Wendell Diller: "You don't wanna put a subwoofer with a Magneplanar; it doesn't work."

In an interview with Chris Martens of The Absolute Sound and Hi-Fi + (viewable on YouTube), Magnepan’s head of promotion Wendell Diller (he is also involved in product development) discusses the company’s upcoming new product: the Ultra Wideband Bass System (UBS). Though the thread heading quote (taken from the interview) would lead one to assume the UBS is not a sub, it in fact is. Huh?

Wendell is of course referring to all "normal" subs, normal meaning sealed and ported enclosures with dynamic (cone) woofers. Sorry REL enthusiasts, that includes yours. ;-) Wendell goes on to say:

"’Cause you’re mixing a monopole with a dipole." Long term Audiogoners may recall I (and a few others) have been singing the praises of the GR Research/Rythmik Audio OB/Dipole Servo-Feedback Subwoofer for a few years now. I have been especially adamant in opining that this particular sub is THE sub for any and all dipole loudspeakers, and have given the technical reasons why such is the case. I won’t repeat it here, as I grow weary of wasting my time. For those seriously interested, a search of old threads will reward you with my wisdom. ;-)

Wendell goes on to say: "A dipole woofer is not a new idea." Indeed not. Danny Richie of GR Research was already designing loudspeakers employing dipole woofers (and dipole midrange and tweeter drivers) and selling them as DIY kits when he heard about a new servo-feedback subwoofer (again, not a new idea. At least in general terms.), one being offered by another company located in Texas: Rythmik Audio. Rythmik’s Brian Ding had designed (and patented) a new method of applying feedback to a woofer, and Danny proposed the two of them put their big brains together and develop the world’s first OB/Dipole subwoofer to include servo-feedback. Few have heard it, but I’m tellin’ ya, it was a game changer. Wendell and Magnepan are late to the party (they are not alone. Read on.), but better late than never.

I and other early Magneplanar Tympani owners (I bought my T-I’s in 1972) were permanently spoilt by the quality of the bass reproduced by those big bass panels (two 16" wide x 6’ tall panels per channel). I recorded my 26" Gretsch bass drum with a small capsule condenser mic plugged directly into a Revox A77, and I have never heard a cone woofer reproduce the sound of that bass drum as do Tympani’s (I now own a pair of T-IVa). Those bass panels are also unmatched when it comes to the lower registers of a grand piano, an upright bass, and in fact all low-frequency percussive sounds. Even the "shudder" produced by the massive organ pipes heard in cathedrals and churches. Tympani bass panels are also unmatched at reproducing the "texture" of bass instruments.

Magnepan now offers the incredible 30.7 (I heard it when Wendell took it "on tour" a few years ago), which is an updated version of the Tympani’s. But Wendell himself no longer has a room big enough for a pair of 4’ wide panel loudspeakers, so embarked on a development project to create an alternative. The result was the concept loudspeaker, temporarily referred to as the "30.7 For Condos". It is the midrange/tweeter panel from the 30.7, with a new dipole subwoofer in place of the huge 30.7 bass panels.

This Magnepan dipole sub will be made available for augmenting all the company’s loudspeakers, in a number of driver incarnations. The debut model incorporates 8 woofers per sub (I’ve heard either 6.5" or 8" woofers), the drivers powered by an on-board amp, with crossover and DSP facilities. Wendell: "This concept really works because of DSP. With DSP you can fix the time/phase/amplitude problems so it plays nicely with whatever the panel might be." Not to be contrary, but the Rythmik Audio A370 plate amp that is included in the GR Research/Rythmik Audio OB/Dipole Subwoofer provides controls for optimizing the time/phase/amplitude relationship between loudspeaker and sub, and does so without any digitization of the signal.

Wendell: "I see this dipole as the proverbial fork in the road for Magnepan because it can keep up with any of the panels. This concept is unique." Uh, ’fraid not Wendell ;-) .

