Image Is Everything

There aren’t too many to choose from, but bipole and dipole speakers are a special breed that I've long admired.

We just posted our review and an inside look at Definitive Technology’s recently revised BP9000 series. The BP9080x towers represent the fourth generation of the product that launched the brand in 1990, the BP10, a passive tower featuring a bipolar radiation pattern (powered woofers were added later). Many of us have heard or own bipole or dipole surround sound speakers. These typically have a pair of offset baffles and can provide a more diffuse and less localizable rear soundfield to enhance the sense of envelopment. But bipole and dipole mains, used in the front left/right positions of a stereo pair, have always been a bit of a rarity; perhaps more so today. I’d venture to say that many of our 90,000 readers have never actually heard a well-optimized bipole or dipole speaker pair backed by good electronics and source material.

That’s a shame, because they’re something to behold.

For those unaware, bipole main speakers emanate sound from both the front and rear, with the rear-projecting sound in phase with the output coming from the front. This means that when the direct-radiating front drivers are pushing out or pulling back, the rear-facing drivers are doing the same. Dipole mains similarly project from front and back, except the sound coming from the back is out of phase from the front, with the diaphragm direction equal but opposite that of the front-facing drivers. Flat-membrane speakers, such as electrostatics or magnetic planar designs, are usually open at the back and create a dipolar radiation pattern.

The reason for taking this approach, of course, is that it can enhance the soundstage and imaging in a very noticeable way. When you simultaneously send sound away from the listener like this, you automatically make your room, notably the back wall behind the speaker, part of the design. In the right room, with an optimum amount of space behind and around the speakers, bipoles and dipoles can use those reflections to deliver a crazy wide and deep soundstage, inhabited by near lifelike (if not bigger) voices and instruments. The trade-off, at least from a practical standpoint, is said to be somewhat less focus of the voices and instruments inside that soundstage.

In the right room, with an optimum amount of space behind and around the speakers, bipoles and dipoles use reflections to deliver a crazy wide and deep soundstage.

So in a way, it all comes down to a matter of taste—a point that’s well made by Dan Kumin at the end of his BP9000 review. Not too long ago, I wrote about how better speakers tend to target the same goal of neutrality but still retain their own signature. Part of that is from differences in how they image. At various times in my hobby and career, I’ve been lucky enough to own Dahlquist DQ-10s—a now legendary speaker that used multiple, staggered open driver arrays on time-aligned baffles to enhance the soundstage; a pair of MartinLogan CLS electrostatics; and the Magnepan MG-I, a tall magnetic-planar dipole. Each had its weaknesses, but each had, as its great strength, the ability to create a lifelike, three-dimensional soundstage that sucked me in at the first note.

I was reminded of that recently when Definitive demo’d the new BP9040 for me in a hotel suite in New York. Despite a less than perfect room, they sounded great and...big. And I was heartened that, in this age of ever-shrinking wireless box speakers fed by smartphones, we still have a few affordable options for audiophile-quality bipoles and dipoles from the Def Techs, MartinLogans, and Magnepans of the world. That Definitive Technology continues to evolve and improve these BP towers 26 years after their introduction is a testament to what is fundamentally right and musical about them.

markymo32's picture

In 1968 Bose released the 901 series I which send 89% reflected sound against the back wall and 11% direct sound into the room This speaker is still produced today but on its sixth series...901 VI

brenro's picture

Sandy Gross has made a career from stealing Mirage Speaker's bipole technology. Let's try and give credit where it's due.

geickmei's picture

Your general comment that dipole and bipole speakers have less focus for the soundstage is not true. You can screw up the focus by mis-positioning the speakers or having too much clutter at the speaker end of your room, but if you can achieve a dedicated listening room with specular reflectivity at the speaker end then you will have spectacular focus and depth and spaciousness. Speakers should be positioned for imaging, not frequency response. Place them 1/4 of the room width in from the side walls and out from the front wall. This placement will focus the reflected sound so that it will enhance, rather than detract from the soundstage focus. In Daniel Kumin's test report on the BP9080X speaker he tells us how far out from the front wall he placed them, but says nothing about the room size or how far from the side walls. I looked in your "How We Test" and it also says nothing about your test rooms. Very important!

