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Stereo Crosstalk Elimination (reduction) Par Excellence!

beagleman

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I think the problem with SDA was most people who owned it, like myself, never got it set up correctly. I think it's super finicky in terms of aligning the speakers with the listener's ears accurately, and that's hard to do when the speakers are spaced far apart like in a normal stereo system. And even when I've gotten their method to work well in my own experiments with the speakers all right next to each other, it tends to sound too "busy."
SDA set out to solve something that never was an issue.
They explained SDA in their "White" papers by giving an example of a concert hall with 2 mics set up like where are ears are on our heads...............

Therein lies the issue. They are trying to "Fix" regular stereo speakers, but with the assumption that recordings are made in the manner described above which is what Binaural is basically.

They never explain or account for how SDA will work with the 99% of recordings that are NOT binaural or made with 2 mics spaced 7 inches apart.

Just a great idea, but to fix something that is not broken. Polk was great at marketing and making things sound like they were more than they were.
I have owned SDA speakers, and with NORMALLY recorded stereo they create a false, unusually odd and wide image.

Sure it may sound "Better" than regular stereo in some fun ways, but never sound correct, especially when one knows how the recording was done or was supposed to sound.
 

fineMen

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If you're reasonably centered you get good timing differential for panned signals, which may explain why it can generate such a wide sound field with very good separation and solid imaging all the way across.
Thanks for the idea. I'm not so much into the celebration of stereo, but my focus is more the dynamics, means less reverberation. So I ended up with pretty huge horn loaded speakers. It then came to me, that I actually suffer from the viced-in listening posture. And additionally the horns subdued the mids to treble in the indirect soundfield. An aditional center came in handy. I'll try a spin off of your proposal!
 
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Tim Link

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SDA set out to solve something that never was an issue.
They explained SDA in their "White" papers by giving an example of a concert hall with 2 mics set up like where are ears are on our heads...............

Therein lies the issue. They are trying to "Fix" regular stereo speakers, but with the assumption that recordings are made in the manner described above which is what Binaural is basically.

They never explain or account for how SDA will work with the 99% of recordings that are NOT binaural or made with 2 mics spaced 7 inches apart.

Just a great idea, but to fix something that is not broken. Polk was great at marketing and making things sound like they were more than they were.
I have owned SDA speakers, and with NORMALLY recorded stereo they create a false, unusually odd and wide image.

Sure it may sound "Better" than regular stereo in some fun ways, but never sound correct, especially when one knows how the recording was done or was supposed to sound.
I would argue that Polk's method has some merit beyond that simple case of the Binaural microphone setup. I'm not willing to make the strong statement that regular 2 channel stereo is "broken." But if not at least flawed, it is heavily saddled with 2 channel crosstalk. If you prefer that, great! Those of us who don't prefer it start looking for things to do about it. Getting better stereo separation improves the sound of a lot of recordings in my opinion. I think the better solution however is to add more speakers. Even perfect stereo separation suffers from HRTF issues unless the panning is also accompanied by customized HRTF curves. If there's a real speaker sending sound across your head at the right angle, the problem goes away!
 
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Tim Link

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Thanks for the idea. I'm not so much into the celebration of stereo, but my focus is more the dynamics, means less reverberation. So I ended up with pretty huge horn loaded speakers. It then came to me, that I actually suffer from the viced-in listening posture. And additionally the horns subdued the mids to treble in the indirect soundfield. An aditional center came in handy. I'll try a spin off of your proposal!
I am also the owner of giant horn speakers, for the same reason as yourself. I also noticed that the narrower I made the treble dispersion the more head-in-vise the situation became. I ended up with wider dispersion horns for that reason and because I actually wanted a little more reverb back. Now I'm moving into another house and things are all in shambles. The big horns are in pieces out in the garage with no place to go until I get other stuff moved out. I think I will also try this arrangement with horns when things get under control.
 
