I found was a good a crossover, otherwise the Maggies just sound veiled.  In my case, an NHT active crossover (X2), that is fully balanced provided the necessary transparency to work well.  The First Watt crossover is supposed be excellent, but is single ended only and about $1500.   
I should add, that while Maggies can output into the 30hz range, their output capability is limited.  I have slapped the panels on every pair of maggies I have had when turned up and trying to reproduce lower frequency information.  A crossover and outboard subs eliminates this issue.  That said, I primary listen to modern music which often has high levels of bass, whether synthesized or due to the mix.  

Excellent posts @mcreyn. The Rythmik subs are finding favour with a fair number of serious Maggie (and ESL) owners. The standard sealed models (F12, F15) are the norm, but the OB/Dipole model (developed in cooperation with Danny Richie of GR Research) is beyond compare. Danny himself uses a pair of the OB’s at the front of his room, with a pair of F12G’s at the rear, mated with his own loudspeaker designs (some employing the great NEO ribbon drivers).

As for Maggie bass, where they really excel is in the midbass, and no other model as well as the Tympani bass panels (two in each speaker), which are separated from the third m/t panel. Except the new 30.7, of course! Good cone woofers for the 20-40Hz bottom octave and Tympani bass panels above that is pretty unbeatable (the OB/Dipole Sub is the only one of my experience that is comparable to the Tympani bass panels.). Only thing left to add is an Eminent Technology TRW-17 Rotary Woofer for 20Hz and below ;-) .

Bdp-24 - When properly powered there is no speaker that does drums as well as a large maggie.  
@mcreyn, right you are. I use the Sheffield Drum Record direct-to-disk LP to evaluate loudspeakers, and that’s why I still have a pair of Tympani T-IVa. Nothing I’ve heard equals that speaker for the percussive attack of a stick on a drumhead, the hard felt beater of a bass drum pedal on a 24" head (I have recordings of my own Gretsch and Ludwig drums), and the hard felt of piano keys hitting the strings. It’s "pretty good" in other ways, too ;-) .
bdp24, I think you are confusing terms. The opposite of dipole is unipole.
Yes, Maggies are dipole throughout the frequency range as they radiate from both sides but 180 degrees out of phase. Bipoles are speakers that radiate from both sides but in phase. My sub design that we spoke about is a bipole. Linear arrays or line sources oppose point source speakers. To radiate as a line source a speaker must be taller than the wavelength it is to reproduce or terminate both ends at a boundary such as the floor and ceiling. My 2+2s are line sources down to 1 Hz because they do just that which is why I wish Magnepan had decided to make the 20.7 almost 8 feet tall. 20.7s are 6" 7" tall that would correspond to a wavelength of somewhere between 150 and 200 Hz. They are too short to abut an 8 foot ceiling thus they become point sources certainly below 150 Hz. Thus their bass power drops off rather dramatically at a distance. On top of this you have the issue with the front wall. If you put the speaker three feet from the wall sound bounces off the wall then rejoins the front wave 6 feet later exactly in phase with one frequency around 150 Hz but 0.6 microseconds late. Every foot equals 0.6 microseconds at sea level. At every other frequency it becomes progressively out of phase but still 0.6 late. So what you have here is smearing of the transient response and alternating amplification and attenuation of the signal resulting in rather monotonous bass. It is easy to dampen signals above 200-250 Hz but it is very hard to stop long wavelengths. Whether anyone likes this or not the best way to deal with this problem is to keep the dipoles as far away from the wall as possible and cross to subwoofers as high up as possible. Since Maggies become point source for sure by 150 Hz two subs in the corners will work fine. 
Now about digital bass management. You not only have to provide the right crossover for your speakers but you also have to make sure the subwoofers are in phase with the satellites. You simply can not do this in the analog world. You have to delay the signal of the satellites long enough so that the signal from the subs has a chance to catch up. The exact amount has to be measured with a microphone by impulse testing which the better room control units like the Trinnov and TACT do automatically. Some subs allow you to adjust the phase angle which is an improvement but it does not correct in the time domain which is ultimate. The Tact will actually allow you to use any seat in the room as the listening position by adjusting the arrival times of all the speakers so that they get to any single listening position at exactly the same time. Very spooky. So, you can have a preset for any position. If your friend wants to sit in the far left seat select the preset for that position and they will have a perfect image. 

