Getting the full SDA Effect from Polk L800 Speakers

TLS Guy

TLS Guy

Audioholic Slumlord
I would suggest reading the science behind the idea before dismissing crosstalk cancelation as a gimmick or false effect. Your explanation is actually making a false comparison. You are assuming that the way we hear actual instruments matched how we hear those instruments reproduced over two speakers. It’s a very common anti-SDA claim but it’s not correct. You don’t have to like it, but crosstalk cancelation is an area of significant research for a reason. Not by knowledge less neophytes starting speaker companies but PhD researchers searching for a better understanding of how to recreate 3D sound.

the natural crosstalk that you hear when you hear a real instrument is already baked into the recording. The crosstalk you hear in a room with speakers is not natural. It’s not supposed to be there.



Look at what they reference and find those papers as well. You will see that this is based on sound science.

the holy grail for accurate sound reproduction is high order ambisonics and those systems rely on high directivity speakers and digital XTC. that is because it is most accurate and realistic when there is minimal crosstalk. It’s a distortion.
These papers are talking about something a lot more complex, than sending a passive reverse phase signal to some outside drivers.

To do this, even if you think it desirable, which in my view is highly questionable, would take extensive active DSP processing as mentioned in the papers.

For one thing I don't see how a passive network will not send an inverse phase signal to a set of drivers when the signal to each channels is identical in phase and intensity. That is the characteristic of a dead center signal. You certainly don't want to cancel that in any way. I do not see how those signals can be isolated and not have their phase reversed without extensive and complex DSP.

Even so the sweet spot problem would remain.

The fact is that microphone technique can solve most of these problems. The scandal is that pure Blumlein is rarely used and it should be used almost always in concert halls and large spaces.

I have had no trouble making recordings, that recreate a really good approximation to the original sound field, through good speakers. The DSP of the Dolby up mixers just makes it all the more realistic. With the right source my 7.2.4 system produces and incredibly realistic sound field with the best of recordings. The YouTube video I referenced above is one such.

I strongly suspect that SDA hokus pokus would ruin it.
 
Pogre

Pogre

Audioholic Overlord
I have to agree with Irv, well designed speakers should not need to sound their best in a "weird" sort of placement right?:D Okay if that's just by chance I think, and that it would work almost as good in more typical, commonly practical placement scenarios.
Ultimately any speaker is going to have an optimal placement within a room, and they're not all the same, right?
 
ryanosaur

ryanosaur

Audioholic Spartan
I think it's telling us something when a reviewer buys a pair of speakers they just examined. Whatever the reasoning or logic may be and regardless the true efficacy of the technology in question, that both Poes and Shady experienced these and found something of value in them shouldn't be dismissed.
I'm not going to run out, sell my Phil3s and BMRs, and go all in on a Polk Legend rig just because of the review. I do find it interesting, and a little exciting, that these Speakers elicited the response they did. (Afterall, its not like Poes is a first time poster coming in claiming he found the perfect audiophile solution to all our SQ problems! :p Likewise, this feels different than the effusive praise showered upon the Tekton Double Impacts by a couple early reviewers that claimed to be replacing their previous reference gear with DIs while not supporting their reviews and praise with any measurements to back it up.)
What would be more informative is a follow up review after he is fully settled and has them set up in whatever new system he might employ them, allowing us to see a different setting, what needed to be done to accommodate that proper setup in that room, and more impressions of their performance.
:cool:
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
There is anti-phase information in the speaker outputs of an amplifier with a differential output stage? You're on your own, Matthew.
1617905451629.jpeg