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Tim Link

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After listening to a lot of Atmos music in 5.1 channel configuration, and in stereo with up-mixing using Pro Logic, I decided to re-visit this speaker array. I've finally figured out that I can control up to 8 channels of output on my Mac using Audio Hijack, so I can get control over each amp in my Denon receiver over HDMI! That gives me a lot more control over each speaker and lets me put stereo mid bass signals below 200Hz back into the side channels. This restores tonal balance and is a big step up in the sound quality, and to my ears bests the multi-channel arrangements like Atmos or Pro Logic up-mixing, at least with the low end equipment available to me right now. It's just beautiful. Over in the Atmos threads there is some good talk about newer Atmos music mixes having restored dynamic range, but to my ears they're not always better. I thought the HRTF improvement of a spread out speaker array might make it better than what I'm doing with this "crosstalk elimination" array. It might potentially be better, but it seems to have it's own problems because of how it's mixed. They're trying to keep some of that stereo crosstalk sound by forcing a center phantom image even when you've got a center channel. Might sound really good sometimes, depending on who you are and your mood.

I've now got a 5 speaker array at home and a 3 speaker array at my work desk. Up close 3 speakers is enough. 5 speakers allow you to get back further and still enjoy the effect.
 
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Tim Link

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OK, I take back the part about the speakers needing to be right next to each other at ear distance apart. My desktop system at work is just brilliant with the speakers spread out from each other and the outside speakers moved forward to adjust the timing. This totally solves the problem with needing narrow speakers. Any 3 great speakers can be used and they won't mess with each other's baffle front or reinforce each other, and it's not super difficult to get the time alignment right. You can do it by ear. It's easy to tell when it's working right with a simple left/right speaker test. The spread helps with HRTF. It's great! With this arrangement it only works best at one particular distance but that was the case with them all together too.
 
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Rip City Dave

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This vintage device works well for me.

s-l1600.jpg
 
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Tim Link

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This vintage device works well for me.

View attachment 248355
Nice to have a single box that does the trick! And, it works with just two speakers. I used to have a Carver Pre-amp that had that Hologram mode. It was a nice pre-amp all around, with lots of settings for various types of phono cartridges. I really liked it. I have to say though I never got the Sonic Hologram to do anything that I could hear as interesting. I think I did not understand the concept and did not get the speakers set up to take advantage of it. I don't think I really understood what to listen for either. Come to think of it I don't recall ever hearing a problem with the phantom center image being off to one side, or the sound stage being wrong in any way. I payed very little attention to the accuracy of speaker placement or my listening position. I was never thinking about such things back then. I sometimes miss that innocence.

I wonder if that Carver Sonic Holography matrix is available in software form? It'd be cool to try as an AudioUnits Plug-In.

How far apart do you have your speakers with the Holography running? If it works like I think it does it seems you could have them a bit closer together than usual. I've used RACE software before and that allowed me to have the speakers very close together while still producing a very wide stereo effect.

After I discovered the improvement from spreading the speakers apart in my office at work I came home and did the same thing. This is great because now I can immediately switch between my 3 channel matrix, or 2 channel stereo, or various surround formats without moving speakers or re-wiring anything. Just a few clicks on the computer and it's done. So far, to my ears, my 3 channel matrix beats standard 2 channel hands down, and usually beats even discreet multichannel mixes. But I think that's mostly because I don't like how they usually do those mixes for music. They maintain a phantom center image by not using the center channel much for center panned vocals. The phantom center is something I'm wanting to get rid of! Multi-channel movie and game soundtracks are usually great. They put the center vocals where they belong. But so does the 3 channel matrix so I'm not highly inclined to switch over from stereo to 5.1 discreet unless other people are watching with me.
Switching back and forth between 3 channel matrix and 2 channel with phantom center is interesting. I can see why people like the phantom center. It has an effect. I would liken it visually to a somewhat transparent apparition between the speakers, with an overlay of the same apparition slightly smaller and dimmer and flipped the other way right on top of it. And then a big fuzzy spread from left to right of something hard to explain visually which I'll call "glow" for now, but I think it comes from the HRTF mismatch between the sound seeming to come from straight ahead but actually hitting the ears at angle from the sides, where each speaker is located. It's kind of nice sounding in its own way. It's the inescapable but also potentially lovable sound of 2 channel playback.
 
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Rip City Dave

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My Magnepan speakers are four feet from the back wall, 9 feet apart and 9 feet from listening position. When you turn on the Carver C9, the soundstage widens dramatically beyond the speaker width. Imaging is a little sharper, too, but not greatly so. I like it, but it is recording dependent.

There is something to eliminating cross-talk . In the case of the C9, it uses constructive interference in the signal in order to achieve the cancellation.
 
