I have been very impressed with a L-R, L+R, R-L array. I agree with many of your "no-nos" except the 60 degree spacing and the center time delay. Try putting all three speakers very close together - like 1 foot spacing between the tweeters. Put them all in a straight row. Don't time delay the center and sit about 8 feet back from that. No need to weight any levels - just straight channel mixing. I get an excellent width soundstage when I do that, and much better clarity than spacing the speakers further apart. I have not yet heard from anyone else who has tried it but it sounds like you could try it easily because you're already doing the channel mixing capabilities and 3 identical speakers to work with. I'd be interested in getting your impressions, good or bad. I need some frame of reference from other critical listeners to tell me what they hear that they like and don't like about that arrangement. Can you hear the excellent sound stage like I do? Am I nuts? The only feedback I've gotten so far is from non audio oriented friends and family. My friend said it's as good as any stereo he's ever heard. My nephew said the surround effect was amazing. It's not surround, but I knew what he meant. The whole front of the room is filled with apparent sound sources.
Glad you found something you enjoy so much!
Like i said in my full post, i've tried various spacings between speakers. Any much tighter than a 60 degree spacing squishes my sound field down to 'why bother with center'.
My speaker are large, about 3 ft wide...so the tight pack idea you use is a non starter for me anyway. And 8ft listening is simply too close.
I've also played with whether to delay the center or not, to equal the arc distance to left and right. (I don't have the room depth to physically deepen center).
It definitely helps me to delay to arc....i think the Gerzon matrixing depends on it.
How far back are you listening?
With your 3 foot wide speakers placed right next to each other you'd need to get 24 feet back for optimally strong stereo effect, which for me was highly unintuitive. The ratio is 1 to 8. 1 foot spaciing means a minimum 8 foot listening distance, otherwise interference patterns are not well organized and the stereo effect starts to get confused. Once you get far enough back the patterns line up with the appropriate ear for strong, clear stereo. As you keep moving further away the level difference in each ear starts to diminish until at some distance it just acts like a mono point source. With 3 foot spacing you should still be hearing good stereo as much as 40 feet back. I've never actually gotten far enough back from a 1 foot spaced array to get the sound to collapse to mono. I'd probably have to take it outside.
I listen at around 14-15ft, with left and right about 22 ft apart for about a 75 degree angle.
This is when using a center speaker. For plain stereo, I set up more towards 60 degrees.
1 to 8 ratio???? Doesn't that equal a little less than an 8 degree angle left to right?
That's a long waay from the typical 60 degree equilateral starting point, for stereo...
Am I misunderstanding ?
You are not misunderstanding. What happens is you get some interaural crosstalk cancellation because the interfernce patterns work out once you're far enough back. You get a wide stereo spread as a result of volume difference at each ear and delayed phase in the quieter ear. It's really amazing. I've been experimenting with mixing in regular 60 degree or more spread stereo. In the mids and highs the regular stereo cannot hope to compete. I use corner horn speakers from 200Hz down crossed over at 24dB/octave. Above that the center array provides much better stereo. The only reason I'm using the corner horn bass is that's what I happen to have for bass.
This is similar to the ambiophonic arrangements where they use two speakers close together and then use digital crosstalk reduction to create a wide stereo soundstage. I thought three speakers like this might provide some strereo effect if the speakers were properly aligned. To my surprise it worked much better than I expected, and the exact width of the array didn't seem too important as long as I got back an appropriate distance from it. I was shocked and had to simulate the array in a wave program to see what was happening. That's where I could see that at about 8:1 you get great stereo separation over a wide range of frequencies.
From the wave simulation I concluded that you should get the drivers as close together in the tweeter range as you can, and then spread the lower frequency drivers further apart. I tried that but it doesn't sound as good. The coherency with all the drivers the same distance apart is better, and the stereo effect is ample.
I think your speaker setup is emulating a "soundbar", that bounces its sound off the reflective surfaces within the room to give off some interesting sound effects.
https://build.com.au/how-soundbar-works
It's definitely not getting stereo from bouncing sound. I've tested this by putting a lot of absorption panels around the speaker array. I work at ASC and we have sound room with plenty of acoustic absorbers on hand. I knew this would be the case but I needed to hear it just to make sure because you're not the first person to suggest it. You can tell when you listen to it that it's much more precise and clear than anything you'll get from bouncing effects. But you can make a good soundbar with this approach that will even work outside or in a relatively anechoic room. The only downside is the stereo effect really only works when you're sitting on-axis. Off to the sides it sounds mostly like mono and you'll be hearing some comb filtering, although not as bad as what you hear with a regular 2 speaker listening triangle.