From the article I shared that you did not read. Please explain how this is not a differential balanced output?
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
I think it's telling us something when a reviewer buys a pair of speakers they just examined. Whatever the reasoning or logic may be and regardless the true efficacy of the technology in question, that both Poes and Shady experienced these and found something of value in them shouldn't be dismissed.
I'm not going to run out, sell my Phil3s and BMRs, and go all in on a Polk Legend rig just because of the review. I do find it interesting, and a little exciting, that these Speakers elicited the response they did. (Afterall, its not like Poes is a first time poster coming in claiming he found the perfect audiophile solution to all our SQ problems! :p Likewise, this feels different than the effusive praise showered upon the Tekton Double Impacts by a couple early reviewers that claimed to be replacing their previous reference gear with DIs while not supporting their reviews and praise with any measurements to back it up.)
What would be more informative is a follow up review after he is fully settled and has them set up in whatever new system he might employ them, allowing us to see a different setting, what needed to be done to accommodate that proper setup in that room, and more impressions of their performance.
:cool:
It’s also not a perfect speaker. It has issues. We noted those. I called it a flawed speaker in the video review. I noted it’s problems. I’ve heard speakers with better timbre, better bass, and a greater ease in their reproduction of sound. What I loved and have never heard bettered was their imaging.

that fact that some are dismissing the concept without any understanding of it is a bit beyond me. DSP crosstalk cancelation is not superior to theSDA approach. It’s simply different. Both have advantages and disadvantages. In reality, an ideal system would likely use both. The use of SDA arrays has the ability to created a wider sweet spot in which crosstalk cancelation works. It is also more controlled. DSP will always introduce more significant timbre problems than passive will and until the BAACH that wasn’t something that that has been addressed. BAACH claims to have cracked that nut. However it’s efficacy is highly dependent on the dispersion of the speakers. Working best with very narrow dispersion speakers.

the biggest problem all of these systems have is that the research into XTC found you need at least 20dB of XTC to realize the benefits fully. The Polk SDA method achieves that only under anechoic conditions. Anything less than optimal causes a breakdown. DSP varies. Most of the old methods could only achieve about 5-15 dB and needed to be mixed with other processes to address that shortcoming. BAACH has realized a far greater amount. I believe with very narrow dispersion speakers and optimization of the setup and DSP they have seen upwards of 30dB of XTC. That is simply unmatched as far as I know.
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
I have to agree with Irv, well designed speakers should not need to sound their best in a "weird" sort of placement right?:D Okay if that's just by chance I think, and that it would work almost as good in more typical, commonly practical placement scenarios.
I think the only thing weird is they work best closer together than some like. Most speakers of different design approaches have different placements they work best with. This is likely more common than most realize. The fact that these work well up against a wall and 6’ apart is actually closer to how most people set up their speakers.
 
P

PENG

Audioholic Slumlord
lots of amplifiers have differential outputs in which the negative terminal does not reference ground. All HYPEX, Purifi, and various differential output Class AB amps are of this type. Your statement that all amplifiers are single ended is completely incorrect.


I came to this conclusion because the designer of the speaker told me about the issue. However others on this forum had raised the concern when I started reviewing and was using a fully balanced differential output Cherry Class D amp.
Terminologies sometimes can be confusing, and this seems to be one of those.

There are a) single ended vs push-pull (you mentioned that already), and b) unbalanced/single ended output vs balanced/differential output. I would slightly disagree with you about "push-pull" being also single ended, only because it might create confusion, as Wiki put it: "A conventional amplifier stage which is not push–pull is sometimes called single-ended to distinguish it from a push–pull circuit." So I think it is better to consider push-pull not single ended..
 
P

PENG

Audioholic Slumlord
Ultimately any speaker is going to have an optimal placement within a room, and they're not all the same, right?
Agreed, that's why I said what said, in trying to cover both sides..:D
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
These papers are talking about something a lot more complex, than sending a passive reverse phase signal to some outside drivers.

To do this, even if you think it desirable, which in my view is highly questionable, would take extensive active DSP processing as mentioned in the papers.

For one thing I don't see how a passive network will not send an inverse phase signal to a set of drivers when the signal to each channels is identical in phase and intensity. That is the characteristic of a dead center signal. You certainly don't want to cancel that in any way. I do not see how those signals can be isolated and not have their phase reversed without extensive and complex DSP.

Even so the sweet spot problem would remain.