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Tim Link

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I've been obsessed with this matrix up-mix for weeks now. The latest change was to move the speakers back to a more standard, separated arrangement with the center channel moved back to time align with the side channels at each ear. This allows for a very good standard 2 channel arrangement that I can instantly compare by turning the matrix on and off. The two channel setup is working very well, with good center image and side images projecting beyond the speakers. So this presents a better representation of what a good stereo mix can sound like, and it's brought me back down to earth about the plusses and minuses of a derived center channel. The truth is, the 2 channel really is better sounding in terms of tone on a lot of material, and for me tone wins every time. So I started messing with equalization and other settings in the 3 channel matrix to try to bring it closer, and discovered that I really couldn't do it for two reasons. The first is that the bass is all messed up if all the bass comes out of the center channel but not the side channels. The second reason is that when mono is summed it will dull the highs on many recordings, which causes center panned sounds to be dulled while sounds panned to the side are bright - maybe too bright sometimes. So it occurred to me that the highs and the lows need to be left in standard stereo, with only the midrange being subject to the L+R center, and L-R, R-L signal on the side channels - which Polk had figured out with their SDA arrangement. After some experimenting I've found that something along the lines of 500Hz to 6000Hz is a good range to limit the matrix to. The matrix adds energy in that range so the total volume of the matrix needs to be reduced a little. I did it by ear as I'm not really sure how to calculate it with all the negative and positive signals mixing. I think it comes out to something a little less than 3dB.

So now I've arrived at a hybrid arrangement that is better than standard 2 channel almost every time, with often better tone in the midrange for center panned sounds because it's smoother and fuller due to the comb filtering being removed, and the imaging is at least as wide as with the standard 2 channel playback but the center is much more solid.

Is it worth the price of an extra speaker and the requirement for a matrix mixing and equalizing step in your digital playback chain? I can't say for sure. Even the basic matrix with no equalization can really sound great on some material. I need to hear it on more systems, especially systems that are really sounding great already in standard 2 channel configuration. I should be able to do this when I get my horn system running again. All I have to do is buy one extra horn and one extra driver for the center channel, which now only has to produce the midrange.
 
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Tim Link

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Continuing to experiment with this I've come to the conclusion I really don't understand exactly how it works. I've discovered to my utter surprise that the spacing between the side channels and the center doesn't seem too connected to the distance between my ears, so time alignment isn't working the way I think it does, or isn't nearly as critical as I would have thought. The speakers can be spread way apart and still produce excellent left/right spread but this can lead to some dullness in the center panned sound because of summing stereo to mono in the center channel, (I think.) The stereo brightness and airiness can be preserved in center panned sounds by keeping two of the side channels within a foot to either side of the center. The stereo imaging at about 1 foot tweeter distance is excellent and very stable with distance compared to having the speakers closer together. So, that's great I guess! There can and should be about a foot between the speakers. I totally don't get why. If anyone can explain this I'd be appreciative. I really don't understand it but it sounds great.

I did some further experimenting with adding two widely spaced side channels playing standard stereo. I tried running the side channels full range, and then found it really works better if they are kept to midrange frequency and below duty. I tried using a high pass on the center 3 channel array to keep them from playing the same frequencies as the outboards and that was pretty good. Better still is to run the wide channels in the L-R , R-L matrix instead of standard stereo but low passed at 500Hz, and don't high pass the center array. The wide channels need to be boosted about 3dB above the center array, and then the tone becomes really good and the stereo imaging really great.

So this is where I'm at now, a 5 speaker array with the center 3 center speakers on 12" center spacing and the outboard speakers about 6 feet further out and running the same signal as the inboard side channels but only from 500Hz on down. It's really quite amazing how with wide panned material the sound all seems to be coming from the side with no hint that any of the middle or opposite side speakers are making any sound even though they are. You'd swear those side speakers are putting out full range sound with sparkling highs, even though they're not. Having the lower frequencies coming from far to the sides really works some magic, filling that range in sweetly without sounding muddy and murky.

Below you can see the array as it's set up now to take advantage of all 5 channels on the Denon as well as the bass channel which is down in the lower left corner. This Audio Hijack application is far more powerful than I realized when I bought it. I can get full access to each channel on a 5 channel or 7 channel receiver over HDMI, with full crossover and parametric EQ, 31 band graphic EQ and some other effects on each channel, as well as all kinds of mixing features.