Well, if you're so confident then I have to try. However, I have a feeling that I'm going to hear everything from the middle. I shall let you know anyway. Meanwhile let us wait for Mark.
Hi guys, it's interesting. My reaction was also it's gotta be a soundbar type thingy.
I think we have to admit, the 1 to 8 ratio does fly against all conventional stereo placement wisdom.
I'd like to quickly stick some speakers close together, but it's not really possible now for me to move my large speakers next to each other. So I'll have to put it on a try someday list.
I think we have to admit, the 1 to 8 ratio does fly against all conventional stereo placement wisdom.
I'd like to quickly stick some speakers close together, but it's not really possible now for me to move my large speakers next to each other. So I'll have to put it on a try someday list.
I'm excited you're willing to try it. Any small bookshelf speakers should do the trick. I've tried it wtih Sony SS-CS5, Revel M16, some little tiny Revel speakers of some kind, and some JBL HDI1600. Worked on all of them. I do recommend a separate approach for bass below 200 Hz or so. The side channels will not produce much bass because it cancels out. Still, you'll hear the stereo separation.
I had a friend over yesterday and let him sit in the sweet spot, so I sat off to the side. Off axis just turns into mostly mono with a slight spacious effect but no real imaging. So that's a downside. A spaced apart up-mixed array is much better for providing stereo separation at more listening positions.
I've been listening to my setup after making some changes and with 1 foot spacing I'm getting better imaging at about 7' distance to the speakers. Also absorbing sidewall reflections seems to help bring out maximum stereo effects, with more sounds reaching out toward a full 180 degree soundstage. So 8 to 1 is a rough rule of thumb on the spacing/seating distance, and side reflections aren't necessarily helpful. It can depend on a lot of factors. Since I'm close to a wall behind me, moving forward a foot might be helping a little.
Because I'm pushed for space in here I'm trying to push the speaker as close to the wall as possible. I hung the TV so I could get rid of the stand it was on, and put some absorber panels behind the open baffle arrangement. I also cut the legs down on the baffle stand so the TV could come down lower. It's a lot nicer to watch but I think the sound quality suffered just a little from all this. Still, the imaging is great. Center array is crossed over at 220Hz, 24dB/octave. So the corner bass cabinets do also provide some stereo effect. Guards added on top the woofers to lead the toddlers not unto temptation.
Edit: Just a few minutes after writing this it occurred to me I could easily pull the array forward, so I did, getting it the recommended 3 feet off the back wall for dipoles. Now I'm more like 6 feet back, and the imaging is excellent, and overall sound quality is too. So if there are any issues sitting this close to the array, they are overridden by the benefits of better direct to reflected ratio. Moving my head forward I'm still getting great imaging at 4 feet, so 4 to 1 gives good stereo results. 3 foot wide speakers only need 12 feet listening distance for this scheme!
Because I'm pushed for space in here I'm trying to push the speaker as close to the wall as possible. I hung the TV so I could get rid of the stand it was on, and put some absorber panels behind the open baffle arrangement. I also cut the legs down on the baffle stand so the TV could come down lower. It's a lot nicer to watch but I think the sound quality suffered just a little from all this. Still, the imaging is great. Center array is crossed over at 220Hz, 24dB/octave. So the corner bass cabinets do also provide some stereo effect. Guards added on top the woofers to lead the toddlers not unto temptation.
Edit: Just a few minutes after writing this it occurred to me I could easily pull the array forward, so I did, getting it the recommended 3 feet off the back wall for dipoles. Now I'm more like 6 feet back, and the imaging is excellent, and overall sound quality is too. So if there are any issues sitting this close to the array, they are overridden by the benefits of better direct to reflected ratio. Moving my head forward I'm still getting great imaging at 4 feet, so 4 to 1 gives good stereo results. 3 foot wide speakers only need 12 feet listening distance for this scheme!
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I finally took a measurement of the SPL difference I'm getting from left to right ear. The chart below shows the level reduction in the right ear compared to the left ear for a left panned signal in my 3 speaker array. It's not natively quite this good, but tonight I managed to successfully apply recursive crosstalk reduction to the side channels.
!!!
This is a total trip. I contacted Rogue Aeomeba asking if they knew a way to do sample level delays in Audio Hijack.
