Hey guys...we need a little rallying here... - Page 232

The significance of a dipole surround loudspeaker, relative to a bi-pole or monopole, is that the dipole is unique in providing a wide-band null that can be oriented towards the listening area, such that any direct sound from the surround is minimized, providing more even envelopment and a delayed arrival of the surround signals, emulating the longer path reflections of a larger venue. It also simulates the envelopment of a large number of point sources, which can be achieved by using more than significantly more than two monopole or bi-pole surround loudspeakers. A dipole surround will tend to provide the largest apparent surround sound source, a greater number of perceived directional angles of arrival, and largest virtual environment size from a single pair of surrounds.
This is in trade for a somewhat reduced image specificity, and one can decide if that is important in the rear hemisphere. At 90-degrees to the side of a listener, perceptual angular accuracy is minimal, regardless of source type.

I hope this is helpful.

All the best,

- James

It is helpful James. As are all your posts. Wish you wouldn't lurk so much and would post your wisdom more

Sounds really nice when put that way. But here's another spin on it. The lister sits in a giant suck out only to hear reflected sounds to create an artificial spaciousness over and above the recorded spaciousness. The speaker suffers from reduced sensitivity and design complexity.

I've really only dusted off the surface of the concept, so maybe I'm out to lunch. But couldn't NicksHitachi take a two-way design with wide dispersion, build two angeld 45 degress. Wire one out of phase. And bam, he's got a dipole surround (not exactly a true dipole like a Nao Note or similar, but would have the dipole null facing out towards the listeners.)

True, but only if it's CD, meaning level drops off with angle.

Except...the "dipole" speakers marketed as surrounds as a rule aren't actual dipoles. Or particularly close to dipole, for that matter.

Not sure how a "dipole" or even an actual dipole (say, a 75" BG planar perpendicular to the wall) would be superior to a more omnidirectional speaker in that regard, except perhaps due to mild precedence effect.

Why controlled directivity if you want an ambient sound? Why not an omni directivity? For surrounds, I say let them reflect and illuminate the room. As long as the polar pattern is uniform. And I think that's what you mean. Surrounds should be uniform off axis.

That's why I have mine aimed at the ceiling.

Thanks for the kind words.

There are two issues here to address:

Ultimately, you are correct about the artificial spaciousness of a dipole.

When I was a younger man, I was at a Frank Zappa concert and someone yelled at the Police guard that they were Gestapo sheep, all wearing the same uniform. Zappa looked out at the crowd of us quasi-hippies and said, “Don’t fool yourselves, you are all wearing uniforms”.

Analogously, I would have to say, we are all creating artificial spaciousness, above or below that of the original first venue sound field, both quantitatively and qualitatively.

We do not yet have a recording capture and playback standard that works, so we each make the decision as to how best to make our systems achieve a presentation that is as uncolored and neutral as possible. And then, in the realization that it still cannot fool a 5-year old into believing they are listening to a live event, we must determine how much, and what type of enhancement we wish to add to create a sonic event that at least somewhat allows us to best experience a suspension of disbelief.
To paraphrase Frank, we need to not fool ourselves, in that we are all incorporating complimentary distortions of the original signal to attempt a compelling facsimile of the live event in our room.” Often those wonderful audio components that we find so striking, are not necessarily reaching into the program source and drawing out reality, but instead are distorting the signal in a manner that better fools us into believing.

Dipole surrounds, provide that same enhancement, but does so in a such a way that at least the ear/brain is not drawn to the sound source in an manner that points to a sound source. Again, it is the simplest source that can achieve what it does. In fact, one can even use a single dipole, centered directly behind the listener and achieve envelopment and/or ambience that is more convincing than a use of one or two monopoles.

I did a lot of work with dipoles in the 1970’s and 80’s and patented dipole configurations for use in surround sound, and licensed it to LucasFilm/THX.
You were asking why they were ever created in the first place. They were originally developed to use with delayed signal surround systems in the early ambience and 4-channel days, but were specifically chosen for the THX specified systems to maximize envelopment and scale in an attempt to recreate the surround sound systems in the theaters that use many side and rear loudspeaker sources to create the surround sound effects. While my original reference systems for domestic use were based on using 6 to 8 surround speakers in a 2-2-2 or 4-2-4 LS-R-RS format, and this is still the most impressive for home use, it was not acceptable for most domestic environments. So, the dipole surround was applied to the home theater specification of the time as a multi-speaker emulator, with the preferred addition of a decorrelation processing function. This provided the most faithful in-home replication of the sound in the dubbing stages that were used for mixing movie soundtracks.

Dipoles are often criticized because they are not configured properly to reach their full potential… as it is with most things audio.

