Getting the full SDA Effect from Polk L800 Speakers

Matthew J Poes

Matthew J Poes

Senior Audioholic
One other comment, is it just me, or has AH become a home for some reviewers with weird listening room set-ups? As with the Legacy Focus SE review, where the reviewer was also very positive about the speaker, the pictured in-room set-up is rather weird. Matthew's listening room is 25x11, the L800s are placed up against the front wall next to a projector screen, nearly in the corners, but on each side, very near the speaker, there's a thick room treatment panel that will have some unknown effects on how the speakers sound in the room.
that is also a false wall. They were actually 3 feet from the front wall. However Polk says they sound best up against a wall, not pulled out. The speakers actually work best in a position that normally is a huge compromise for most speakers. They work best up against a wall and very close together.
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
"Most amplifiers in general are single-ended output so finding a good amplifier that works is not a big problem."

Other than some weirdo Nelson Pass things, which solid state amplifiers do not have differential output stages? I don't think I've ever seen one, save some guitar amplifiers.
Your thinking of push pull. Push pull amplifiers are still single ended output. The pushing and pulling is tied together.

1617795267601.png


vs

1617795355447.jpeg
 
G

Golfx

Audioholic Intern
They work best in a weird set-up? Really? They wouldn't work for my room either, since the SDA cable is only 12 feet long, and my preferred speaker positions are a little more than 12 feet apart.

Caveats aside, this is the most positive review I've ever seen of a Polk speaker. If I get a chance I feel nearly compelled to listen to them.
It comes with two SDA cables which can be connected to total 24ft.
 
Irvrobinson

Irvrobinson

Audioholic Spartan
that is also a false wall. They were actually 3 feet from the front wall. However Polk says they sound best up against a wall, not pulled out. The speakers actually work best in a position that normally is a huge compromise for most speakers. They work best up against a wall and very close together.
Now that you mention the false wall, I think I can see that in your photo. How solid is the false wall? What is the construction of the side absorption panels?

Looking at the L800 owner's manual on Polk's web site, it does mention that the L800s should optimally placed against the front wall (which they call the back wall; whatever), and that the speaker to seating arrangement is optimally an isosceles triangle rather than the more typical equilateral triangle recommendation. Polk recommends a 6-8 feet separation between the speakers, which is narrower than typical, but I don't know if I'd describe it as "very close together". In retrospect, the 6-8 feet recommendation might actually be favorable for L/R placements these days in HT systems on the sides of large (75"+) active displays.
 
Kvn_Walker

Kvn_Walker

Audioholic General
Too bad they cost more then I can probably ever afford but impressive regardless!!! Probably outshine more expensive speakers then they are , engineering marvels .
Stop buying busted broken stuff off Craigslist and save... in a few years you might be able to score a pair for 3 or 4 grand. Never say never...
 
Irvrobinson

Irvrobinson

Audioholic Spartan
Your thinking of push pull. Push pull amplifiers are still single ended output. The pushing and pulling is tied together.

View attachment 46377

vs

View attachment 46378
The two diagrams at the end of your post are not of audio amplifiers per se, they are of op-amps (for the uninitiated, components or circuits sometimes used to construct audio amplifiers). All audio amplifiers meant to drive passive speakers have single-ended outputs by definition. Amplifiers with differential outputs in the audio world are pre-amps (or line-level components with XLR connectors). The purpose of using differential op-amps are to maintain the differential path from input to final amplifier output, so as to maximize CMRR.

Push-pull topology is not considered single-ended because it includes a phase-splitter. That's what the triangle with the +/- is in your first diagram. The two output devices operate in anti-phase. Audio amplifiers with a single-ended topology do not use phase-splitting.

I'm guessing your reference to ground comment must refer to the few amplifiers that use internal bridging and a floating ground.

I noted that single-ended amplifiers are not mentioned in the Polk owner's manual. How did you arrive at that conclusion? Did a Polk engineer tell you that?
 