Screenshot 2022-12-10 at 3.18.15 PM.png
 
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Tim Link

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After a lot more experimenting I think I understanding now what's happening - why this 3 speaker array produces excellent stereo imaging regardless of the spacing of the speakers, and why a particular spacing will probably be best depending on your speakers and your listening environment.

To start with I'll show what happens with a standard two speaker array producing a center panned image. The three speaker array just uses a single speaker for center panned material so there are no interference patterns so I won't bother showing that. This first picture shows a 2 d simulation of two speakers playing the same signal. What you see is a circular pattern seemingly emanating from the center of the 2 speaker array, with comb filtering that results in lobes that always arrange themselves with a center lobe forming perpendicular to the plane of the speakers. So if you had just one ear and placed that ear directly between there would be no comb filtering. But since we have two ears our ears sometimes end up in the cancellation zones depending on the frequency. Notice the lobes are fairly even in intensity.
Screenshot (19).png


Below are some pictures of simulation of the 3 speaker array playing a signal panned to the top of the array. Notice how the lobes in the next three pictures are always arranged so that there is always a null right in the middle of the listening triangle instead of a lobe, or peak. Notice how also the lobe on top is louder than the lobe on bottom, and leads it in phase. This holds regardless of frequency, which means it also holds regardless of speaker spacing. So that explains why the stereo imaging remains excellent despite the spacing.

Screenshot (20).png


Screenshot (21).png
Screenshot (22).png

So if various spacings work, which spacing should we choose? Well, I found out that as the speakers are pushed closer together the tone gets brighter. By spacing them further apart the tone can be adjusted to sound natural. It works really well for me at about 1 foot spacing. Another important factor for adjusting both the tone and the stereo imaging is the loudness of the center channel compared to the side channels. I find it needs to be down 3dB, which is what I've shown in these simulations.

So I've got it sounding really excellent now with just 3 speakers and I'm not using any equalization to compensate for the array's tone. I don't see a need or even obvious benefit to using any more than 3 in the array. Three's the Bee's Knees for 2 channel stereo playback! Turn the center channel down a little and space to taste.
 
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Tim Link

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Still working on this. I've found a very satisfactory solution for tonality issues with this 3 speaker array. With the speakers separated you can assume that if your speaker of choice is good or properly equalized as necessary, the tone will be correct for center panned sounds because those are just playing through that one speaker. When the tone is panned to the sides is where the difficulties arrive because there's one speaker playing out of phase, increasingly cancelling some of the bass produced by the other two speakers as the frequency goes down.

The solution turns out to be the obvious one - just shelf up the bass on the side speakers only (not the center!) How much you need is going to depend on how far you have the speakers spaced apart. The easy thing to do is play CORRELATED pink noise and pan it from center to the left and right. It will sound brighter and thinner as it moves to the sides. Adjust the shelving amount on the side speakers and the volume on the center speaker until the panned pink noise moves across the sound field with minimal apparent change in tone and volume. I ended up with the setting below with my 13 inch spacing. This is making sense! Once below 100Hz the subs take over so no point in further gain, but you can see the need for gain starts around 500Hz, and it's a good 7dB or so gain required by 100Hz. Hey, 13 inches is 1/2 wavelength of 500 Hz! I think this is making sense. As the speakers are spaced further apart the shelving will start at a lower frequency.

At this point this array is really sounding great! I can whole heartedly recommend giving this a try. I've also found some decent EQ to correct the tone of the SSCS5 so combining that with this side channel shelving is really making for an enjoyable listening experience that's way beyond anything I ever expected from 3 cheap Sony bookshelf speakers and a cheap Denon receiver, and two cheap subs.


Screenshot 2022-12-15 at 11.33.43 PM.png



I've always loved Al Petteway's Caledon Wood album but the guitar never sounded quite right on my big horn rig. Now for once I'm really satisfied with the sweet, natural tone I'm hearing.


