Dipole Asymmetry


I am considering purchase of a pair of Martin Logan Summit X speakers. In my room, I am somewhat constrained for speaker placement. I could place the speakers about 3-4 feet off the front wall. My main concern is my audio rack would be placed directly behind the left speaker, while there would be nothing placed behind the right speaker. How detrimental would this asymmetry be on sound quality?
imgoodwithtools

If you can duplicate/imitate the scattering of the sound from the rack & components behind your left speaker with diffusion behind your right speaker, you may be all right. If not, timbral (tonality, coloration) and temporal (timing) differences between the left and right speaker may be audible.

Planars can use all the space behind them as possible, with 5’ a good compromise. 5’ allows for a 10 millisecond delay between the sound from the front of the panels and that from the rear reaching the listener’s ears (sound traveling about 1 ft./millisecond.). 10 milliseconds is about what it takes the brain to differentiate between two identical sounds reaching the ears from the same location (the speakers). 10ms results in the sound from the rear of the speakers being perceived by the brain as separate from the sound directly from their front. That reverse wave of dipoles is one of their characteristics dipole enthusiasts value in a speaker, as it (re?)creates depth and a large sound stage. Dipole users not wanting those characteristics are free to place absorption behind their speakers.

Some dipole owners lacking 5’ of space behind their speakers move the speakers out for serious listening, moving the speakers back when not listening.

I agree that is pretty close to the rear wall. Solutions would be acoustic panels from GIK Acoustics.

Also, put a panel between the speaker and the rack. It won't be ideal, but much better. :)
imgoodwithtools
I am considering purchase of a pair of Martin Logan Summit X speakers. In my room, I am somewhat constrained for speaker placement. I could place the speakers about 3-4 feet off the front wall. My main concern is my audio rack would be placed directly behind the left speaker, while there would be nothing placed behind the right speaker
If this is your setup, there's really no good reason to be considering dipole speakers, imo. Yes, there are things you could do to limit the effects of the constraints you face ... but to what end? Your space is simply better suited to a more conventional box speaker system.
Since no one this far has said Aw, shucks, just put those speakers there and they'll be fine, I must assume there will be audible differences channel to channel. I suppose the magnitude of those differences would be open for debate. I think Cleeds may be right, in suggesting a more conventional speaker design. 
And why would I consider these speakers with my room constraints? Because I want to play, Dammit! Lol
If you have a turntable, putting it directly in the line of fire could potentially cause a feedback issue. 
IMHO, to get the sound you are paying for at those price points you need absorption behind the dipoles, even more so if less than 5' distance.

If you can't do that you could try floor standing absorbers that go right behind the speaker. Warning, they are big, ugly and rare but Sound Lab makes a model and I believe there are DIY versions online. 

The best solution might be getting a longer set of interconnects and moving the rack if possible with just the amp(s) near or behind the speakers. Cheers,
Spencer
sbank
...  you need absorption behind the dipoles, even more so if less than 5' distance.
Would you please explain why you'd put absorption behind a dipole speaker, when part of the dipole concept includes reflection off the wall behind the speaker?

@cleeds time.

You need about 15 ms between the direct signal and first strong reflections so your brain builds up the image and tonal characteristics of the music without significant blurring and smearing.  At about 1ft per millisecod, 5ft x 2 = 10. Too short a difference.

@erik_squires
you need about 15 ms between the direct signal and first strong reflections ...
I get your point about that. I still don't see how absorption behind dipoles would help, unless the reflection was excessive.
Tell us more about your room and your amplification.  It doesn't sound like you have the option of placing the Summits optimally, but more info will help.
@cleeds Sorry my friend, i may be a little brain fogged right now.

If the speakers are less than 8' or so from the rear walls, the reflections would occur before 15 mSeconds.  The idea is to reduce as much as possible all reflections within the first 15 mseconds. Panels behind the speakers will do this, to some extent. It won't be perfect, but reduced.

If I'm still being unclear I'm sorry.
And why, I think, I will shy away from the dipoles. My B&W speakers attempt to dampen rearward energy. And they do sound great in my room and setup.
My room and curent setup are as follows:
13' x 38' x 8.5'H. Rear half of the room is a pool table area. Front half is the stereo
side. Speakers are placed about 3' from the front wall to the rear of the speakers. Speakers are 7.5' apart. 9 ft speakers to listening chair. Audio stand directly behind the left channel speaker. 60 in flat screen TV on the front wall. Amps are Ayre MX-R Twenties.
@imgoodwithtools Nice setup!
Thanks! It's a decent man cave. All I need is a stripper pole. Lol
@imgoodwithtools


Good way for you to loose weight! ;-)
Post removed 
If it were me I wouldn't worry about it too much. You could try putting a diffuser panel (as opposed to absorption) behind the other speaker to even out the reflections compared to the rack. The GiK suggestion is a great one. If it matters (to you), they even sell real nice DIY kits to save a few $.