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TLS Guy

TLS Guy

Audioholic Slumlord
I'm going to make the point that this SDA technology is bogus and can not be a contribution to realistic audio. In my view it is pure nonsense, and here is why.

I don't doubt it can produce an artificially wide soundstage by exaggerating left and right information.

Now in a concert hall a trumpet say on the right of the orchestra will be heard by both ears. We listen with left right crosstalk.

A flute say in the center will be heard equally by both ears. So let us focus on the center stage.

Now play this through an SDA speaker, and the flute should play equally in both speakers. Now let is play it through this SDA contraption, and an out of phase signal is now fed equally to both those speakers. This has to result in reduction of the central image at the expense of artificial enhancement of the left and right information.

There is no way that this can correctly balance a good recording of a symphony orchestra and choir.

I did hear the previous generation of SDA speakers and thought they were just plain awful, providing very unnatural reproduction.

I have not heard the new SDA efforts, but the whole premise makes absolutely no sense to me, and smacks of extreme gimmickry.

The real villains here though, are recording engineers that do not know their craft. I'm talking about peppering a multitude of microphones all over the place, where two, or at the most three would be a huge improvement.

This has been really brought home to me of late. The BBC have on iPlayer the Easter service form King's College. The sound was outstanding, with everything in acoustic perspective. The sound stage way bigger than the room and the organ in the far distance.

No mics to be seen, except on one shot. To may surprise there were three large diaphragm Coles ribbon mics, spaced at a distance. Now these mics were originally manufactured by Standard Telephones and Cables back in the 1950s, and much loved by the BBC. After STD went out of business, these mics have been produced by Coles since.

The sound stage produced was absolutely incredible, and the organ reproduction most realistic, with a phenomenal bass response.

Producing a realistic soundstage is 50/50 microphone technique and speakers, and not nonsensical gimmicks like SDA.

Here is another example of the benefits of minimalist miking.

I have referred before to the Scott Brothers DUO. They have continued to entertain through this pandemic. Tom uses pure Blumlein intensity technique, with a single crossed pair at a distance.

This recent recording which is fantastic, comes from Ripon Cathedral.


This includes Jonathan's transcription of the Saint Saens organ symphony, where he plays the organ, piano and orchestral parts all by himself! He uses pedals and all four keyboards at once, using thumbs down.

This recording really can demonstrate how effective the Dolby upmixer is with a phase coherent recording. This organ has three widely spaced divisions. There are large divisions right ahead, on the left at the side is a large pedal division and some powerful reeds. On the right side is is division containing both flutes and reeds.

In my room this all sounds best in the third row. The main organ is the distant and the powerful pedal reads blasting hard left. The more delicate division from the right.

Fortunately my surrounds are potent, and only 12 db down at 25 Hz. Each surround speaker powered by 250 watts. The whole effect is incredibly realistic, and you are literally placed at the four manual console by Jonathan Scott.
 
T

Trebdp83

Audioholic Field Marshall
Can we get a clean up in the Polk L800 thread?! I nearly slipped and fell on all the sour grapes.:rolleyes:
 
S

shadyJ

Speaker of the House
I'm going to make the point that this SDA technology is bogus and can not be a contribution to realistic audio. In my view it is pure nonsense, and here is why.

I don't doubt it can produce an artificially wide soundstage by exaggerating left and right information.

Now in a concert hall a trumpet say on the right of the orchestra will be heard by both ears. We listen with left right crosstalk.

A flute say in the center will be heard equally by both ears. So let us focus on the center stage.

Now play this through an SDA speaker, and the flute should play equally in both speakers. Now let is play it through this SDA contraption, and an out of phase signal is now fed equally to both those speakers. This has to result in reduction of the central image at the expense of artificial enhancement of the left and right information.

There is no way that this can correctly balance a good recording of a symphony orchestra and choir.

I did hear the previous generation of SDA speakers and thought they were just plain awful, providing very unnatural reproduction.

