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Polk Legend L800 Tower Measurements

sweetchaos

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Polk Legend L800 Tower is US$6000/pair:
https://www.polkaudio.com/en-us/product/floor-standing-towers/l800
1617740286338.png

Audioholics posted a review today:
https://www.audioholics.com/tower-speaker-reviews/polk-legend-l800

Measurements:
NOTE: This is not full spinorama, as explained by Erin in post #3.
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Horizontal Directivity:
1617740131598.png


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Matthew Poes's video review was 6 months ago:

Discuss!
 
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Sancus

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Directivity seems pretty janky from 1-5K for the price point, definitely not up to Revel standards. Tweeter beaming is ugly too.

It also doesn't really seem to have unusually wide dispersion or anything, so I guess I don't really understand what they're trying to accomplish with the duplication of the midrange and tweeter.
 

hardisj

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It's not full spinorama data. Matthew states the following:
Due to the size of the speaker and size of the room I had to measure within, I was only able to measure out to 60 degrees on the horizontal axis. My results were shared with Polk’s engineers and Polks own internal measurements were shared back with me. Results were found to have a very high degree of agreement.


So, it is missing vertical data entirely and only out to 60 degrees horizontally. I'm not knocking the effort (god knows getting full spin data of such a speaker is a huge PITA). But the thread should be edited, IMHO, to keep from throwing anyone off. It is a limited data set with only +/- 60 degree data. The graphic really should make note of this as well as the all the data isn't actually there to build the spin data (thus, the listening window, early reflections, and DI data sets are not correct per actual "SPIN" requirements) and this could paint a much more flattering picture of this speaker.
 

Haint

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Matt seems to have really liked the SDA tech. Is there anything (technologically) preventing them from removing the two 10" woofers and just selling the quasi-dipole bookshelf section as a stand mount so it doesn't cost $6000 and weight 300lbs?
 

MrPeabody

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Very interesting speaker.

The concern with having two tweeters (and two midranges) side-by-side is that, for laterally off-axis listening positions where the difference in the two distances (distance to one tweeter minus the distance to the other tweeter) is in the same ballpark as the wavelength, comb filtering should be evident, due to the alternating cancellation and reinforcement of the two sources, as wavelength increases (or decreases). The frequency region where this would be most visible would start with wavelength slightly shorter than the horizontal spacing of the two tweeters (also the two midrange drivers) and continue upwards from there until the directivity of the tweeter is such that you have two lobes that don't overlap. And of course the further off-axis you are, the more pronounced it will be.

Given that the two midranges are directed outward and that they become fairly directional by the time you reach the crossover frequency, it is not surprising that you don't see this effect with them. The region where I would most expect to see this effect is in the mid-treble and fairly far off-axis horizontally. You do in fact see some of this effect in the Ronald McDonald directivity graph, from about 3 kHz on up to about 10 kHz. In this graph, you clearly see response peaks at about 4.3 kHz, 5.7 kHz, and 7.4 kHz, with nulls in between. Oddly, though, the ripple effect is nearly as strong on-axis or very slightly off-axis as it is very far off-axis. You should be able to get at least +/- 10 degrees horizontally off axis before you see any of this effect at all. Moreover, the difference in the two distances changes as the off-axis angle changes, especially when you are just far enough off-axis for the effect to begin. As such, the frequency for a peak or for a null in the ripple should change as you move further off-axis, which means that those lines should be curved such that the graph would resemble the sketch of a Christmas tree laying on its side, and not look nearly as ruler-straight as they are. The only explanation I think of is that the angled baffle is doing this, but I don't think this is a good explanation, because I still don't think the lines you see there should be ruler-straight.

The first two graphs indicate that the on-axis response is exceptionally flat, except for what is going on in the upper bass and lower midrange. Up around 5 kHz you do see a swing in the response at 20 degrees off axis, an up-and-down with a difference of 3 dB to 4 dB. This would likely produce some slight coloration for someone sitting 10 or more degrees off axis, but it would be slight and possibly not distracting. The most surprising thing I see is the strong directivity at high frequency. I would have thought that the two tweeters being aimed as they are would have yielded a broader dispersion pattern, but evidently not. The tweeters themselves must have unusually strong directivity throughout their response range. I expect that this is an attribute of this type of tweeter generally, ring radiators without the center dome.

As for that little messy area in the upper bass and lower midrange, this is most likely caused by the protrusion of the baffle just above the upper woofer. That messy business in the upper bass and lower midrange isn't especially bad, but it is probably audible and it is probably the biggest drawback of the design approach.