Sandy Gross's picture

When I read the posting by brenro, I was quite taken aback, both by the attempt to reduce my 44 years of hard work and success in the audio industry (and by inference Definitive's success as well, both before and after I left), to "stealing Mirage's bipolar technology", as well as looking at bipolar speakers as my only achievement. I'm not sure if this vicious and unfounded attack was purposeful in that way, or just the result of a lack of historical knowledge, so let me assume the latter. First, let me address the concept that I stole the concept of bipolar speaker technology from Mirage.
Just for reference, Mirage was a Canadian loudspeaker company that began around 1979 and introduced, what they called a "bipolar speaker", the M 1, in the late 1980s. A bipolar speaker ( yes, that was a new term introduced by Mirage, but certainly not a new concept) radiates in-phase information, both forward and rearward, as opposed to a dipolar speaker that radiates sound forward and rearward out of phase. It is, in effect, more like an omnidirectional speaker, radiating sound in 360 degrees, rather than the radiation pattern and imaging of a dipolar speaker, which radiates sound in a figure eight pattern, basically no sound to the sides or directly up and down, because of cancellation between the front and rear radiation from the speaker. Just for the record, when we started Polk Audio in 1972, the first speaker that Matt Polk and I jointly created, in 1973 or 1974, was a bipolar speaker called the Model Nine Controlled Dispersion Array. No, we did not call it a bipolar speaker, but it clearly was one. I suppose in terms of further describing it, it was a narrow tower, with drivers front and rear (similar to the later BP 10), in an attempt to duplicate the radiation patterns and sound field produced by our references of the day--the Quad 57 and KLH 9. There were an unequal number drivers from and rear, so it was, in effect, an asymmetrical bipolar speaker (a term Energy coined), as the current Definitive bipolars are, and as the Energy Audissey bipolar speakers were (circa 1998), delivering unequal sound forwards as rearwards. While the new Definitive and Energy Audisseys deliver(ed) more sound forward than rearward, the Polk Model Nine delivered more sound rearward, than forward, although it varied with frequency. Matt and I worked hard on the Model Nine, the first Polk Audio home loudspeaker, and it was successful.
I would not say that Mirage copied our concept, as I don't know if they were aware of the Model Nine, however they do seem to have been aware of some of the more unusual speakers of that era, as their later "Omnipolar" speakers bore a striking similarity in concept and execution to Stuart Hegeman's Hegeman 1, which was produced in the 70s, as was the Polk Model Nine. But I can say that when we launched Definitive in 1990, we decided that when starting a new company, we were in a position and free to return to a concept that I pioneered in the early 70s in the Model Nine.The BP 10, that we introduced in 1990, was not, in any way, a copy of the Mirage M 1, which was very wide and had a completely different array and combination of drivers. In fact, if you look through subsequent products by Mirage, you will see that Mirage later introduced a speaker, the M-895i, that was very close to a virtual copy of the BP 10. Enough of this. Clearly, the bipolar concept and execution that I introduced in 1990 at Definitive, was excellent enough that it could be continued and successfully developed for the ensuing 26 years, both by Don and myself when we were still at Definitive, and then by those there after we left. In terms of other successful new concepts that I was involved in launching, let us not forget the introduction of the concept of built-in powered subwoofers, which Don (my partner again at GoldenEar) and I introduced in 1995 in the BP 2000. This was copied in the day by virtually every loudspeaker manufacturer, and then more or less abandoned by every one except Definitive, and of course, introduced by GoldenEar in our Triton Towers, as it is something that we personally pioneered and really believe in. Interestingly, the concept of built-in powered subwoofers, or actually built-in powered bass sections that extend into the sub-bass, has in recent years been incorporated into some rather expensive and well received high-end loudspeakers produced by Vandersteen, Martin Logan, Lansche, Paradigm, Avantgarde and Steinway Lyngdorf, among others.
Now back to the poster's remark: clearly at GoldenEar, launched in 2010, we do not make bipolar speakers, and find it hard to see, in any way, how this portion of my career (six years at this point and still going), also quite successful, has anything to do with bipolar speakers, as the poster seems to imply. Perhaps the poster is just not aware of GoldenEar and what we do. For the record, Don and I, some years ago, realized that our knowledge base regarding speaker design had come a long way since 1990, when we introduced bipolar speakers in an attempt to enhance imaging. When we started GoldenEar and began designing our products, we felt that although bipolar technology could "enhance imaging"; if properly designed, a direct radiating loudspeaker could deliver as large, or a larger image without "enhancing" or manipulating it, and, at the same time, can deliver a superb soundfield with greater clarity, improved depth retrieval of the information actually on the recording and fewer problems with achieving proper room placement and avoiding deleterious room effects. If you look at very high- end loudspeakers, selling for 20K, 40K, 80K, 100K, 200K... a pair, you see few, if any, bipolar speakers, but rather a focus, as we have followed at GoldenEar, to deliver all the information on the recording, with no changes or enhancements, pure and simple. You do find dipolar speakers, but in reality those are of a different nature, radiating sound forwards and rearwards as a consequence and result of their transducer technology, rather than as a specific design decision and goal, as it is with bipolar speakers. In fact, one of the challenges with dipolar speakers, is setting them up so that the rear wave does not interfere with the front wave, and one manufacturer of superb dipolar electrostatic speakers, SoundLab, actually offers a special accessory specifically designed to absorb the rear wave. I am gratified that Definitive has continued to develop the speakers that Don and I introduced and refined in our tenure there, and I am sure that they are excellent. But we have evolved and gone in a different direction, as I have described, and have been extraordinarily successful at it.
So, relative to this insulting posting, that has incorrectly insinuated that my career is based on stealing Mirage's technology, I certainly think that this is both incorrect, in its simplest sense, and clearly demeaning in terms of my life's work, and I felt that I did have to respond. Sincerely, Sandy Gross