I have not heard the new SDA efforts, but the whole premise makes absolutely no sense to me, and smacks of extreme gimmickry.
I don't know about previous SDA speakers, but the L800s don't exaggerate the left and right information. They just reduce the level of cross talk from the other speaker.

Yes, we do hear cross talk in real life, but it's actually exaggerated by traditional stereo speaker systems. Stereo imaging is just an illusion, after all, and stereo cross-talk is a flaw in maintaining that illusion. Reducing crosstalk only strengthens the illusion created by stereo sound.

Reducing cross-talk isn't some kind of special effect gimmick, at least insofar as the stereo illusion is not already a gimmick. SDA just filters out stuff that isn't in the recording from hitting your ears, i.e., the stuff in the left speaker isn't really meant for the right ear and vice-versa.

And no, the SDA effect does not come at the expense of central imaging. If you think that, you need to read up a bit more on what is occurring. Center imaging on these speakers is excellent, very pinpoint.

I don't think these speakers are perfect, since the effect only holds for a narrow area around the sweet spot. They are great for the kind of person who enjoys solitary listening, but if you want a system for a wide listening area with a bunch of people, this definitely isn't the speaker for that application.
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
Now that you mention the false wall, I think I can see that in your photo. How solid is the false wall? What is the construction of the side absorption panels?

Looking at the L800 owner's manual on Polk's web site, it does mention that the L800s should optimally placed against the front wall (which they call the back wall; whatever), and that the speaker to seating arrangement is optimally an isosceles triangle rather than the more typical equilateral triangle recommendation. Polk recommends a 6-8 feet separation between the speakers, which is narrower than typical, but I don't know if I'd describe it as "very close together". In retrospect, the 6-8 feet recommendation might actually be favorable for L/R placements these days in HT systems on the sides of large (75"+) active displays.
Yes exactly. It’s actually an optimal placement requirement for those who need to stick a speaker on either side of their tv against a wall.

the false wall is not heavily constructed. It’a 1x2 framing wrapped in fabric with a 2x4 support frame for the fabric panels to sit against.

how far apart they sit is dependent on how far back you listen. Their suggestion is based on a typical 8-12 foot listening distance. If you listen closer than 8 feet the they might be better closer. I had a lot of conversations with the designer about this.

the acoustic panels are a mix of blue jeans insulation and 8lb rockwool. The have an open frame made of 4x1 pine and some bracing and feet. The panel is open on both sides. When placed near a wall they would have the absorption of a 6” panel or so. The design places the denser material near the wall.
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
The two diagrams at the end of your post are not of audio amplifiers per se, they are of op-amps (for the uninitiated, components or circuits sometimes used to construct audio amplifiers). All audio amplifiers meant to drive passive speakers have single-ended outputs by definition. Amplifiers with differential outputs in the audio world are pre-amps (or line-level components with XLR connectors). The purpose of using differential op-amps are to maintain the differential path from input to final amplifier output, so as to maximize CMRR.

Push-pull topology is not considered single-ended because it includes a phase-splitter. That's what the triangle with the +/- is in your first diagram. The two output devices operate in anti-phase. Audio amplifiers with a single-ended topology do not use phase-splitting.

I'm guessing your reference to ground comment must refer to the few amplifiers that use internal bridging and a floating ground.

I noted that single-ended amplifiers are not mentioned in the Polk owner's manual. How did you arrive at that conclusion? Did a Polk engineer tell you that?
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.
 
Matthew J Poes

Matthew J Poes

Senior Audioholic
I'm going to make the point that this SDA technology is bogus and can not be a contribution to realistic audio. In my view it is pure nonsense, and here is why.

I don't doubt it can produce an artificially wide soundstage by exaggerating left and right information.

Now in a concert hall a trumpet say on the right of the orchestra will be heard by both ears. We listen with left right crosstalk.

A flute say in the center will be heard equally by both ears. So let us focus on the center stage.