The fact is that microphone technique can solve most of these problems. The scandal is that pure Blumlein is rarely used and it should be used almost always in concert halls and large spaces.

I have had no trouble making recordings, that recreate a really good approximation to the original sound field, through good speakers. The DSP of the Dolby up mixers just makes it all the more realistic. With the right source my 7.2.4 system produces and incredibly realistic sound field with the best of recordings. The YouTube video I referenced above is one such.

I strongly suspect that SDA hokus pokus would ruin it.
Your making a lot of assumptions based on little understanding of the concept or technology. It has no effect on the center image. It simply eliminates crosstalk. Do headphones have a bad center image? They have no crosstalk.

the original research into this utilized analog circuits to achieve it and it worked fine. It just introduced a timbre shift. One research team used a large board of material that they insured their face into. It too worked fine. Fancy DSP is is simply replicating the SDA approach without requiring an extra set of drivers. What Polk has done is more sophisticated than you realize. You aren’t giving it enough credit.

the benefit of the DSP approach that BAACH has utilized is that it can work with any speaker, but works best with narrow dispersion speakers. It achieves the highest XTC of any approach yet, but I’ve talked with those authors before. They believe the best solution would utilize both as it would widen the window in which high XTC can be achieved. They just didn’t want to make speakers. As I understand it, they had hoped to license their technology to companies that would implement it in their products. If Polk wanted to, they could, but then how do you give up on the history they have doing it their own way. Maybe next time.

you don’t have to want this, but based on your responses, it seems you have never heard it. You have repeatedly dismissed the idea as a gimmick. Unnatural. If you read these papers then you can at least see that it is no gimmick and the issue is real. Your portrayal of crosstalk was incorrect and mischaracterized why this would be desirable and it seems you still hold onto that original idea. In this case, how we hear sound in a concert hall and how that is recreated in our room are not the same. We can’t make that comparison and accurately be describing what crosstalk is. As they say, you are entitled to your opinions, but not your facts. Crosstalk in your listening room is an undesirable distortion. That is a simple fact.
 
P

PENG

Audioholic Slumlord
View attachment 46411
From the article I shared that you did not read. Please explain how this is not a differential balanced output?
Knowing that he has, or had one of those so called fully/truly balanced (end to end/input to output) ATI amp, perhaps it is just a case he missed or just hasn't have his 2nd cup yet today.:D
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
Terminologies sometimes can be confusing, and this seems to be one of those.

There are a) single ended vs push-pull (you mentioned that already), and b) unbalanced/single ended output vs balanced/differential output. I would slightly disagree with you about "push-pull" being also single ended, only because it might create confusion, as Wiki put it: "A conventional amplifier stage which is not push–pull is sometimes called single-ended to distinguish it from a push–pull circuit." So I think it is better to consider push-pull not single ended..
As Irv was correctly pointing out about all of these amps is that they become single ended at the output. What I said is pedantically correct it’s just confusing because we don’t always think about what these terms really mean. A product can be single ended or balanced at various stages. A push pull amplifier is traditionally of a single ended output type. As compared to a differential output amplifier which would require a paid of push pull amplifiers, one inverted.

I am still not clear on what I am missing here. I have passed all of this onto Bruno Putzey to see if he has a better way of describing it or to indicate where I am in error. Given that this was peered and that I had this specific topic discussion with Bruno before, I do think I am right. These are differential output amplifiers and are no different than a differential balanced output preamplifier or dac. Just operating at much high voltages and with floating grounds. Why floating the ground makes it not balanced is beyond me. The fact that one of the amps is flipped in phase means anti phase on that leg, right? What did I miss? It’s still seeking common mode rejection.

1617907027190.jpeg

under common mode feedback in the article I linked, this diagram clearly shows both that it is a balanced output and maybe raises the concern Irv is having? But this is addressable in the design of the amps, and as noted, many balanced output amplifiers exist.
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
@Irvrobinson Gene asked me to share this with you if you still don’t believe that balanced differential output amplifiers exist. But im pretty sure you already own the ATI version which was a better amp yet. Both are discussed in technical detail in the article I linked.

