Fixing the Stereo Phantom Center

Works best that way, doesn’t it?
Doesn't it ? !!
I thought having just the exact same center-main working from 100Hz was good...it was. Thought that's all it would take.
Never expected how much having the same sub used L&R, under center too, would matter. It's crazy really.
All I know is Wow.

btw, the best matrix formula for I've found for LCR so far, has been what is called energy preservation.
Where the weighting to the sides vs center are trig based, not linear. As is the subtraction, L-R to give matrix left, and R-L to give matrix right.
Using various angles for for the cosine/sine, it lets how much is untouched stereo and how much is pulled to center.
I love it. But like said, best matrix is track by track/album. Although that said, some degree of matrix almost ways helps.
 
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Well good old Dolby Pro Logic that so many people love to hate used something like that, it pulled some center out of the sides. It was meant to give a wide image in a small space. Cinema doesn't need it, as the room and stereo base are both wide. Remember, in the beginning L-C-R-S where derived from two tracks. It was usually mixed 4 channel, but was stereo and mono compatible. You can certainly change to sound depending on the matrix. A subject I'd love to know more about.
 
I loved pro logic.
Best surround sound I've ever heard.
Un-localizable.

It was a Mcintosh preamp (not cheap), maybe 1992 - 1993 ?

Dipole rears 6' off the floor, maybe 6' from back wall (with the hf rolled off) really tricked you to believing you are in the scene.
Smooth, immersive rear sound.

If the scene was underwater, you really felt like you were underwater.
And surround should be subtle, as in you don't really know it is doing anything unless you turn the surrounds off.
That is the point of it (to me), unless a surprise sound from behind you.

But people/industry wanted stereo surrounds and 20-20khz all channels.

Now we have a mono rear channel.
I think there is even rear dipole channels nowadays.

To be fair, prologic cannot track front left to back right.

Some have said for music that a mono center (with stereo left and right) works well for music.
I've been curious what that sounds like.
 
Well good old Dolby Pro Logic that so many people love to hate used something like that, it pulled some center out of the sides. It was meant to give a wide image in a small space. Cinema doesn't need it, as the room and stereo base are both wide. Remember, in the beginning L-C-R-S where derived from two tracks. It was usually mixed 4 channel, but was stereo and mono compatible. You can certainly change to sound depending on the matrix. A subject I'd love to know more about.
I'd love to know more about it too.

Sometime I think plain stereo has done more to harm/retard the progress of audio that any single phenom, because it's deemed an acceptable compromise to both single speaker and multi-channel.
Single speaker rocks and is mostly about measurements/science imho. Multi-channel also seems to be more about measurements/science.
Both single speaker and multichannel R&D are led by objective prosound engineering ,....... theatre, live venues, etc
And both single speakers and multi-channel sound are typically designed for more than one person listening.
Whereas stereo is designed for one listener, in home, and often goes so crazily subjective and belief based..

Oh well, small rant over, sorry.
 
Yeah mono or three speakers would be technically mucho better.

I think there is something nice with the two channel stereo comb filter effect though, which makes this kind of magical feel to the sound. Because the middle is kind of bit veiled it leaves me to desire more, get into the sound and begging for focus or something. Makes the sound be there in front but kind of little bit out of reach, like chasing something, end of the rainbow. Like waiting for Christmas (as child) which then never comes and its always this excitement going on :D so, I'm not too troubled by it, more like trying to embrace it.

Most logical way to "fix it" would be by adding third speaker I think. I haven't tried the shuffling yet, perhaps its as good? I was quite happy with single speaker mono as well so that would be the easiest fix.

ps. its quite easy to hear with mono white noise fed to both speakers, strong phantom center forms. Then rotate head to one side and at some point the missing sound/clarity just appears, or comb filter shifts in frequency or something, very easy to hear. Quite interestingly, when rotating head to perhaps 60 degrees it feels the sound is most present and past that it goes duller again. While the effect could be from anything in my setup I think its the one, head related comb filter.

Btw. tried moving and delaying one channel, seemed to do nothing, not enough reflections I think. At least the head rotating trick did have similar effect to sound.
 
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Yeah mono or three speakers would be technically mucho better.

I think there is something nice with the two channel stereo comb filter effect though, which makes this kind of magical feel to the sound. Because the middle is kind of bit veiled it leaves me to desire more, get into the sound and begging for focus or something. Makes the sound be there in front but kind of little bit out of reach, like chasing something, end of the rainbow. Like waiting for Christmas (as child) which then never comes and its always this excitement going on :D so, I'm not too troubled by it, more like trying to embrace it.