Although Elizabeth doesn’t like it when I say this, 3’ away from the wall behind them is insufficient for any planar loudspeaker. 5’ is about the minimum, to create at least a 10ms delay between the front wave and back wave reaching the ear. As Liz accurately said, it is actually not the distance from that wall that matters, but the time differential between front and rear waves reaching the ear. As long as an at least 10ms delay is created (the more the better), it doesn’t matter how that is achieved.

Subs with a phase control allowing continuously-variable adjustment---as do the better Rythmiks (0 to 180 degrees)---make possible time alignment between loudspeakers and subs. I would not buy or own a sub without that capability.

I’ve long understood the opposite of dipole to be monopole, but that may just be semantics. I’ve never heard a bipolar loudspeaker I’ve liked, including the highly-regarded (by others) Mirage. "Line source" and "dipole" are not synonymous.

No they are not and I agree. I have never heard a full range bipole speaker that I have liked. Although I think unipole line sources are a step in the right direction all the ones I have heard have suffered next to dipole ribbons and ESLs. Variable phase in a sub is also a step in the right direction but very difficult to set up by ear and it does not correct the time issue. Assuming the Subs are behind the satellites as is usual. Even though the phasing can be correct the timing can not be. Using digital delay on the satellites works perfectly especially when you have a computer making the adjustment. We use to move the subs back and forth to get them in phase but as soon as you separate them from the wall you lose power, a no win situation. As for keeping dipoles away from the front wall it depends on where you want to amplify the bass. 5 feet will give you a peak at around 100 Hz which will give bass more impact but below that things will roll off quickly. You also interfere with the room more. Again the best solution is to move to a subwoofer array at 125 hz which gives you much flatter bass and allows you to keep the dipoles closer to the wall. I always dampen the wall directly behind the dipole with acoustic foam tiles which kills the primary reflection above 250 Hz tightening up the image. There is no significant radiation in any other direction except straight forward. Perfect!

The time/phase issue between speakers and subs has to take into account the nature of the x/o between the two. 1st, 2nd, 3rd, and 4th order filters all create different phase relationships, both between the drivers within the loudspeaker itself, and between it and any sub. Brian Ding has a detailed discussion of this issue in the technical section on his Rythmik Audio website. His phase control provides delay of the woofer output in milliseconds---which is the same as moving the sub further behind the speaker. He reminds readers that the opposite is not possible: moving the output ahead in time ;-).

But of course, if you delay the sub enough (16ms on the phase control), it will be in opposite polarity (180 degrees)---equivalent to moving the sub in front of the speakers. Danny Richie of GR Research also sells the Rythmik Subs, and his "baby" is the OB/Dipole model, as well as the "G" version of the Rythmik F12G (the G is from GR Research, and that sub has a paper cone woofer. The standard F12 has Brian Ding's aluminum cone woofer).

Danny is a crossover design expert and OB speaker enthusiast/specialist, and is happy to provide advice on phasing (and any other matter) between the subs and any speaker you may be interested in pairing with the OB/Dipole or F12G subs. His main business is DIY speaker kits and subs; you make the enclosure (or buy it from Parts Express, Meniscus, etc.) and assemble the x/o (parts provided), then install the kit's drivers, the x/o board, and the internal stuffing into it.

Rythmik offers some of it's subs as kits, and it is those kit-version Rythmik subs that Jim Salk installs in his incredible real wood veneer enclosures. Take a look at the bracing design he came up with! It's a honeycomb-type construction, the best bracing I have ever seen in a sub. Danny Richie's F12G design is great too---double-walled, the space between the walls filled with sand. Reminds me of those big speakers from the 1950's that did the same. Was it Bozak? Wharfdale? 

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.