I think that many people get great sound from MLs placed 3 or 4 feet out from the front wall. Martin Logan recommends 2 to 3 feet. I don’t think having your rack behind one speaker would be that big a problem. You can experiment with diffusion on the other side, a cd rack or a diffusion panel or something else. You don’t need technically ideal conditions for the MLs to sound really good.

You can find the owner’s manual on their web site and see what they have to say about it, and you can probably call ML and talk to someone about it.


imgood, tomcy6 has a point, and a simple solution to my mind.  Try duplicating the approximate shape of your left rack behind the right OR put panels behind both.  With the first, you mess a little with the diffusion behind the speakers.  With the second, you simply reduce the delay time.  You might try both just to see the difference and which you'd prefer.

I have dipole ribbons (Heil AMT's) 2' from the wall...sounds good to me. *G*  Lucky to have 'blank walls' behind though...
This is audiophile neurosis at its best (worst) .If in a blind test anyone could hear which side had a rack and which side did not deserves the worlds "best ears award" . 
With this mindset, Maplegrove, do you also believe acoustic treatments or tube traps offer no merit? How about speaker placement?
@maplegrovemusic

Compared to cables, fuses, etc. NOTHING measures a bigger improvement than acoustic treatment. 

Honestly though in this case the much bigger issue is putting di-poles so close to the walls. Fixing or compensating for that part first would be my first priority, second dealing with the bass response, third the rack.


Best,

Erik
Of course, there are simple things to try. I would turn my rack sideways and cover it in a courtain. :)
imgoodwithtools - look at my system page for an answer about how i feel about room acoustics .I believe room acoustics is the most important aspect in reproducing music in the home . There is no way you will here the difference with a rack behind one speaker with dipoles . 
maplegrovemusic
I believe room acoustics is the most important aspect in reproducing music in the home. There is no way you will here the difference with a rack behind one speaker with dipoles.
Those two statements are in complete conflict with each other.
To not purchase dipole speakers unless you have a perfectly symmetrical back wall is the most preposterous thing i have heard . Explain the rational behind this ?
Although I'm new to Audiogon forums, I've been into high-end audio since the mid-80s.  Think Conrad Johnson PV-5 and Mark Levinson ML-2. I've learned that everything, EVERYTHING makes a difference. The only question is how significant, and how audible is it.
Listening to my dipole speakers . Funny thing just happened . My dog just walked behind one of them and the soundstage stayed consistent . No adverse affects were audible . Crazy !

Is he four or five feet tall? ;-)

She’s a Bullmastiff ;-)
I agree with prior post re trying to maintain symmetry by placing something acoustically equivalent behind the right speaker as well (perhaps even something on wheels, if can't locate there permanently).

I have ML Expression's (formerly had Summit's) in my asymmetric family room (with large open hallway on right side).  Using a combination of absorption and diffusion, via custom bookshelves behind the speakers, plus a bit more than the recommended "toe in," I've been able to tame the back wave so I still have a deep soundstage and centered image.  With a little creativity and experimentation, you should be able to make it work.
Would you please explain why you'd put absorption behind a dipole speaker, when part of the dipole concept includes reflection off the wall behind the speaker?
@cleeds the sound reflected off the wall behind the speaker is not a GOAL of dipoles it's the DOWNSIDE aka THE COST of dipoles. Try reading the setup tips page on Sound Lab's site for detailed explanation including the math. It boils down to minimizing what you hear from the late extraneous back wave of sound will give you the most satisfaction from dipoles.

The dynamic woofer behavior is another ball of wax with another pile of suggestions I'm sure. That's why I prefer full range electrostatics to hybrids. Cheers,
Spencer 
sbank
@cleeds the sound reflected off the wall behind the speaker is not a GOAL of dipoles it's the DOWNSIDE aka THE COST of dipoles. Try reading the setup tips page on Sound Lab's site for detailed explanation including the math
Oh no, I couldn't disagree more. If you're interested in reading, read the setup manual for Infinity IRS series. The reflection off the back wall from a dipole speaker is deliberate, by design; manufacturers could easily prevent it by not leaving the drivers open in the back. But they don't.

I have Martin Logan Aeon i towers 2.5' off my front wall with floor standing abfusors behind them.  The absorbers/diffusors made a positive difference when I added them.  I also had a vertical equipment rack near my left speaker at the same height as the electrostatic panel, and I was certain I was hearing the reflections off of it.  I bought a new equipment rack that was lower and wider so it fit between the speakers (with the TV now on top of it), and getting the rack and gear out of the vicinity of the mid/high frequency beam fixed the reflection issue.  