canman4pm's picture

Well said, Mr Gross. Remember: Trolls are...

PS: I (and I'm sure I'm not alone) love and appreciate, your work. I wish I could afford to buy a 6-pack of Triton Ones to build a theatre around. Maybe some day. Along with a quartet of in ceiling speakers and an 7.1/2.4 amp worthy of the lot.

profdbb's picture

Sandy: It is a shame that you have to post a response. I am in my fifties and have owned many speaker brands, including Magnepan, KEF, NHT, and even a pair of Altec Lansings. I remember when your first BP10s hit the market. There was no talk at the time that you had stolen the idea of bipolar speaker technology (and stereo magazines at the time could be pretty snarky). There was an intense debate among audiophiles about the relative strengths and weaknesses of bipole v dipole. There is a tradition of innovation in audio finding its way into many products, and your use of powered woofers is an example. For example, there are several manufacturers using concentric tweeter/midrange drivers, and I do not think I have heard a serious comment that one company has stolen the idea.. I suppose that in some instance, if a company has actual patent rights, things would be different. I should also point out that you introduced your DR series of direct reflecting speakers when you first produced the BP10s(I bought a pair of DR towers, which I still have, so you have experience with a more conventional approach to speakers. And I do not see anyone suggesting that you stole direct reflecting technology (as that would imply that virtually every speaker maker has done so.) One last thing. Just before buying my DefTech speakers, I had a question about obtaining a white speaker cover that my retailer could not immediately answer. I called your company, and you picked up the line and answered my question. I think that should pretty much indicate your care for customers and dedication to your business. Thank you for your work.