Dipole speakers, subwoofers and that rear wall

If you are using a diffusor you must understand that a true diffusor is based on mathematical properties and not random variations in a surface. Not saying that these arent true diffusors but you have to be careful. My diffusors were made by RPG and came from a speaker designer/manufacturer who no longer needed them. 

I sort-of have a dipole subs - SVS PC4000s - ports at the top, downfiring at the bottom. ;) - 

I found these diffuser panels: they look fairly nice too 

Which ones are the best for the situation (quads in a corner, subs behind them.. 

I can't let a discussion of dipole loudspeakers and subwoofers go without mentioning one combination of the two that is very unique: the dipole speaker of your choice mated with an OB/dipole sub.

Brian Ding of Rythmik Audio and Danny Richie of GR Research put their big brains together and created the world's only servo-feedback (all Rythmik subs are servos) OB/dipole subwoofer. Details on both company's website. THE sub for dipoles. 

I designed my dual 21" woofer OB to function as a rear-loaded horn by incorporating the boundary reinforcement generated by near-wall placement works wonderfully.

Wow...at least a couple people got it right. More than usual.

Why is dampen not better? To retain audio power (SPL)?

I wouldnt dampen I would diffuse. You should be O.K. if you are at least 3 feet from the diffusors.

This is awesome discussion, thank you all. Just a few responses and keep it going ;). One thing I'll say about my Quad 2912's is that I have had many audiophile listening sessions with people bringing their own gear - sometimes outpricing them by miles, and in blind(ish) listening tests, people always positively picked out the quads. 

That doesn't *necessarily* mean they are better in the eyes of an engineer with a microphone and an analysis program (REW?) but somehow the result apparently is pleasing. I'd note though that my receiver has a bunch of 'fake surround' options that sometimes accidentally get turned on, and funnily enough they sound great, and if I then switch back to direct mode, it feels 'deflated'.. for a minute... and then I appreciate the non-warbly non-surroundy perfect stereo image of quads. Perhaps the same applies here. Perhaps the stereo image effects that dipoles excel at outweigh the downsides of the rear reflect?

My context is that I am building my own livingroom-and-home-cinema. Completely from scratch (newbuild house). Due to wife-acceptance-parameters I will likely have to keep my quads fairly close to the rear wall (ignoring toe-in, about a meter (3 ft)). Behind them I will put my SVS PC4000s (I have 2). Ha, I slightly worry that the soundwaves from subwoofers will hurt the mylar of the speakers.

Anyway,  the weirdness for me is that if e.g. we have a single kick drum shot. Bang. If we have 10ms delay before the reflection comes through, does that then sound 'babang'? Is 'bbang' not preferable'? Either way most people seem to agree I should probably put damping material behind my speaker so I'll do that. 

The rear wave is not what these speakers are all about it is just, with most designs, a necessary evil. What you should try to do is minimize the downside to dipoles and then attempt to make them as accurate as possible. Listen to Duke's advice from Audiokinesis. Other than the obvious limitations of my Quads the only downside to this speaker is the rear wave and it must be dealt with. 

Oh, you mean "cabinet." That’s what most people call the box that holds speaker drivers.

What I mean is the mids and highs are in separate enclosures in the front and rear. They have NO common space between front and back mids and or highs. Usually about 18-22" apart (front to rear). Front baffle and Rear baffle enclosures are within the CABINET housing. They fire from the back of the speaker and hit the front wall FIRST. They don’t require such a large, long space to produce the same airy affect but they are deadly accurate also..

Small planars enclosed with NO open rear pole from the front driver. Way better design.. GR tried the same thing.. I had both of his Neo 10 x 2 and X 4. Like I said great sound affects, but accurate, NOT even close. His NX (?) different story.

Danny was also the fixer on the 123s too. Kinda.. LOL. They were just BAD. You needed a stadium size room to start with. The sweet spot was as wide as a sofa and it wasn’t so sweet. :-) There were several pairs around here 15-20 years ago.

GRs OB servo is a VERY nice system. I use it with Rythmiks sealed systems. They aren't cheap to finish out either.. Paint is through the roof.. 1K to 2K in one year for auto finish. 100% mark up.

For clarity, do you mean the front wall???  

Think of it like this.  When you go to a performance, are the performers in front of you or in back?

Dipoles are unique and enjoyable speakers.  As noted above, embrace and don't destroy the rear wave.  Use diffraction, NOT absorptive surfaces on the front wall.  Why would you want to defeat what this design type is all about?  If you can't pull them well off the front wall you will miss out on what these speakers can do.

For me, in the final analysis, dipoles are fun but not always the most accurate.  But in the right room with the right music, well you may be a very happy camper indeed.

What is a "tuned chamber?" I've never heard of this room treatment.

Instead of dipole, use both front and rear baffles and both are enclosed within the cabinet design. RM50 VMPS. There are a few more now. The old QLS Infinity.  NOT the RS OB design. RS1 & Bs and the 2 and 2Bs or the IRS series.

A boxes (or cabinet) with TWO active baffles, front and rear.

Tune the room?

Read my Handle.. Helmholtz. The only way to properly tune a room.. 

There is a guy that post here that uses the term "Embedding" he has 3 major areas. HE is very close on his design.. A little muddled in his room, BUT he did it by reading and experimenting. A brave endeavor by my standards. :-)

Helmholtz, I use adjustable slot resonators for above 120hz and adjustable tube traps for 120hz and below. All designed by SB/SAT. Oldhvymec's design, it works VERY well. I've used them for over 10 years. He's been at it for over 45 years. 

Curtains, Resonators and Tube traps. OHM bass system is the bomb. Ask him. He always helped me. I have one of his air ride decoupling systems from way back.