It is possible to hear differences in the music when you change the surroundings of these speakers.  You don't need to have them 5' out into the room, but I would try to give them space as your room allows, and I'd try to get your equipment out of the way, even from the rear wave, or try to do some symmetrical diffusing as previously suggested.
Thanks for all the feedback. I think, personally, I'll take rearward firing energy out of the equation and go with a conventional speaker design.

maplegrovemusic,

Same thing happened to me. I was doing a double blind listening test with a couple of friends comparing interconnects. My wife happened to step behind my left Aerius i speaker to switch on the little spot light on the floor and my buddy raised his hand thinking I changed the interconnect....Incredible...(OK, if you thought I was serious, I have a bridge to sell)..

Sorry, just could not resist.

kalali ,
You do not need to have bridges for sale , just fancy overpriced audiophile marketed  equipment . 
Before throwing in the towel on stats, you might consider Janszen hybrid electrostatic speakers, which can be placed closer to the wall because they have a closed cabinet with back wave absorption.

OP: "Thanks for all the feedback. I think, personally, I’ll take rearward firing energy out of the equation and go with a conventional speaker design."

Conventional speakers also have rearward firing energy as well as a lot more energy hitting the side walls, floor and ceiling.

OP: "I’ve learned that everything, EVERYTHING makes a difference. The only question is how significant, and how audible is it."

Unless you have a room that is particularly unsuited for electrostats, and you would have to try them to know for sure, electrostats should not be more of a problem than other speaker designs. As you know, all speakers come with their own issues.

The op was scared away from bad advice early in the forum post . Too bad . Hope he gets to hear some stats in his future .
I have an uneven front wall with my Magnepan 3.7i's.  The left speaker is 9' away from the wall and the right speaker is 7'.  I don't think there's a noticeable difference, but it could be because they're far enough away from the front wall already.  I was surprised that I could tell the difference in sound quality when the speakers were 7' and 5' away versus 9' and 7' though.  
@sleepysurf Good suggestion. 
@cleeds So Janzen closes their cabinets and Sound Lab recommends a "Dead End/Live End approach that absorbs the rear wave. Who recommends your preferred "Let the rear wave bounce approach" besides Bose? Cheers,
Spencer 
If you have one speakers wall 4' behind it and the other 15' behind it your going to have an issue . These guys were fretting over having a rack behind one speaker  and not the other . Ill take a stat 2' from a back wall over boxed speaker 2' away any day . If panel sound is your thing you will live with whatever compromises might arise in your room . I have since moved from the room my system shows here on agon and one speaker has a wall of diffusion and the other aims right into a floor to ceiling corner bass trap . Still i am getting optimal sound . 
If it were me, I'd find another place for the rack...think out of the box, it would be worth it.  I don't see you compromising the Ayre's excellences.
sbank
Who recommends your preferred "Let the rear wave bounce approach" besides Bose?
You’re obviously being facetious, because Bose doesn’t make a dipole. But, to answer your question:

Infinity (of yore)
Martin-Logan
Genesis
King Sound
Polk Audio
Kef
Quad.

Then, there are the manufacturers who try to imitate the dipole sound, such as those who make bipole speakers. You can look that up for yourself. There are also posters in this thread who concur that the rear wave is an inherent - and useful - part of dipole design.

Any dipole speaker manufacturer who wants to dampen or eliminate the rear wave can do so by using construction that will block the rear wave. Simple.
I should have also mentioned what is perhaps one of the grand-daddys of all dipole speakers ... Magnepan.

Do you use grand-daddy literally or figuratively, cleeds? Magnepan has probably done more to popularize planar speakers than any other company, but the original Magneplanar Tympani T-I was not introduced until 1971, long after the original Quad ESL in 1957.

The Quad has absorptive pads on it's rear, installed by Peter Walker to make it more room friendly for the relatively small lounges of British houses. Maggies benefit greatly from space behind them (the more the better), but can be placed quite close to side walls with no sonic penalty.

bdp24

Do you use grand-daddy literally or figuratively, cleeds? Magnepan has probably done more to popularize planar speakers than any other company, but the original Magneplanar Tympani T-I was not introduced until 1971, long after the original Quad ESL in 1957.

I meant it figuratively. I agree with you - Magnepan has surely promoted the dipole/planar speaker better than anyone else, but Quad was on the market long before them.

Per Martin Logan 2+ feet off front wall is acceptable. In my set up absorption on front wall flattened the sound stage. Diffusion however maintained sound stage depth but gave more solid imaging. Untreated the sound was very enveloping but seemed sort of disembodied. My room is only 12 x 15 so I can’t get too far off front wall. After a bit of trial and error I am pretty happy with 35". I built a pair of skyline diffusers 18" x36".
Box speakers near walls have their own problems. The MLs work pretty well in a small room because their directionality minimizes side wall and ceiling reflections. I would second the idea of balancing your front wall topography with some kind of diffusion.