[csero]

 It has been shown mathematically that two channels have the ability to carry enough information to produce a 180 degree hemispherical sound field...

Could we see that math???

[Aether Audio]

csero,

Aarrgghhh!  I should'a known someone would ask for that.  Well...I have the info, but it's buried somewhere in years of back-issues of the Audio Engineering Society Journals that I have - but God only knows where.  All I know is that I remeber reading the article.  It was part of a paper that was written regarding surround-sound research.  I think NASA or the AirForce had something to do with it, or it was being done for them.  If I remember correctly, they were working out algorithms to synthesize 3-D sound from the two-speaker headsets built into fighter pilot helmets, so they could "hear" which way enemy planes, missles, etc., were coming from.  Also, I think that research led to speaker systems that are being marketed by Bose et.al. to generate surround sound from one or two little speakers being built into TV's or set on the shelf next to a TV.

Although I don't have time to dig up the info, if you've ever heard one of these systems you have to figure it's possible.  I have a cheap little Sanyo stereo TV that has that built in.  Although the sound quality is crap, it is sort of cool.  On the right program material and sitting in the "sweat spot," I've heard stuff coming from behind my head.  Yeah, it's synthesized, but in the end it's still only two speakers.

Come to think of it, I also remember Mathew Polk doing a paper on his old designs based on his Inter-Aural Time Delay research.  I think that paper showed pretty much the same thing.  Remember Carver's preamp that included their "holographic processor?"  It was based on the same research and supposedly created the same effect as Polk's speakers, only electronically.

Anyway, none of this is much help...I know.  Sorry, but if you want to do a Google search or check out the AES, I'm certain it's out there.  Hopefully using some of the key words above will help.

Good luck,:D
-Bob

[tanchiro58]

I agree with Randy. The whole stereo system depends on all components including source (CD player, CD transport and DAC), preamp, amp, speakers and all interconnect and power cables. They have to be matched. Not only that but also depending on the individual music taste. But the most important thing is the design of each component is also depending on the characteristics of the tubes (I am talking about tube gear ONLY). What do I mean? Let's focus on a tube preamp or amp. If you know one special tube you choose you have to know how to build the output transformer for that special tube in order the tube has its full performance... Maybe I am going to far to details of DIY. But that is true for nowadays problems for music lovers and/or audiophiles, who keep looking for a good system for their taste and keep spending tons of money but have never found their satisfaction.

[Russell Dawkins]

For the record, as an "imaging freak" for the last 30+ years, here's how I set up a system for most effective imaging.

I am talking about optimizing the set up with what you have to work with, and I have heard good and bad results with all the usual variables - dipolar/bipolar/point sourcel/line array; tubes/solid state; live/dead rooms.

I won't go into great detail, but my approach involves checking progress with mono reproduction. If you don't have a mono button somewhere in the signal path, get a Y-cord. If you do have a mono button and it precedes the balance control (if you have one of those), a refinement is to face the speakers together and adjust balance for maximum cancellation with one speaker wired in reverse polarity. This adjusts for variations in gain characteristics and speaker sensitivities.

Now, rewire the speakers to correct polarity and start playing with configuration. Judge your results from the intended listening position, seated or squatting. What you want to hear is a very narrow mono image - the narrower the better. If you are lucky enough to get it right, the sensation is like hearing music through a vertical slit in a very high brick wall. Any flaws in room set up or speakers will result in lateral smearing, sometimes at one or two frequencies. Pink or white noise (mono or correlated) can be interesting in this context, in that all frequencies are represented and problems relating to imaging at some particular frequency are easily identified.

Anyway, that's it - just go for the narrowest mono image. The rest takes care of itself. I have never known this not to work.

[jon_010101]

I was listening to a xylophone once on a HT system and as the performer ran from one end to the other the imaging was good enough to to start at the right and move left, however a TV was in the way and while the sound remained, the image was lost while "in the TV". Another instance involved a coin rolling across the bar, falling to the floor, and rolling in a circle to a stop (had the speakers been mounted on the floor it couldn't have sounded like that).

Hey, sounds like you were listening to Gentle Giant's album Octopus.  One song has the coolest xylophone ever, followed by another song with a coin flip / fall / roll.  I could be wrong though  

[dado5]

As has been said here already, the most important factor is the recording.  If the data for a wide soundfield is not on the recording, it ain’t gonna come out the speakers.  