Which leads to your second question, which if I understand correctly, asks about the use of two wide dispersion speakers, each angled at 45-degrees, and operated out-of-phase as a dipole system. While this approach can realize a dipole surround effect, a problem exists with achieving adequate low frequency extension. If the device is too small, and/or the opposite polarity drivers positioned too close together, without an intervening baffle, the high-pass characteristic of the dipole will start at too high of a frequency for the system to maintain reference level response in the lower midrange.

Bill Waslo’s mention of two constant directivity 90-degree waveguides, angled at 45-degrees to each other, as I believe you are also suggesting, can work very well, in-phase, as a bi-pole, as a natural null is created orthogonal to the mounting wall without requiring the out-of-phase cancellation of a dipole… but, that is only maintained down to the lowest frequency of waveguide pattern control, which is too high of a frequency unless very large waveguides are used.

There are a couple of other configurations that achieve dipole cancellation but for a single source device per room side, the other devices that are commonly known that work reasonably well are a floor to ceiling line source or a CBT based system, but these still should be used in multiples of at least two per wall if envelopment and lack of source detection are desired (There strength is that they are excellent at maintaining even SPL level across the listening area, left to right). Combining a line source and dipole can make for a best of both worlds device.

I apologize if I rambled more than what was requested with the question, but these few paragraphs just scratch the surface of the topic which has many factors to consider to approach the ideal result.

Cheers,

- James

Enlightening rambling IMHO.

Good food for thought, Thanks. I gotta think about this a little, because I still feel there are to many problems with it. Specifically combing. Unless using a true dipole.

"a problem exists with achieving adequate low frequency extension"

Oh of course. Didn't consider the bass cancellation.

One consideration I had when going all monopole was support for multi-channel music mixes (not there are a lot of good ones, but one can always dream), in addition to HT surround.

I agree that most that are marketed are not true dipoles.
Poor execution is part of the problem that causes dipoles to get a bad rap. As with most systems that have a greater degree of complexity and a greater degree of design freedom (such as a bass reflex compared to an acoustic suspension woofer), a dipole requires more careful optimization than a monopole to reach its full potential. I would rather have a properly designed monopole than a poorly executed dipole. But, if one is willing to go to the extra effort to get it right…


Actually, not so much precedence effect but rather an example of a later arriving, greater amplitude signal, overriding the psychoacoustic precedence timing, and with proper null, defining the first perceived source origination being that from shortest path reflection(s).
Since you mentioned the BG device, you may find it interesting that some of the first and best dipole surrounds for home theater were created from the first planar magnetic line sources developed myself and David Graebener (the “G” in BG) in the early 1980’s. These were the reference model for the variety of later dipoles that were marketed (some good, some not so much).
As, you suggest, a more full range dipole, such as an elongated planar magnetic line source, properly baffled makes for a much more effective expression of a dipole surround loudspeaker.

- James

Up firing would be an issue as I wouldn't want one of my pets landing on those pretty cones.

I doubt that it needs to be said in a group as directivity savvy as this group that works with CD waveguides, but unless a loudspeaker is a high directivity design or one that has wide-band constant directivity such that off-axis output is substantially reduced over thee bandwidth of use, then it is going to still be perceived as if it is aimed at the listener, with a tendency for a somewhat unbalanced response at the listening position.

"Pointing" loudspeakers that don't have purposeful directivity for a particular orientation tends to be a recipe for coloration tonally, even if one enjoys the spatial effect.

Also, since the surround sources are usually best used above the vertical centerline of room, it can also produce combing in the response as the ceiling reflection interacts with the direct sound, similar to floor bounce reflections from the main left/right and center loudspeakers. Not quite as bad, since the side arrivals are somewhat de-correlated due to cross coupling with delayed arrivals to opposite ears.

it is good to define clear tonal and spatial in room target functions and avoid, as much as possible, not having to sacrifice timbre or directional factors or trade off one for the other.

I find that a lot of systems that carefully maintain constant directivity and smooth power response from the direct frontal channels can have an excellent lifelike, low coloration direct and room response, only to be substantially compromised tonally by adding surround channels that don't maintain the same power response integrity and timbre matching.


Cheers,

- James

Very good discussion thank you guys.

I see a lot if good points.

For small rooms like mine i believe there is a niche for a non-controlled directivity design. One which is high sensitivity and high quality to match the SEOS designs. I dont see ruler flat response and controlled directiviity as requirements for surrounds. Just my opinion.

If we see this as fruitful ambition ill help as i can to get this done.

James,

A common argument for monopole surrounds is that monopoles are used for mixing the soundtracks in the first place and it should be upto sound engineers to decide when and to what extend make the sound defused or directional. Using di-, omni-, etc., speakers for playback will by definition deviate from the intended effect.

What's your take?

This is extremely interesting stuff. Maybe we could start a new thread to see if we can come up with some practical solutions to this.

I'm thinking maybe cardioid resistive enclosures would solve the lower frequency directivity issues. If each bipole can maintain tight directivity down Schroeder wouldn't this solve the problem?