Now play this through an SDA speaker, and the flute should play equally in both speakers. Now let is play it through this SDA contraption, and an out of phase signal is now fed equally to both those speakers. This has to result in reduction of the central image at the expense of artificial enhancement of the left and right information.

There is no way that this can correctly balance a good recording of a symphony orchestra and choir.

I did hear the previous generation of SDA speakers and thought they were just plain awful, providing very unnatural reproduction.

I have not heard the new SDA efforts, but the whole premise makes absolutely no sense to me, and smacks of extreme gimmickry.

The real villains here though, are recording engineers that do not know their craft. I'm talking about peppering a multitude of microphones all over the place, where two, or at the most three would be a huge improvement.

This has been really brought home to me of late. The BBC have on iPlayer the Easter service form King's College. The sound was outstanding, with everything in acoustic perspective. The sound stage way bigger than the room and the organ in the far distance.

No mics to be seen, except on one shot. To may surprise there were three large diaphragm Coles ribbon mics, spaced at a distance. Now these mics were originally manufactured by Standard Telephones and Cables back in the 1950s, and much loved by the BBC. After STD went out of business, these mics have been produced by Coles since.

The sound stage produced was absolutely incredible, and the organ reproduction most realistic, with a phenomenal bass response.

Producing a realistic soundstage is 50/50 microphone technique and speakers, and not nonsensical gimmicks like SDA.

Here is another example of the benefits of minimalist miking.

I have referred before to the Scott Brothers DUO. They have continued to entertain through this pandemic. Tom uses pure Blumlein intensity technique, with a single crossed pair at a distance.

This recent recording which is fantastic, comes from Ripon Cathedral.


This includes Jonathan's transcription of the Saint Saens organ symphony, where he plays the organ, piano and orchestral parts all by himself! He uses pedals and all four keyboards at once, using thumbs down.

This recording really can demonstrate how effective the Dolby upmixer is with a phase coherent recording. This organ has three widely spaced divisions. There are large divisions right ahead, on the left at the side is a large pedal division and some powerful reeds. On the right side is is division containing both flutes and reeds.

In my room this all sounds best in the third row. The main organ is the distant and the powerful pedal reads blasting hard left. The more delicate division from the right.

Fortunately my surrounds are potent, and only 12 db down at 25 Hz. Each surround speaker powered by 250 watts. The whole effect is incredibly realistic, and you are literally placed at the four manual console by Jonathan Scott.
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.
 
Irvrobinson

Irvrobinson

Audioholic Spartan
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.

Matthew, I said the outputs, the speaker terminals, of all amplifiers intended to drive passive loudspeakers are single-ended. How can they not be? There are only two connectors, a positive one and a negative one. There isn't any anti-phase information at the output terminals. All levels of differential, dual-differential, or bridging circuitry are by definition electrically re-combined before the current reaches the output terminals. This makes speaker connections single-ended. Don't believe me? Ask Gene. The use of differential output stages are electrically transparent to speakers.

Having not seen the circuit schematics for, well, nearly all power amplifiers, I can't speak to which ones have floating grounds and which are earthed grounds. I also don't know exactly how the SDA circuitry is configured, which of course is a unique problem for Polk speakers. I didn't realize until this conversation that many (most?) Class D amplifiers have floating grounds (meaning there's a voltage offset at the ground terminal), because I don't use Class D amplifiers (well, except for integrated amps in the SVS and Velodyne subwoofers), so I didn't care. A simple search though turned up this page for REL subwoofers:


So, the floating ground messes up their circuit strategy for the REL speaker-level subwoofer inputs, and can cause damage. How quaint. I didn't notice any such warnings for my Velodyne sub, either in the owner's manual or on the web site, but that doesn't mean the vulnerability doesn't exist. I do wonder, however, if the appearance of significant voltage at the negative terminal of an amplifier's speaker output is the issue that the Polk engineers are talking about. Perhaps that reduces the level of the cancellation signal? I don't know. Perhaps Polk could send you a comment or post themselves.