The ear does not perceive comb filter effects from reflections the same way a microphone registers them, so in general reflections are far more benign than they look "on paper". But if reflections arrive too early, they still can be detrimental to clarity. According to acoustic and psychoacoustic researcher David Griesinger, ten milliseconds of essentially reflection-free time is sufficient.

Sound travels approximately one foot per millisecond, so the implication of Griesnger’s finding is that ideally we’d want to position dipole speakers about five feet out from the front wall, which would result in a backwave reflection path length of ten feet, and a delay of about ten milliseconds.

In my experience, if dipoles (or bipoles) are placed less than 3 feet from the wall behind them, aggressively treating the backwave is usually a good idea. This can be absorption or diffusion or re-directing the reflection away from the listening area.

At distances between 3 and 5 feet it’s more of a judgment call as to whether or not you need to treat the backwave. Imo in general re-directing the reflection and/or diffusion are preferable to absorption.

Duke

dipole dealer, bipole manufacturer

helmholtzsoul

check out the room treatment page on soundlab's website for dipole specific recommendations (live end / dead end). Cheers,

Spencer

I "Embrace it" in a tuned chamber vs trying to tune the WHOLE room to the open driver. It can sound wonderful, but NEVER accurate. I've had to Endure dipoles more than Embrace them.. I had IRS Betas for 20 years. Wonderful speakers for the money. I did everything to those speakers.. Including "Embrace", I even divorced them a few times too. 20 year love hate relationship. :-). I really liked the servo bass columns. My first real DBA (4 servo columns). 1980-2000.

onhwy61

The rear wave is not the enemy. Embrace it!

It’s a timing issue, the front wave vs the back. The front wave hits the seated position, when the back wave is hitting the front wall. No matter where you put the front baffle, the rear of baffle has to travel further. Longer rooms help. Our user group went through this with 123s, 20 years ago. (GRs adopted nightmare). We or he could NEVER fix the problem. I must admit we all agreed they look awesome and have great sound effects, but most simple stand mounts speakers will whip the pants off dipoles. The only place they fall short is "SOUND EFFECTS" if that is your thing. I like a rear firing separate driver (s) for the back of the main cabinets. We ALL use SB/SAT design.

Subs are simple. Decouple the subs and raise them UP. Set them on tunable bass traps or between them, OFF the ground.. It’s like magic. Vs works very well in leu of conventional DBAs. The V baffle is at 30 degrees, the flat rear is a passive radiator. There are THREE directions the sound is coming from with a single cabinet. Two units placed on either side of the seated position is a full blown DBA less 2+ extra cabinets. It’s all the rage with US poor boys.. Again SB/SAT design.

I can imagine perfecting positioning for one frequency and its modes, but not for 20-20,000 hz full spectrum.

Try imagining more like 20 to 200 Hz (or 500Hz).
Or is the midrange a dipole too?

The rear wave does have further to go, so it will loose from R*2, and diffuse treatments are good for high freqs.

Sound travels at approximately one foot per millisecond. For two sounds to appear unrelated, they must be separated in time a minimum of 10 milliseconds (it’s a function of how our brain perceives and processes sound). For that reason it is recommended dipole planar loudspeakers be positioned a minimum of 5’ from the wall behind them. Why? The sound emanating from the rear of the planar travels the 5’ distance to the wall, is reflected off the wall and travels the 5’ back to the rear of the planar, 10 milliseconds after the same sound left the front of the planar. The rear wave therefore sounds like an event separate from the front wave; if the time difference is less than 10ms, the rear wave results in a smearing of the front wave.

But there’s more to the story: When the rear wave arrives back at the planar, if that wave and the front wave are out of phase with each other at any given frequency, the combination of the two may create a hole in the frequency response of the loudspeaker. Or they may combine to create a peak in response. We of course want neither of those to happen.

The way to prevent the rear wave from creating the above scenario---known as comb filtering---is to either absorb or diffuse the rear wave. Absorption needs no explanation, but it needs to be said that it may cause the sound heard in the room to be too "dead", lacking spaciousness, one reason for choosing a planar loudspeaker after all. A better tactic is to diffuse the rear wave; the random scattering of the rear wave prevents it from returning to the planar out of phase with the front wave, and keeps the sound produced in the room from becoming "dead" or lifeless.

@audition__audio - Ha, my challenge is that I’m fine with my quads stereo for music etc, no need for subwoofing - the situation that I’m thinking of is "loud" - movies at cinematic levls. 2912’s don’t go loud under say 100Hz, so I tend to cross over at that level.

Ah, compromises, compromises.

@onhwy61 - Ha, can you and audition_audio fight it out and tell me the conclusion? ;)

At the end of the day I’ll probably just *try* it, but I’m not even sure what to listen for..

I have my apogee duetta 2's away from the wall 7' I believe even further from the wall would be better if possible.

The rear wave is not the enemy.  Embrace it!  Pull the loudspeaker as far out into the listening space as practical and revel in the spaciousness.  A little diffusion could be helpful.  IMO, dipole and bipole loudspeakers require larger rooms to work their best.

This is the main problem with dipoles. My suggestion is do everything possible to cancel or diffuse that rear wave. Bring the speakers out into the room as much as possible and then put something behind the speakers to deal with the rear wave. The rear wave is the problem and you cant possibly bring the entire bandwidth of reflected sound into proper phase. 

You dont want your speaker doing anything other than reproducing what it is fed as accurately as possible. So the shape of an instrument should nothing to do with the shape of the transducer reproducing it. This is why I always get irritated when speaker manufacturers talk about making their cabinets out of the same material as instruments.

Dont worry about subwoofers and damage. Just be sure to cross your subwoofers over at the lowest frequency possible. Probably around 40 to 55 hz.