I'm still living in squalor at my new house, with the TV on the floor, the receiver hidden behind the TV and the speakers sitting on a board on top the receiver. There's half emptied cardboard boxes out of view of the camera. And yet this is just producing wonderful sound. Tone AND imaging are just wonderful!
three channel array.jpg
 
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Tim Link

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I've started a thread on this at DIYaudio.com https://www.diyaudio.com/community/...-for-the-phantom-center-image-problem.393540/

This really is magic for me. It's what I've been looking for the last 20 years and it's so freaking simple! The general guideline for set up is to put the 3 speakers about 1 foot apart center to center and set the listening position at least 8 feet back. The patterns setup consistently by that distance and it just works! I got what I want for Christmas!
 
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Tim Link

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The latest iteration - still using the Sony SS-CS5 but got them snugged up inside an old TV cabinet I bought for my mother decades ago - when CRT TVs were still all the rage. There are black towels between and above the speakers to get rid of the hollow sound of the cabinet. Also the center channel down below is just filler for the same reason - keep sound from bouncing around in there. Stuffed animals too, which also belonged to my mother. She liked buffalos and reconned she was a Native American in a past life. Off to the sides are the horn loaded woofer cabinets. They're serving duty 100 Hz and below. They need to be turned down 15 dB at the crossover to match the Sonys! at 20Hz they're only turned down 3dB, which means they're still more efficient than the Sonys even down there - assuming I've actually got flat response that low. I haven't measured carefully yet but it sounds like there's plenty down there. They're just being powered off the surround channels on that Denon and they can shake the house! There are four 18" woofers in their own 6 foot long folded horns in each stack. I don't think it's overkill. Anybody got a weirder system out there? This is a lot of fun to listen to. Nice wide clear imaging now with majestic bass! Honestly the little Sonys get loud enough to meet my needs although about when I'm starting to get worried about my hearing safety the do seem to be starting to strain. I was worried these bass stacks would not fit under the ceiling in this new room. I pulled up the old carpet and underlayment, which was 47 years old and terrible smelling, and put in thin carpet tiles and as you can see it worked out.
PXL_20230119_044801757.NIGHT~3.jpg
 
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Tim Link

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I got some Revel M16 speakers! There's a dealer in town that let me borrow them for an audition. The white one in the middle was an accident but I think I like it! I have a strong feeling I'll be keeping them. I just got them installed a few hours ago but I'm getting a very good impression of natural, full, rich, solid sound. The SSCS5s sound a little rough around the edges in comparison.
PXL_20230201_042951250.NIGHT.jpg
 

ernestcarl

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If I had three identical spare speakers I'd probably want to try this out. Oh, well... I do use a tiny little Fostex 6301 as a makeshift center channel for my desk, but the effect is not at all the same as I'm simply summing the left and right channels into the center at a far lower SPL level -- simple as it gets... main purpose only to increase forward center focus and imaging of vocals as desired.
 
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Tim Link

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If I had three identical spare speakers I'd probably want to try this out. Oh, well... I do use a tiny little Fostex 6301 as a makeshift center channel for my desk, but the effect is not at all the same as I'm simply summing the left and right channels into the center at a far lower SPL level -- simple as it gets... main purpose only to increase forward center focus and imaging of vocals as desired.
If you do try it at some time I'll be very interested in your impressions. I've found it is effected by room acoustics quite a bit. In this current room which is rather narrow I'm not getting a really wide stereo effect. I'm also starting to think the phantom side images are somewhat unsatisfying to me in the same way a phantom center is. I'm becoming more attracted to the idea of spacing the speakers further apart and time aligning for a specific listening distance, as was discussed somewhere earlier in this thread. I tried it at my work setup today and it was working well. I pushed the center speaker back until the pan control in Audio Hijack produced a very strong left and right panning effect. To do that at home with the M16s I'll need to come up with some speaker stands.
 

Big man on the Fox

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I have recently added HAF /Home Audio Fidelity room correction. They offer a friendly solution for adding cross talk cancellation with measurements of your speakers and then filters are created by them. For an investment of $200-300. you have a solution which integrates with most music players. Ie. Roon , J River… Higly recommended!! You would also want their basic filter. Too much to explain here. Check it out, you won’t be disappointed!
 
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Tim Link

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I have recently added HAF /Home Audio Fidelity room correction. They offer a friendly solution for adding cross talk cancellation with measurements of your speakers and then filters are created by them. For an investment of $200-300. you have a solution which integrates with most music players. Ie. Roon , J River… Higly recommended!! You would also want their basic filter. Too much to explain here. Check it out, you won’t be disappointed!
Thanks! I'll check that out.
 
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