Axiom Home Page Forums General Discussion Technical Questions Comments? Monopole vs. Multipole Editorial

I came across this commentary on the use of Dipole speakers as surround speakers, and thought it would be of interest.

Before we begin, please note that I don't necessarily agree with this person's argument--I'm merely using it as a discussion spark.

From www.adnm.com in the "Advice" section.

In reply to:

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A word on Dipole Speakers

Nothing infuriates me more than blanket recommendation of dipolar speakers with no serious discussion of their limitations and flaws. Dipole speakers were designed specifically to hide the poor rear channel sound of Dolby Pro-logic surround. In Pro-Logic, the rear channels are monophonic and extremely low fidelity, essentially equivalent to AM radio. The thought was to make take the monophonic sound and spread it across the back of the room to make it more spacious and less noticeable. However, with the advent of 5.1 soundtracks with essentially CD-quality stereo rear channel sound, spaciousness is dramatically improved and, because of the dramatic improvement in quality, there is no reason to hide the rear sound any more. And, with the ability to further split two rear channels into three, precision and spaciousness are enhanced to levels no dipole speaker could possibly match. Interestingly, dipole speakers are the most difficult to setup because there is only one way to set them up at all - directly to the side of the couch, several feet above the listening position with the couch 5-10' from the back wall. Any deviation from that setup yields even lower quality rear channel sound. Also, many proponents back dipole speakers because "it mimics the more diffuse sound of a movie theater." This is like buying a sports car that performs like a bus. Movie theater sound is awful compared to a good home theater system. More to the point, sound engineers use two or three discrete directional speakers behind them, not dipoles. If you want to hear what the sound engineer hears in his mixdown studio avoid dipole loudspeakers at all cost. Movie theaters sound the way they do because they have to play decent sound to hundreds of people, where as a home theater can focus its performance on just a few people. Also, many dipolar proponents insist that dipolar speakers are less noticeable and allow you to concentrate more fully on the TV screen "as the director intended". But they don't know what the director intended.. Dipolar sound is an "effect" that seriously modifies and dilutes the sound of the rear channels. Only true monitor speakers allow you to hear exactly what the sound engineer heard when he mixed the soundtrack. If he mixed for a diffuse effect, that is what you will get. If he wanted an intense, distracting effect, that is what you will get. If you own dipolar speaker and want to understand more of what I mean, hook them up to the stereo front channels of your receiver and play stereo music through them. If that doesn't convince you of the low fidelity of dipolar speakers, I don't know what will. Although I could go on forever on the dipole subject, I can say that we have switched dozens of people out of dipolar rear speakers purchased elsewhere because the customer simply did not get the performance that he had expected from their new DVD player. All of them are extremely happy with the far more accurate and intense surround sound of high quality monitor speakers.

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This editorial contains way too many absolutes for my tastes, but I think there is some substance to the argument. It seems that this discussion is relevant to all multipole applications--not just dipole. What do you QS fans think? How about those using M2s, M3s and others for their surrounds? I especially invite some commentary from Alan on this subject.

One book-length post deserves another...

First let me differentiate between "rear" and "surround" speakers in regards to a 7.1 setup. I think, from what I've seen on this board, that the opinion of the majority is:

Diffuse radiating for surrounds, direct for rears. I don't personally have a 7.1 system, what I do have is a sub-ideal room layout with a 5.1 system.

So I will speak to the case of 5.1 with the surrounds being what this author calls rears. I previously had directional surrounds, when I got the QS8s I immediately felt that when watching movies the surround effects were more enveloping. An example of how this "enveloping" manifested itself:

Imagine a movie scene where the main character is moving through a jungle and some bird overhead is being it's usual noisy bird self. There is something akin to this in many many movies so I'm not going to bother with any specific one. With my directional speakers, birds of that sort always sounded essentially like they were coming from a particular region of the room between the surround and corresponding front speaker depending on how the effect was done. With the QS8s, that region gained "height" significatly as more of the sound ultimately reached my ears after bouncing from the ceiling.