I think the problem with monopole surrounds is having them near a wall or ceiling. That gives you near reflections and at least one deep and wide suckout (I've tried with an omni). In most rooms, mine included, something 180degree or less would work better.

zheka;;

To address this subject properly is beyond the scope of a couple of postings here, but I will start by mentioning a few points.

One of the significant advantages to Lucasfilm/THX standardized recording methods was that the dubbing stage used for mixing 5.1 (or more channels) was well defined and set up in a manner that could be substantially duplicated in a domestic environment. They used a diffuse surround sound delivery.

In most quality surround sound studios, if monopole surrounds are used, most often they use a multiplicity of monopole surrounds to create a diffuse field with directional cues that at best create directive elements to a wide apace in one of three 60 degree surface angles.

To mix to a simple two-monopole speaker surround system without false over-localization in the rear sound field is very difficult.

The goals of proper movie or music recording, is to never have a sound source that draws the attention away from the frontal presentation of the movie screen or orchestra stage.

That said, there are many sound engineers that can't help themselves and must sensationalize with specific music instrumentation that comes from behind, but I assume that is not what we are aiming for here in high quality home reproduction systems.

But, maybe I'm wrong... I don't know the desires of this group. I would like to hear more about what the gang here would like to achieve. Is most of the use for music or home theater? Combined systems or separate for music and home theater?

- James

That's the most common/traditional approach, and one that would best emulate the experience of listening to a band at a concert, etc. - but not the only/"right" way - I was very impressed by the experience of the "stage mixes" that AIX records offers (filecat13 was kind enough to hook several of us up for a tour/demo at Mark's studio last year):

http://www.aixrecords.com/techtalk/5_1_stage_mix.html

I prefer that feeling of being "in" the music, vs. listening to a performance in front of me - sadly, not many artists are available with this kind of mix, and even fewer mainstream.

 

I think most people here are using their systems for movies with the occasional concert/music. My brain hurts trying to look for the perfect surround that fits my needs. High sensitivity, smallish, and the big one...non-directional. The one speaker that seems to fit is the 1 pi in a sealed enclosure.

Same here.
I ended up buying these. Haven't installed them yet.
http://www.parts-express.com/pe/showdetl.cfm?partnumber=303-446

I've seen "horns" that they use for line arrays that basically have no external flare at all. I think they just have a CD mounting flange, then inner phase correction channels (or whatever they're called), and then a straight shot out the front of the baffle. Would those help? They also make some that you can mount 2 - 3 compression drivers in the same horn. Would wiring 2-3 small CD's differently in the same horn do anything? I don't know much of anything about surround speakers.

They're diffraction horns. They achieve their directivity via, as the name implies, diffraction. That makes them inherently better than horns with a wide mouth, which basically force waves to do something they don't want to do. But the requirement that they be vertical doesn't always mesh well with the rest of the speaker. Klipsch used EV 8HD and T35 diffraction horns, and he placed them horizontally. He knew it was the wrong orientation, but never really said why he used them instead of horns intended for horizontal placement. My guess is that it was purely related to his having a relationship with EV that wasn't competitive.

Except isn't the 1 pi an 8" with flush dome? I doubt that would have a uniform polar response, which is important for surrounds.

For high sens and that kind of package, ill be using the sb29 neo crossed to a 5 or 6" at 1500 to 1800hz. But I don't have a large listening distance. That'll give a uniform polar response and wide vertical lobe. If I have to, I'll make it a compact 3-way with an 8" woofer.

So important it needs to be repeated.

How about a shallow cab with tapered sides against the wall,or an in wall cab to eliminate the issues with the nearby wall. And keep it a healthy distance from the ceiling. Might do ok.

Thanks for the information Bill. What if the 2 CD's were wired out of phase? Or on a 3 driver model, what if the 2 outer ones were wired differently than the middle one? Just curious.

I appreciate the response, James.

So the basic flaw in the "mixing with monopoles" argument is that it's often not true, at least when it comes to movie soundtracks. Good to know.

I believe that describes my experience with Mirage OMD-5 omni cans. While the sound was more diffused they just could not keep up with the fronts at all.
Can you name a few commercial surround loudspeakers that may be adequate for performance HT?

You mentioned that using multiple monopole surrounds may lead to good results too. What do you think about surround formats such as DTS ES, Dolby EX that matrix surround signals from 5.1 mixes to the rear channels?

thank you

The reason for using multiple drivers on those is two-fold, for power handling and to minimize the pathway length differentials of the wave down the center of the horn versus the top and bottom. That's the reason for the use of multiple channels as well, as seen in this Carvin:
http://www.carvinguitars.com/trx3210/

PureBASS, am I correct if I'm guessing your name is James Croft?

Got my shipping notification for my TD12M Phase Plugs. Yay!!! Should be here in 4 days. Erich, I don't know if you've had time for those baffles and boxes, but if so, let me know.