 
P

PENG

Audioholic Slumlord
As Irv was correctly pointing out about all of these amps is that they become single ended at the output. What I said is pedantically correct it’s just confusing because we don’t always think about what these terms really mean. A product can be single ended or balanced at various stages. A push pull amplifier is traditionally of a single ended output type. As compared to a differential output amplifier which would require a paid of push pull amplifiers, one inverted.

I am still not clear on what I am missing here. I have passed all of this onto Bruno Putzey to see if he has a better way of describing it or to indicate where I am in error. Given that this was peered and that I had this specific topic discussion with Bruno before, I do think I am right. These are differential output amplifiers and are no different than a differential balanced output preamplifier or dac. Just operating at much high voltages and with floating grounds. Why floating the ground makes it not balanced is beyond me. The fact that one of the amps is flipped in phase means anti phase on that leg, right? What did I miss? It’s still seeking common mode rejection.

View attachment 46412
under common mode feedback in the article I linked, this diagram clearly shows both that it is a balanced output and maybe raises the concern Irv is having? But this is addressable in the design of the amps, and as noted, many balanced output amplifiers exist.
I did not say you missed anything or wrong, just pointed out the fact that, as Wiki stated and I quoted in my post#48. I supposed I could have used clearer wording by saying it is better not to referred to (instead of "considered" push-pull as single ended, in order not to confused it with the single ended amps are not are not of the push-pull type, i.e. the same output device, or groups of output devices take care of the full cycle.

To me, this is more about terminologies than substance. I think we can all agree with Irv's point that at the end the load is just a speaker, so differential, balanced, or whatever you want to call it, really makes no difference. If Polk Audio says it does, then there must be something I missed, would love to know what it is.

By the way, the SDAs are passive speakers right? Just in case, if they are active, then I suppose differential vs unbalance single ended could make a difference.
 
Irvrobinson

Irvrobinson

Audioholic Spartan
@Irvrobinson Gene asked me to share this with you if you still don’t believe that balanced differential output amplifiers exist. But im pretty sure you already own the ATI version which was a better amp yet. Both are discussed in technical detail in the article I linked.

I know about the XPR-1, of course. Also, that was one of Gene's better reviews, which we all miss. I currently use an ATI AT3000 amplifier, which is dual-differential from input to output, as opposed to the follow-on generation AT6000, which is single differential at the input stages and dual differential in the output stages. Neither one seems to use a floating ground, as the output offset voltage is so low. As we once discussed with the McIntosh "quad balanced" amplifiers, I'm not sure all these multiple levels of differential circuitry really sounds so much better compared to more typical Class AB designs, but it certainly makes better advertising copy and, sometimes, better measurements.
 
S

shadyJ

Speaker of the House
Now we're in complete agreement. The rest is just semantics.
I am glad you guys could resolve your dispute in a civilized way, which is very much unlike how Matthew and I settled our disagreements. It always escalated into physical violence between Matthew and myself. In those clashes, I was always partial to clubbing weapons whereas Matthew was prone to stabbing and cutting weapons. I suppose our choice of weapons was not just an expression of personality but also symbolic of our philosophical differences. You might ask who won? Well, Matthew did flee to Florida, so I would take that for a kind of answer.
 
Irvrobinson

Irvrobinson

Audioholic Spartan
I am glad you guys could resolve your dispute in a civilized way, which is very much unlike how Matthew and I settled our disagreements. It always escalated into physical violence between Matthew and myself. In those clashes, I was always partial to clubbing weapons whereas Matthew was prone to stabbing and cutting weapons. I suppose our choice of weapons was not just an expression of personality but also symbolic of our philosophical differences. You might ask who won? Well, Matthew did flee to Florida, so I would take that for a kind of answer.
James, your sense of humor needs a tune-up, but you do great subwoofer reviews.
 

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