When he says that you should place your surrounds as mains and listen in order to see how much the sound degrades, he is completely missing the mark. Most of the effects in movies used to give a "surrounding" sense are ambient noises that are not naturally caused by directionally radiating sources. It makes little sense then to send them to directionally radiating speakers.

Now then for music:

In stereo listening the recording engineer attempts to present the sound in a way that acurately represents some arrangement of musicians on a stage in from of the listener. This is inherently a directional source, and I don't think anyone would realistically argure that you should place non-directional speakers as your mains. When you bring surround speakers into the mix however, they are often used to represent the acoustic effects of the recording space. Thus the sound engineer is trying to represent reflections of sound that would be reaching your ears from all directions by mixing them into a discrete set of channels. Does everyone in their house place those channels at the exact same locations with respect to the listener as they were originally placed? Was the engineer able to accurately represent the sound in the first place? He is ultimately right that you will not hear what the sound engineer hears. But will it sound worse? From my personal experience thus far it sounds significantly better.

I would also point out that the QS series is not dipolar; it is bipolar (or quadpolar, whatever). In other words, the drivers are all in phase, unlike dipoles, where the drivers were out of phase. FWIW.

badger, this is one question i DID ask Ian.
Does Ian prefer the QS8s or the direct speaker design for surrounds (even with music)?
The answer was, hands down, the quadpole QS8s.

Wow, you just get the sense that somebody pissed in that reviewers corn flakes the morning he was scheduled to write the diploe review. I'm just glad Mother Theresa wasn't on the schedule that day.

I put little faith in any paragraph that long.

Having just received my QS4s, I felt the need to chip in on this.

Dipole: the drivers are out of phase with each other intentionally. Engineers claim one of two reasons for setup this way:
1) causing phase cancellation at the heading angle - ie: if the QS series' were dipolar, this would happen where the nameplate faces you. Since some people (BigJohn, Ray3 ) have complained sometimes I don't make sense, I'll break it down. In other words, where one driver is 'pushing' and the other has its polarity reversed so it's 'pulling', where the sound waves cross, very little sound is heard. The reasoning is that you would aim the dead spot towards the listening position and not hear anything directly. The idea isn't new by any means, when I was in high school, a few of us were into the science behind speakers - I'd built a pair of 2-way 6.5" bookshelves and a centre - I'm surrently using the centre in my HT, another buddy built towers (floorstanders to those younger than 18 ), a centre and dipole surrounds (similar to the QS series in the shape, but they were deeper to get the required enclosure size for his drivers, remember, this was 1990 when you needed a driver per octave ) and I'm sure 15 years later that if I saw him on the street today, he'd tell me that "he's nearly got them set up perfectly".
2) the other reasoning was to play the phase game in the old DolbySurround/ProLogic days of mono surround to "spatialize" the signal. Much like Ozzy's vocals, things sound bigger, closer, farther away, or heavier depending on the phase (and doppler effect) and delay added to them. (and if you can't hit a note, throw a flange on for good measure)

Bipole: Bipole speakers are multiple drivers wired in phase. Ian's quadpole QS series are technically bipole wired, but he's introduced a new word to describe that there are four planes of sound on his design (versus two on traditional bipoles where the tweeters and woofers would be on the same face). Since you don't have to try to account for every angle of sound refraction and reflection with the 4 in-phase drivers when mounting, added to Axiom's drivers' off-axis response, mounting them is a matter of "just put them somewhere and they'll sound good"

As for the author, I think he's right that dipoles are past their time, they were a band-aid solution for mono surround, and I'm sure if you specifically built a room around your surrounds, you could do incredible things with them. But he's pushing people towards direct radiators, which, in my opinion (and opinions are like buttholes, everyone's got one!) are the weaker choice for home theatre applications. For me, it was like a highway drive... eyes focused a mile down the road, snapping quickly to focus on a bug carcass on the window, fighting to focus on the road again... I heard the surrounds, I could close my eyes and point to them, I had to fight to listen to the dialogue.

Bren R.