They gave me the link to this free AU component that does the trick: https://www.voxengo.com/product/sounddelay/
This lets me apply a 3 sample delay, which is about right for recursive crosstalk elimination at 48kHz sample rate. I played with the normal recommended sound reduciton of 2 to 3 decibles but it just sounded confused. Then I realized that I already had a head start because of my 3 speaker array inherently creating some crosstalk reduction. I measured that to be around 7.5 to 15 decibles, so I initially reduced it with roughly appropriate EQ curve and then applied successive recursions with -2.5dB.
Eureka!
I think this is a big step up for this array, and it has an advantage over recursive crosstalk with a 2 speaker system for two reasons:
1. The center signal is completely untouched by the recursion alogrithm.
2. The alogrithm starts off much quieter so it has much less audible effect when listening off axis and less troublesome effects on tonality overall. To my ears it sounds cleaner and more natural than without it.
I'm getting excellent width now. A left panned sweep sounds like it's completely off to my side, 180 degrees! I can probably get it better with a little more measurements and experimentations.
!!!
This is a total trip. I contacted Rogue Aeomeba asking if they knew a way to do sample level delays in Audio Hijack.
They gave me the link to this free AU component that does the trick: https://www.voxengo.com/product/sounddelay/
This lets me apply a 3 sample delay, which is about right for recursive crosstalk elimination at 48kHz sample rate. I played with the normal recommended sound reduciton of 2 to 3 decibles but it just sounded confused. Then I realized that I already had a head start because of my 3 speaker array inherently creating some crosstalk reduction. I measured that to be around 7.5 to 15 decibles, so I initially reduced it with roughly appropriate EQ curve and then applied successive recursions with -2.5dB.
Eureka!
I think this is a big step up for this array, and it has an advantage over recursive crosstalk with a 2 speaker system for two reasons:
1. The center signal is completely untouched by the recursion alogrithm.
2. The alogrithm starts off much quieter so it has much less audible effect when listening off axis and less troublesome effects on tonality overall. To my ears it sounds cleaner and more natural than without it.
I'm getting excellent width now. A left panned sweep sounds like it's completely off to my side, 180 degrees! I can probably get it better with a little more measurements and experimentations.
Following up on my previous post about using recursive crosstalk reduction to improve the stereo width of the 3 speaker array, I've found that there is a price to pay for this in terms of sound coloration. I've never been happy before with RACE style crosstalk elimination becuase of side effects in the implementations I've heard of it, so I consider it a "nice idea, too bad it's got serious problems" kind of thing. I think there may be really good implementations that can pass the sound purity test, but it seems like a hard ask considering how it works. Off axis is likely to get weird, and you have to be in just the right spot, so advanced systems end up with head tracking and calibration with in-ear monitors. I think I'm getting excellent, natural soundstage width that works well with all kinds of recordings with just the three speaker array, channels mixed and no further processing. It sounds pure and clean - better than just two speakers can do because they are blighted with severe crosstalk of the phantom center image. The soundstage is limited to the sweet spot but I don't have to have my head in a vice. No time delays are necessary. The whole thing can be pulled off to a very high degree of fidelity with purely analog circuits if someone wished.
I did some work tonight with REW, calculating the predicted combined response at each ear based on the differences in timing of each signal from the 3 speaker array with about 1 foot spacing and listing about 7 feet back to a side panned signal. I think this clearly shows why it works so well. Below 1000 Hz it's mostly phase that gives us directional info. At 1500Hz it's a mix. By 2000 it's mostly level difference. You can see that the array starts to create a level difference around 1000 Hz that gets stronger for a while until it looses power, and eventually at higher frequencies actually goes backwards. This has prompted me to roll off the extreme highs on the side channels. I thought I was hearing that! My attempts at measuring were showing that reversal too.
In any case, I think this calculated response difference of between each ear for a side panned signal provides a solid explanation why the 3 speaker array works to create a wide stereo soundstage. This doesn't show the phase difference that's happening below 1000Hz, but it is happening. I should add that I think if you start getting strong level differences below 1000Hz through recursive crosstalk reduction it's going to create a strong impression of sound sources right next to your ear, because that's normally the only way that can happen. So it's great for special effects, but for normal musical listening we don't need that much crosstalk reduction.
In any case, I think this calculated response difference of between each ear for a side panned signal provides a solid explanation why the 3 speaker array works to create a wide stereo soundstage. This doesn't show the phase difference that's happening below 1000Hz, but it is happening. I should add that I think if you start getting strong level differences below 1000Hz through recursive crosstalk reduction it's going to create a strong impression of sound sources right next to your ear, because that's normally the only way that can happen. So it's great for special effects, but for normal musical listening we don't need that much crosstalk reduction.