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.
Are you referring to this statement in the Q&A section of the DAC (Digital Amplifier Company) website:

Q: Can I connect my Subwoofer with the speaker level inputs?

A: It Depends. Maraschino amplifiers use what's known as a "Bridged Output Stage". This delivers clean, stable, high-current power to your speakers, but can not be used to drive some subwoofers with common-ground speaker level inputs. These share a connection to ground which would be damaging to your Maraschino equipment. Some subwoofers have facility for balanced power inputs. You can check this by using an ohm meter to measure resistance between the two negative terminals. As long as it has a very high resistance (something around 10Kohms or more) between the pair you'll be fine. Dual subwoofers with amplified but physically separate cabinets would be okay, too. As long as the amps can't see each other electrically, you should be fine. When in doubt, ask us!

This is the same ground-reference issue the REL site mentions. This has nothing to do with differential output stages, this has to do with DAC using a floating ground. The ATI AT3000 amplifier I use is essentially a bridged differential design internally, and now I wonder what grounding strategy it uses, not that it seems to matter to my speakers at all.

So I suspect that the real issue with the SDA circuitry is that it's incompatible with a floating ground amplifier. If so, it would be good to clarify and highlight this point.
 
STC

STC

Junior Audioholic
I'm going to make the point that this SDA technology is bogus and can not be a contribution to realistic audio. In my view it is pure nonsense, and here is why.

I don't doubt it can produce an artificially wide soundstage by exaggerating left and right information.

Now in a concert hall a trumpet say on the right of the orchestra will be heard by both ears. We listen with left right crosstalk.

A flute say in the center will be heard equally by both ears. So let us focus on the center stage.

Now play this through an SDA speaker, and the flute should play equally in both speakers. Now let is play it through this SDA contraption, and an out of phase signal is now fed equally to both those speakers. This has to result in reduction of the central image at the expense of artificial enhancement of the left and right information.

There is no way that this can correctly balance a good recording of a symphony orchestra and choir.

I did hear the previous generation of SDA speakers and thought they were just plain awful, providing very unnatural reproduction.

I have not heard the new SDA efforts, but the whole premise makes absolutely no sense to me, and smacks of extreme gimmickry.

The real villains here though, are recording engineers that do not know their craft. I'm talking about peppering a multitude of microphones all over the place, where two, or at the most three would be a huge improvement.

This has been really brought home to me of late. The BBC have on iPlayer the Easter service form King's College. The sound was outstanding, with everything in acoustic perspective. The sound stage way bigger than the room and the organ in the far distance.

No mics to be seen, except on one shot. To may surprise there were three large diaphragm Coles ribbon mics, spaced at a distance. Now these mics were originally manufactured by Standard Telephones and Cables back in the 1950s, and much loved by the BBC. After STD went out of business, these mics have been produced by Coles since.

The sound stage produced was absolutely incredible, and the organ reproduction most realistic, with a phenomenal bass response.

Producing a realistic soundstage is 50/50 microphone technique and speakers, and not nonsensical gimmicks like SDA.

Here is another example of the benefits of minimalist miking.

I have referred before to the Scott Brothers DUO. They have continued to entertain through this pandemic. Tom uses pure Blumlein intensity technique, with a single crossed pair at a distance.

This recent recording which is fantastic, comes from Ripon Cathedral.


This includes Jonathan's transcription of the Saint Saens organ symphony, where he plays the organ, piano and orchestral parts all by himself! He uses pedals and all four keyboards at once, using thumbs down.

This recording really can demonstrate how effective the Dolby upmixer is with a phase coherent recording. This organ has three widely spaced divisions. There are large divisions right ahead, on the left at the side is a large pedal division and some powerful reeds. On the right side is is division containing both flutes and reeds.

In my room this all sounds best in the third row. The main organ is the distant and the powerful pedal reads blasting hard left. The more delicate division from the right.