Scott, in my view most of that commentary does apply only to dipoles rather than multipolar in-phase speakers such as the QSs. These appear to be a good compromise between "diffuseness" and "directness" and are easier to position and sound better on a wider variety of material than either dipoles or monopoles. As I and others have commented previously, if a musician or other sound is specifically located in a discrete surround channel(e.g. some pop SACDs and DVD-As)a monopole can locate that sound a bit more clearly. The majority of other sounds(including the ambience which is present in the classical CDs which I listen to)benefit from a more widely dispersed presentation which still sounds reasonably good on specifically located material.

Monopole speakers are great if you have an ideally shaped room and only one person listening. I'd like to find out where that writer would put monopole speakers in my room with the TV in the corner and couches at 45 degrees to each other (picture posted in HT forum earlier this week).

It's be interesting to be able to compare dipole, bipole, and di/bi speakers. I know some manufacturers offer a switch on the speakers, but I decided to trust the reviews and go with the Axioms. I'll find out whether I like them next week.

Bruce

Hi badger98,

The writer is correct in noting the development of dipole radiators to compensate for the old Dolby Pro Logic surround channels, which indeed were mono, and, if you happened to sit equidistant between a pair of direct radiatior surrounds, would often image the surround material in the middle of your head--very annoying, to say the least.

So THX (Tom Holman) recommended dipoles located at each side of the listening area, which produced a "diffuse, directionless" effect when you sat in the null area (your couch). This greatly reduced the problems of the mono surround channel. THX processors also introduced a "decorrelation" circuit that artificially created a quasi-left and quasi-right "stereo" surround signal. That also helped.

The writer is correct in that dipole surrounds are no longer required (nor is decorrelated information in the surround channels) because Dolby Digital/dts both deliver 5.1 discrete channels of full-fidelity sound. (the frequency response of old DPL systems rolled off at 7 kHz in the surround channels).

The QS8 drivers wired in phase qualify it as bipolar or "quadpolar" speaker, as has been noted. In comparison tests we did at Axiom between quadpolar QS8s and direct radiating surrounds, if you sat exactly in the sweet spot, there was little or no perceptible difference (insofar as one being "better" than the other) between the QS8s and forward-radiating surrounds. BUT, as soon as our listening panel members moved out of the sweet spot and sat anywhere else in the room, even to one side of the couch, the QS8s were judged and ranked greatly superior (these were double-blind tests).

The writer is also wrong in stating that Dolby Digital sound in cinemas is "awful." Sometimes it can be excellent; it depends on the theater. And of course you can often achieve superior performance in a domestic home theater where you can control not only your seating arrangement but the exact locations of the speakers relative to your seat.

The virtue of the QS8's multipolar dispersion is that it makes the speaker very forgiving of asymmetrical placement, and it nicely mimics the mix of reflected and direct sound that indeed was intended by engineers mixing movie soundtracks. In fact, I've heard the QS8s deliver an enveloping surround field when placed in far-from-ideal locations.

I've attended movie soundtrack mixes in the Alfred Hitchcock mixing theater at Universal in Hollywood, as well as sessions in New York, and I can report that the director and sound engineer precisely adjust the surround channel levels to achieve envelopment with some directionality. But there seems to be a consensus that "hard-mixed" surround effects should be used sparingly, such that they should never distract your attention from what's happening on-screen. After all, the idea is to enhance your involvement in the drama and sense of place occurring on-screen. Anything that removes you from that experience is deemed to be distracting. Plane and spaceship flyovers are fine, as are off-screen sounds like crickets, crows, lightning (if a thunderstorm is in progress), and an off-screen knock on a door. Moving vehicle sounds also work well, and artillery from all directions seem entirely appropriate in war movies.

Likewise, I would submit that for multichannel music purposes, the greatest effect is achieved when you are swept up in the musical experience. If your attention is distracted by a backup chorus mixed "hard right", it's an interesting effect, but unnecessary in my view. This is where things get controversial.

Personally, I don't want to feel plunked down in the center of the band, but I admit there are certainly occasions with lots of pop-music mixes where anything goes. I do draw the line, however, at mixing Neil Young's vocals into the rear channels!

Regards,