It is also important to note that detailed imaging well outside the edges of the speakres is not a natural effect of stereo recording.  It is rather a deliberate manipulation of the signal.  This is employed in many TV broadcasts in the form of signal phase and delay to get far right/left effects from the two speakers but it is rare in recorded music.  Bob pointed out the Carver and Polk approaches which used a delayed channel crossfeed  to create similar effects, but these did more the harm the stereo illusion than help (notice the products are not around anymore.). I owned a Carver pre that had his‘Sonic Holograpy’ circuit in it and it only worked well on a few records – the Beatle’s Sgt Pepper comes to mind - on most stuff it slightly broadened the soundstage but smeared the imaging. In short don’t expect to hear a guitar pop up on the left outside of the speaker.  

What you can hear from well recorded piece with good electronics and well placed speakers is an enveloping halo of sound. This soundfield will have detailed imaging in the plane of the speakers with a sense of in room presence that includes ambiance/venue space sound from outside the speaker boundaries. This is a good as it will get from two channels without signal manipulation (phase/crossfeed/DSP/room correction or whatever). Room treatment may enhance the effect (most notably in projecting the images forward of the speaker plane for a more 3D sensation.) and I would add that the Single Ended Triode/Single Driver thing is pretty amazing in this regard as well  but nothing truly ‘stereo’ is gonna move that guitarist to your left shoulder .

Thanks,
Rob

[pistolpete]

I have NEVER heard better imaging than [audio physic] speakers.  
DO NOT BUY until you hear these guys.  I promise goosebumps!
I have heard:
Virgo
Step
Spark
Tempo
All have first rate imaging.

[Hantra]

I totally agree that probably half of that comes from great room acoustics, which can be easily attained these days for not a terrible amount of money.  I have a few hundred bucks in tratements from Eighth Nerve, and my room measures as flat as any I've ever seen, and sounds amazing.  I have the new series of Eighth Nerve stuff on the way, and I am excited to hear the improvements they'll bring about.

I also agree with the guys who are talking ribbons or planars.  Most ribbons to my ears have a sort of unnatural ring to them.  The ones I love are Piega Limiteds.  They aren't dipolar, and don't ring.  They play to 60khz, and are supremely accurate, while maintaining a sense of emotion and never getting harsh.  Piega also has this amazing ability to match the bass to the fast ribbon drivers.  I don't know how they do it.  It's either some amazing mathematics, or just serendipity.  I don't really know, but I have yet to hear a speaker with bass that is perfectly, and seamlessly matched with a ribbon.  In fact, I heard a $15,000 speaker the other day that couldn't even manage a coherent sound between a woofer cabinet and a tweeter/mid cabinet.  

I'm rambling now, but I would encourage you to go out and listen to more speakers to try and get where you're going.  Give Quads a listen also.  To my ears, the Piegas do about 90% of what the Quads do right, with 0% of the drawbacks the Quads have.

Also, keep in mind that unless a speaker is perfectly time aligned in a room and setup correctly, it ain't gonna image very well at all.  

One more thing. . . Some speakers do a "you are there" experience, while others do a "they are here" experience.  It's important to know which you prefer when selecting the right speaker for you.

Hope this helps,

B

[_scotty_]

With my current system,whether I pack my bags or make up the spare bedroom depends on the recording. With luck you can have your cake and eat it too.
Scotty

[John Casler]

One more thing. . . Some speakers do a "you are there" experience, while others do a "they are here" experience. It's important to know which you prefer when selecting the right speaker for you.
...

This is a "VERY" interesting and important point.  And each experience is also VERY different.

"You are there":

The "You are there" experience takes your room and surroundings out of the sonic equation.  That is, for all intents and purposes when you close your eyes the sonic information, soundstage and imaging is as close to the real venue as possible.

This takes a very special room, room treatments, system and speakers to fully appreciate.  If you have "any" room related sound, the ability to perform this presentation is degraded.

Noise, distortion, and reflections must be minimized to the point that you can hear the ambiance of the specific venue.  If it is a "studio" recording if may sound a little flat, and each instrument and voice will have a clear and distinct texture according to the miking and the surrounding damping material of the booth or section that the instrument or vocalist is in.

Kinda like headphones on Steroids in 3-D.

"They are here":

The, "They are here" sonic is much different than the "You are there".

This Sonic incorporates the performance "with" your room  and its ambience.  This is ususally a very pleasant presentation, but not as realistic, in the actual recorded signal sense.

It doesn't offer the ability to hear as deeply into the original venue because the ambience of the two are combined, and the subtle ambiant cues are masked, or combined with another set from your room.  

Performers are rendered to sound more like they are "in your room" complete with part of your rooms sound.