Ya know, Magnepan is not the only maker of magnetic-planar loudspeakers in the world. Bruce Thigpen of Eminent Technology, though very impressed with the Magneplanars, thought he could improve on them. Bruce developed his own m-p driver, imo better designed and built than those of Magnepan (I have both). His LFT driver is a vast improvement on the design still used by Magnepan, but to keep the size of his LFT-8b loudspeaker "manageable" he compromised by using an 8" woofer installed in a sealed enclosure to reproduce 180Hz downward.

Great minds think alike? ;-) Already available from ET is Bruce’s new dipole sub, also employing DSP. ET’s sub is being called a dipole, but I don’t know whether or not it is an OB. The sub is a bolt-on replacement for the stock LFT-8b sub, and retails for $1500/pr. The LFT-8 shipped with the new dipole sub is named the LFT-8c, and it retails for $3999. So an owner of the 8b (which originally sold for $2499, now $2999) pays no penalty for now buying the sub to use with that models still-identical m-p panels.

For planar loudspeaker owners who crave full-range bass, but both lack the space necessary for huge planar bass panels and find monopole subs unsatisfactory for use with planar loudspeakers, you now have options. The GR Research/Rythmik Audio Servo-Feedback Subwoofer is killer, but is available as a kit only. The required OB frames are available as flat pack, and are simple to assemble and paint. But for those who want plug & play, the Magnepan UBS is certainly good news. As is the ET dipole sub for current LFT-8b owners. For planar loudspeakers owners who find monopole subs fine with panels, either Wendell Diller is wrong or you are. ;-)


Hi Russ,

Someone told me that the LRS+ is there but hard to find. They seriously need to work on their website!

JKF011, you have mid sized Maggies. The big ones go much deeper and have more punch. (Bass performance also depends very much on the room -- swings of 20 dB are common. If you listen to the larger Maggies, what you'll hear is bass that's *realistic* in the way that two monopole woofers, no matter how good, aren't. To get that kind of sound from monopole woofers, you need four to reduce the excitation of room modes.

Anyway, the goal of the Magnepan woofers is to combine dipole realism with dynamic "slam" and by all accounts, they've hit a home run -- everyone who has heard it has been enthusiastic -- Chris Martens of The Absolute Sound says it's the best woofer he's ever heard. (Disclosure: I don't work for Magnepan and have never received any money from them, but I did have a role in the development of the new woofers. What I'm passing along here are some of the considerations we used in designing them, as well as the results of our experiments. We were surprised to find, for example, that multiple small drivers sound better than a large one with equal displacement -- others in the business have made the same observation. Some of this is probably due to behavior in the crossover region -- that's known to make a woofer sound "slow" if the drivers don't match -- but there are likely other factors as well.)

I run a pair of small MLs with mine to decent effect. Ideal? Probably not, but with careful adjustment, quite good.

I would expect WD’s woofer/subwoofer integration to be much better than the many trials of past integrations.  Looking forward to a demo.

@josh358: Great post at 11:01 am (and 11:12 too)!

You make an important correction to my saying (in my explanation of dipole cancellation) that bass frequencies are omnidirectional. As you state, it is not that bass frequencies are omni, but rather that sealed/ported subs behave as omni sources because of the woofer enclosure dimensions vs. bass frequency "dimensions" (much larger than the enclosure. In fact, much larger than most room dimensions). This topic requires more time and space to fully discuss than most would care for (again, Siegfried Linkwitz’s writings on the subject are readily available for those interested), but there are a couple of points I would like to make:

One of the benefits of dipole loudspeakers is their radiation pattern: the aforementioned figure-of-8. At higher frequencies that side-speaker null (the dipole front and rear waves meeting on the sides, and due to opposing polarities cancelling one another; +1 and -1 equal 0) greatly reduces the problem of side wall reflections. The QUAD 57 (and the Sanders ESL loudspeaker) is well known to be a single-person loudspeaker: the speaker needs to be pointed directly at the listener, as its frequency response takes a dose dive as you move off axis).