Fortunately my surrounds are potent, and only 12 db down at 25 Hz. Each surround speaker powered by 250 watts. The whole effect is incredibly realistic, and you are literally placed at the four manual console by Jonathan Scott.
I have been using crosstalk cancellation for more than 10 years and never heard anything that you are describing. I am not sure how the IACXT is employed by Polk and my guess is it is a one shot cancellation. It is possible that the smearing can happen with one shot cancellation but not as profound as you suggest. Ideally, the correct way to cancel is to do it recursively which anyone could do with a simple ping pong or flanger in DAW or one of the plugins. You can read all about crosstalk cancellation at the non profit organization - Ambiophonics Institute.
 
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Matthew J Poes

Matthew J Poes

Senior Audioholic
Matthew, I said the outputs, the speaker terminals, of all amplifiers intended to drive passive loudspeakers are single-ended. How can they not be? There are only two connectors, a positive one and a negative one. There isn't any anti-phase information at the output terminals. All levels of differential, dual-differential, or bridging circuitry are by definition electrically re-combined before the current reaches the output terminals. This makes speaker connections single-ended. Don't believe me? Ask Gene. The use of differential output stages are electrically transparent to speakers.

Having not seen the circuit schematics for, well, nearly all power amplifiers, I can't speak to which ones have floating grounds and which are earthed grounds. I also don't know exactly how the SDA circuitry is configured, which of course is a unique problem for Polk speakers. I didn't realize until this conversation that many (most?) Class D amplifiers have floating grounds (meaning there's a voltage offset at the ground terminal), because I don't use Class D amplifiers (well, except for integrated amps in the SVS and Velodyne subwoofers), so I didn't care. A simple search though turned up this page for REL subwoofers:


So, the floating ground messes up their circuit strategy for the REL speaker-level subwoofer inputs, and can cause damage. How quaint. I didn't notice any such warnings for my Velodyne sub, either in the owner's manual or on the web site, but that doesn't mean the vulnerability doesn't exist. I do wonder, however, if the appearance of significant voltage at the negative terminal of an amplifier's speaker output is the issue that the Polk engineers are talking about. Perhaps that reduces the level of the cancellation signal? I don't know. Perhaps Polk could send you a comment or post themselves.



Are you referring to this statement in the Q&A section of the DAC (Digital Amplifier Company) website:

Q: Can I connect my Subwoofer with the speaker level inputs?

A: It Depends. Maraschino amplifiers use what's known as a "Bridged Output Stage". This delivers clean, stable, high-current power to your speakers, but can not be used to drive some subwoofers with common-ground speaker level inputs. These share a connection to ground which would be damaging to your Maraschino equipment. Some subwoofers have facility for balanced power inputs. You can check this by using an ohm meter to measure resistance between the two negative terminals. As long as it has a very high resistance (something around 10Kohms or more) between the pair you'll be fine. Dual subwoofers with amplified but physically separate cabinets would be okay, too. As long as the amps can't see each other electrically, you should be fine. When in doubt, ask us!


This is the same ground-reference issue the REL site mentions. This has nothing to do with differential output stages, this has to do with DAC using a floating ground. The ATI AT3000 amplifier I use is essentially a bridged differential design internally, and now I wonder what grounding strategy it uses, not that it seems to matter to my speakers at all.

So I suspect that the real issue with the SDA circuitry is that it's incompatible with a floating ground amplifier. If so, it would be good to clarify and highlight this point.
You are still not correct. A differential output does not need a ground. There is anti phase information. Please read the article I linked to.
 
Irvrobinson

Irvrobinson

Audioholic Spartan
You are still not correct. A differential output does not need a ground. There is anti phase information. Please read the article I linked to.
There is anti-phase information in the speaker outputs of an amplifier with a differential output stage? You're on your own, Matthew.
 
P

PENG

Audioholic Slumlord
LOL didn't know purchases of speakers at particular price point came with review room expectations at all....from what I've seen of many reviewer's home rooms, meh in any case (or their subjective reviews, too). Fremer's is simply a mess, let alone his doofus reviews....Stereophile, TAS and the Analog Planet fans can have him.
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.
 

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