Even Studio Recordings are nicely rendered with the natural ambience of your listening room.  Etched reality is blended with smoother images and an "airyness" to the soundstage.

Audiophiles with Dipoles or "omnidirectional" (360 degree) speakers seem to enjoy this type of presentation, since that speaker type by its nature interacts with the room to create its "sound".  

Also those who like "larger than life" and huge soundfeilds or soundstages like this alternative.

[djbnh]

Bob pointed out the Carver and Polk approaches which used a delayed channel crossfeed to create similar effects, but these did more the harm the stereo illusion than help (notice the products are not around anymore.).

Re: Polk. I won't say I agree or disagree. However, I point out that there's quite a few SDA owners who would not hold the same opinion as you. If you are interested, please go to Club Polk, Vintage Speakers and bring your point of view with you. FYI - you may wish to reconsider the veracity of your statement that Polk speakers use "a delayed channel crossfeed".

[JoshK]

I am quite a bit surprised that all this talk about 3D holographic sound and no buddy mentioned the single most important factor IMO, diffraction control.  I think that there is quite a bit of evidence of this in literature and studies.  

You want your speakers to dissapear you absolutely need to control baffle related diffraction, especially in the presence region (1K-3K).  No wimpy 3/4" roundover is going to do it, you either need a waveguide like SP Tech does or a 1.5" or larger roundover.  Why audiophiles don't require it for there speakers is beyond me.  

Some of the best DIY'ers and experienced speaker builders I've read have done experiments to this affect and proven it to themselves at least that this most definitely matters to allow for your speakers to dissapear.  Of course things like even and consistent off axis response, particularly through the xo region is necessary as well, even more important that on axis response.

[dado5]

Thanks for the response djbnh.

I like you signature line BTW - Soli Deo Gloria!


Polk and Carver's technology were indeed centered on delayed crossfeed.  All such systems are because the operating principle is cancellation of the delayed sound from one channel being received at the opposite ear (interaural crosstalk to be pedantic).  Carver did it electrically and Polk used an electro-acoustic effect.  The SDA system used extra drivers that received an inverted signal from the opposite channel.  From what I remember of the white paper, the Polk system delay was accomplished via the driver placement (I don’t think there was an electrical delay involved). The antiphase  drivers were spaced to the outside of the direct drivers so the wave front arrived at the ear coincident to the unwanted crosstalk from the opposite speaker, thus achieving cancellation.

I had only heard the Polk system in dealers but my exposure  was pretty wide as they were a big demo item back in those days. What I heard, depending on the recording, was  a tendency to either a ‘hole in the middle’ affect with the sound centered around the two speakers or a very strong center with other instruments coming from outside the left and right speakers. It was more similar to headphone listening than anything else, which makes perfect sense given the design goal of the system.

No doubt this approach has lots of fans, but I never got into it aside from the neat effects it produced on Sgt. Peppers.


JoshK:

Can you go into more detail on the effects of  difraction or point us to some web info?

Thanks,
Rob

[_scotty_]

Here is a link to one of the better articles on diffraction:
http://stereophile.com/reference/704cutting/
Scotty

[Hantra]

Okay, the diffraction article is good, and it's a decent explanation.  But diffraction is merely one factor.  A truly great speaker gets much more right than just diffraction.  

I've heard speakers that apply this theory, and I wasn't all that impressed.  In fact, if diffraction is the most important thing, then all B&W's from 804's up would be the best speakers on the planet.  And while they are great, they're far from perfect.

I suppose my only point here is that it requires quite a bit of technology, expertise, and perhaps even more artistry to create a truly great speaker.

[JoshK]

Absolutely true, Hantra....I was assuming we were already talking about an excellent design and that diffraction was the last part in making it dissapear.  All too often the "low diffraction" type of speakers, #1 aren't really low diffraction and #2 they do a bunch of other things wrong.

I have also heard the opposing side of things were they feel diffraction is severely outweighed by the comb filtering of stereo reproduction and to me this was the most convincing rebutal.

[transam]

Let me throw in my two cents.Speakers are the most important thing to get.Then would be room treatments , gear.In my martinlogan ascent setup everything images including cable tv,but nothing sounds as good as sacd/cd.On some recordings i can here sounds behind me and middle of room left and right.It's pretty bad ass.

[csero]

You can create realistic 3D sound if you can:

- deliver the same sound pressure at each ear independently as it would be at the real event
- minimize HF directional error
- ensure the consistency of the aural clues in case of head movements

Knowing this the question is not HOW CAN you do it with a stereo setup, but HWY COULD you do it.