Magnepan 20.7 and Subs

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? 

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.

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 ;-) .

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.

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.