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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. ;-)

128x128bdp24
audiokinesis
2,723 posts
 

James M. Kates wrote an Audio Engineering Society paper many years ago (which I don’t have the reference for) showing the improved in-room bass smoothness of a dipole relative to a monopole. So if we want a subwoofer system which approximates the in-room bass smoothness of a dipole, we either need to find a way to make a worthwhile improvement over the in-room bass smoothness of a monopole, or use dipoles.

Note that "smooth bass" is "fast bass", both perceptually and literally, as it is the frequency response peaks which take longer to decay into inaudibility. Kates showed that dipoles interact with the room in such a way as to have less frequency response peaking in the bass region than monopoles do. As a longtime owner of and dealer for dipole speakers (SoundLab electrostats) and a manufacturer of monopole speakers, my experience has been that good fullrange dipole speakers have superior bass region articulation and pitch definition compared with good fullrange monopole speakers, but that good fullrange monopole speakers do a better job of conveying "impact".

Earl Geddes on the subject of how to get smooth in-room bass using monopole subs:

"The use of multiple source locations [multiple subs intelligently distributed] in the modal region will globally yield a response curve that is closer to the natural power response of the sources and the room. Said another way, if we use multiple source locations the frequency response at any given location in the room will become closer to the true power response (read smoother) the more sources that are used. Basically if I have one source which has a variance, V, of the frequency response (the variation of the response from the average or smooth response) of say 6 dBs, by adding a second source we will reduce this variance by half to 3 dB. Adding a third source reduces this to 2 dB, etc. Basically the variance goes as V/N where N is the number of “independent” sources. A key requirement here is “independent”. If the added sources are close to the first source then they are not independent. And two sources in opposite corners or symmetrical locations are not as independent as two sources placed in non‐symmetrical locations. It is impossible to have two sources that are completely independent at LFs in a small room, so the effect is never as good as the formula suggests."

Duke

dealer/manufacturer

bdp24's avatar
bdp24 OP
9,500 posts
 

@pedroeb (and @perkri): Silly boys, you missed the joke. Don’t you see the ;-) after the line you quote? I am regularly guilty of giving humans too much credit. For all I know, you don’t even understand the use of irony.

Obviously some don’t understand the significant differences between a dipole sub and an omnipole one. Do some reading, and all will become clear. Reading Siegfried Linkwitz will give you a free education.

For starters, a dipole reproduces---say 100Hz---from both the front and rear of the panel, the front and rear waves being in opposite polarity. When the waves wrap around the sides of the panel (yes, very low frequencies are omnidirectional) the front and rear waves meet, and as they are opposite in polarity their combined outputs create a null on either side of the panel. At low frequencies the polar response of a dipole sub is a figure-of-8, just like that of a dipole loudspeaker. If you don’t think that’s important, Siegfried Linkwitz disagrees with you.

Then there is the fact that a dipole sub doesn’t pressurize the room as does an omnipole; the air on both sides of the dipole is moved from one side of the room to the other, while an omni pumps bass waves into the room from inside the enclosure (a virtual room within a room). Sounds like an insignificant difference, but it’s not.

Until you have heard a dipole subwoofer, your opinion of them is based on incomplete knowledge and lack of direct empirical experience.

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kingbarbuda
514 posts
 

@pedroeb Since you mentioned him, what ever happened to @MillerCarbon? Last I saw, he was selling his Raven Audio integrated and then he disappeared. 

theaudioamp
221 posts
 

@audiokinesis if we are going to go to that level then we need to go all the way.

 

As @bdp24 points out Dipoles are much different and even as a woofer and Linkwitz is a good resource. With Mags you have both a dipole and a large surface radiator.

 

Paper referenced by @audiokinesis was from early 2000 and was not without it’s flaws. This was pointed out in a reply to the paper. Specifically the flaws were in how the dipoles would excite room modes in smaller rooms and that his 2D simulation was a poor assumption at low frequencies. Linkwitz also wrote a long comment about this and another paper along the same lines.

 

While it is true that a Dipole can provide better upper bass, at lower frequencies the lack of node excitation causes deeper nulls which are near impossible to equalize.

 

So the issue is not just whether you can integrate monopole subs, but whether you should allow dipoles to go that low period. If you take advantage of DSP for sub control you can smoothly integrate over a narrow band effectively and use monopole subs which will work better than dipoles where they are most effective.

 

A dipole sub just comes across as a poorly thought out plan for most people and one that extends at all past 120Hz is going to create imaging problems dipole or not without proving any improvement in accuracy at lower frequencies.

richopp
760 posts
 

Personally, I have never seen the need for a sub with Maggies, but to each their own, I suppose. In my shop, we would sell you whatever you THINK you need, and be happy to cash your check.

Maggies reproduce what you feed them, so I suggest you get some good "feeder" stuff and then listen. Bass from Maggies is tight and does not slam you gut like live bass at heavy rock shows where the mixer has no idea what is going on and cranks it up to 12. Whatever.

Go into the studio and LISTEN to the mix as the musicians are playing--if indeed you can find a studio that actually lets the musicians play as a BAND and not one at a time with headphones on so the engineer can "make" the music. The dynamic range of the BAND includes the bass at its appropriate volume and tenor. It is part of the total sound, and not meant to stick out by itself in the mix--disco respectively excluded, of course--and with Maggies you get good punch without overpowering the rest of the band.

BUT, if you love that gut punch, stop screwing around with those little 8-12" sissified woofers and get a REAL pair of sub-woofers : Hartley 26"’s with 1000 watt amps in 5’ high cabs and you can have it!

Enjoy!

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