Most logical way to "fix it" would be by adding third speaker I think. I haven't tried the shuffling yet, perhaps its as good? I was quite happy with single speaker mono as well so that would be the easiest fix.

ps. its quite easy to hear with mono white noise fed to both speakers, strong phantom center forms. Then rotate head to one side and at some point the missing sound/clarity just appears, or comb filter shifts in frequency or something, very easy to hear. Quite interestingly, when rotating head to perhaps 60 degrees it feels the sound is most present and past that it goes duller again. While the effect could be from anything in my setup I think its the one, head related comb filter.

Btw. tried moving and delaying one channel, seemed to do nothing, not enough reflections I think. At least the head rotating trick did have similar effect to sound.

Don't try to fix it if you have no problem ;).

Yes, 3 channels would have been better from the start, Mono wouldn't work for me (anymore) as a final solution, as I love what can be done with imaging as long as tonality is kept right too. But the soundtrack of my life is captured in the Stereo format. That's why I try hard to get the most out of it, for fun and learning. I was shocked at what I could achieve in Car audio as I had never really heard Stereo done right. Don't get me wrong, I had Stereo setups in my home, but never tried to chase getting more out of it. After hearing what was possible I was hooked and just needed to get something better in the living room.

Personally, I'd rate tonality higher than imaging. But when one gets both right at the same time it is starting to be way more fun. There's more of course, but tonality kind of is on top of my list. Imaging would be number 3 or 4? Still I want it all at once. :D
 
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Does Polk's SDA add to the combing or make it better? If you physically cancel the wave arriving at the opposite ear, then perhaps the head turn effect isnt as abrupt.
Well thats interesting system, see for example SDA1 manual which explains how it works https://polksda.com/manuals.shtml

Anyone know how its hooked up inside? the explanation is bit sketchy, how come sound reaches both ears but dimebsional sound doesn't?:D Drivers are probably head apart, perhaps the dimensional drivers is just opposite phase of the opposite side? Probably quite small sweetspot though, problem solved by introducing some more.
 

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OK, so the bug has bit. Thanks guys!

DSC03240.JPG


This is SDA plus center mono. Mono speaker is dipole. I'm impressed with the sound. My class D amp isnt entirely happy with the (+) of channel A to (-) of channel B connection, as channel A and B are carried by two different chips and this cant be changed, AFAIK. It makes a low level of white noise with no signal...it isnt happy turning on into that connection. At least is hasnt blown up.

The center is an maybe a 6-8 Ohm speaker, a CHN-50. It's a little forward connected straight across; 4 Ohms in series balances the sound to a more subtle level. It's all just an experiment, stoked by the discussion here.

The SDA part is simple, the silver speaker on each panel is in series with the copper one on the opposite panel, out of phase. Silver speakers are baffled, copper ones are OB.

So what do I do now? Put the thing on a 3rd 20 X 20" panel? That wouldnt be not leaving much space "uncovered" for any image to form in there.
 
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Yeah it was in Polk manuals that amplifier should be common ground. As the interconnect seems to have only to conductors the amp ground is shared I believe.

If its just SDA and series connection without any matrix thing you are running you could run full wiring to both sides and avoid issues with classD amps. If its three speaker system it requires some matrix somewhere though.
 
Doesn't get better than naked driver(s) ;) Have you been tuning the system further?

Stumbled upon Bacch system on another forum, which to me looks modern more refined version of Polk SDA, with head tracking and all, sold for Hi-end market with Hi-end price. https://www.theoretica.us/bacch-sp.html

Thought about the SDA one evening while trying to get sleep and got to conclusion all one needs is quite narrow bandwidth for the "outer driver", that is supposed to prevent the actual LR sounds to arriving both ears. There is no point to send all the low end to the other side, say longer than 4x head width wavelengths, because the bass would cancel. The top octave(s) is probably not too important either because they are probably that meaningful in the context, head shadowing and directivity at play. So, some kind of bandpassed signal for the the outer drivers is fine. Perhaps this is why Polk SDA is three way per side + two way dimensional section.

Modern version of this concept could use just the main set of speakers without the extra dimensional drivers, just use DSP. FIR filters to tailor the dimensional portion so that its effective enough before going to extemes and make gimmicky, band passed signal without issues from group delay and what not.

Anyone tried doing SDA / Bacch kind of thing with DSP?
 
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