At bass frequencies, those nulls almost-entirely eliminate the excitation of room modes in the room’s left-to-right axis. Fewer room modes = less "room boom". On the other hand, as Josh points out, that dipole back wave creates a problem that non-dipoles don’t (at least not to the same degree): the rear wave (half of the loudspeaker’s output) reflecting off the wall behind the loudspeaker and traveling back to the panel, where its phase relationship with the front wave can cause either frequency reinforcement, or instead cancellation. Ay carumba!

For that reason, dipole/front wall distance experimentation is required to optimize sound quality. But you audiophiles are use to and expect that, right? ;-) But here’s a basic rule: if at all possible, a dipole should be no closer to the wall behind it than 5’, minimum. Why? Because 1- sound travels at approximately 1’ per millisecond; 2- for two sounds to be perceived as separate events, they need to be separated in time by at least 10ms. At a dipole/wall distance of 5’, the dipole rear wave travels the 5’ to the wall behind it, then the 5’ back to the dipole, where it is now separated in time from the front wave by the 10ms required for the two waves to be perceived a separate entities, rather than the rear wave being a "smearing" of the front wave. Dipole 101. ;-)

Dipole cancellation occurs on both left and right sides of a dipole, and results in reduced SPL output. Danny Richie (GR Research) and Brian Ding (Rythmik Audio) advise that their OB/Dipole sub produces 1/4 the output (fed the same signal) as the same driver installed in a sealed enclosure. The answer is of course to use more of them. Hey, its only money, right? ;-) Some fanatics use GRR/Rythmik OB subs stacked floor to ceiling.

The dipole cancellation phenomenon can be tailored in a number of ways. In the old days dipole designers/builders used a wide baffle (in the DIY world that remains common), the dimensions of which would determine the frequency at which cancellation would occur: the greater the distance between the front and rear drivers, the lower the frequency at which cancellation occurs. Danny Richie found an unbraced large panel to be sonically unacceptable (he is very intolerant of resonances), so uses the same style H-frame to house his dual 12" woofers as did Siegfried Linkwitz with his dual 10’s (to see an H-frame is to understand why it is named that). Both designers settled on roughly the same H-frame dimensions: deep enough to lower the cancellation frequency to where they wanted it, but shallow enough to make the resulting cavity resonance occur at a frequency above the passband of the sub (in the GRR/Rythmik, 300Hz). Linkwitz’s H-frame is constructed of a single layer of 3/4" MDF, but Danny---the perfectionists that he is---specifies 1-1/2"

Magneplanar Tympani enthusiasts long ago discovered that if you position one side of the Tympani bass panels right up against a side wall, you would prevent dipole cancellation on that side, resulting in increased SPL output. Another means of increasing the panel output is to brace them to the room structure, often to the wall behind them. Yes, hardcore Tympani enthusiasts are a fanatical bunch (Hi Josh ;-) .

When sold for use in the OB/Dipole Sub, Brian Ding installs in his Rythmik A370 plate amp a "Dipole Cancellation Compensation Circuit". It is basically a filter which is a mirror-image of the roll-off endemic in the OB/Dipole’s output characteristics, which allows the sub to reach quite low in frequency, at relatively-high maximum SPL capabilities. Not Rock ’n’ Roll concert levels (I saw NRBQ in a medium size club last night, and it was pretty damn loud. Not Ramones !LOUD!, but loud), but as much output as most of us need (want is a different matter ;-) .

I of course don’t yet know how the upcoming Magnepan dipole woofer sounds, or for that matter the OB from Eminent Technology (Bruce also offers a "true subwoofer", for the frequencies below 20Hz!). But the GR Research/Rythmik Audio Servo-Feedback OB/Dipole Sub is a hard act to follow. I just wish I had a room big enough for the Tympani bass panels, as they require no augmentation (well, unless you need 30Hz and below), and remain my low frequency reproduction yardstick. The GRR/Rythmik OB/Dipole comes closest to matching the Tympani bass panels as any woofers/subs I’ve yet heard, far better than the woofer towers of my now-sold (back to Brooks Berdan, from whom I bought them) Infinity RS-1b’s (also a servo-feedback design).