Which brings the question of whether the SDA actually works. I suspect that if it works, it will rely on early reflections from the side wall. The reflection from the right side wall, for example, would be heard strongly from the right ear and not the left, and since the driver that is aimed mostly at the right side wall emits the inverted left-channel signal, the effect would be to cancel much of the left-channel signal that the right ear hears. What concerns me, though, is that in order for this cancellation effect to work, the left-channel signal arriving via right-side-wall reflection needs to be out-of-phase with the primary left-channel signal coming directly from the left speaker. As such, it seems to me that in order for it to work as it is expected to work, the positioning of the speakers would have to be very particularly coordinated with the width of the room, and you would need to be sitting in the sweet spot. If you don't get this just right, then to me it seems like you could end up with an effect that isn't anything like the intended effect.

It would certainly be a fun speaker to play with on rainy days. But for me personally, it seems like you're paying a whole lot of money for something that isn't necessarily much more than a gimmick. When you're as old as I am, you've seen a lot of gimmicks come and go over the years.
 

MrPeabody

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Matt seems to have really liked the SDA tech. Is there anything (technologically) preventing them from removing the two 10" woofers and just selling the quasi-dipole bookshelf section as a stand mount so it doesn't cost $6000 and weight 300lbs?

Interesting thought. Surely the answer is "no", and doing that would make it much easier to position the speakers where the effect actually works the way it is supposed to. Also, the woofers won't have that reflector thingamaboob sticking out and causing that messy stuff in the upper bass and lower midrange. I'd much rather have it that way. In fact, another way it could have been done is as a tall stand-mount speaker, tall enough to run the angled baffle further down so that two smallish woofers could fit one beside the other just like the midrange and tweeter. This would permit better subwoofer integration and would still permit the speakers to be placed right where they need to be placed. But even with that, I still think that you probably need to be sitting at the center of the sweet spot in order for the effect to work as intended.
 

MZKM

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It also doesn't really seem to have unusually wide dispersion or anything, so I guess I don't really understand what they're trying to accomplish with the duplication of the midrange and tweeter.
It’s for their crosstalk cancellation. You run a wire between the two towers, it then uses that data and does something with it (inverted phase?) such that your right ear doesn’t hear the direct sound of the left tower and your left ear doesn’t hear the direct sound of the right ear. If you don’t have the wire connected, only one tweeter and mid play.

I guess it’s supposed to sound like you are wearing headphones, but with room interactions and bass impact. Not sure.
 
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MrPeabody

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It’s for their crosstalk cancellation. You run a wire between the two towers, it then uses that data and does something with it (inverted phase?) such that your right ear doesn’t hear the direct sound of the left tower and your left ear doesn’t hear the direct sound of the right ear. If you don’t have the wire connected, only one tweeter and mid play.

I guess it’s supposed to sound like you are wearing headphones, but with room interactions and bass impact. Not sure.

I think that all it is is running a pair from each speaker to the other speaker, connecting the outer driver pair of each speaker parallel to the inner driver pair of the other speaker but with opposite polarity. Ie., outside right = - inside left, and outside left = - inside right.
 

richard12511

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Directivity seems pretty janky from 1-5K for the price point, definitely not up to Revel standards. Tweeter beaming is ugly too.

It also doesn't really seem to have unusually wide dispersion or anything, so I guess I don't really understand what they're trying to accomplish with the duplication of the midrange and tweeter.

I think the directivity might be somewhat janky on purpose, based on the interviews I've seen. I think they're going for a really weird soundstage with the multiple side firing tweeters/mids. The reviews I've read/seen lead me to believe they succeeded. Most reviews seem to say it's good for a second system, just because of how different it sounds, but they wouldn't want it for their main system. One review did say it was the best he's ever heard, so he seemed to like the janky soundstage.
 

MakeMineVinyl

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Which brings the question of whether the SDA actually works. I suspect that if it works, it will rely on early reflections from the side wall.

In my own experiences I've found that to get the best soundstage which exists on the recording, each ear should hear only the speaker on that ear's side as much as practical. To get an expansive soundstage which does not necessarily reflect the recording's inherent soundstage, a speaker needs to have as wide and smooth a dispersion as possible, so a significant amount of sound comes from the room as much as the speaker itself.

These are two different takes on 'soundstage' - the one which is strictly on the recording, verses the one which is expansive, but heavily influenced by the room. Of course there is some overlap between these extremes.....

I prefer the former, which is best realized by highly directional speakers such as horns (as in my case horns which go from 100Hz up to inaudibility), or systems such as SDA used by Polk in conjunction with a room which is not overly live. The native soundstage in recordings varies wildly, but in the best of them, the sound comes from all directions; forward beyond the front wall, beyond the left/right boundaries of the speakers, and around the listener to the point where one would think that surround speakers are in use.

In systems and rooms which rely more on wide dispersion from the speakers interacting with the room, the soundstage can be similarly enveloping, but is more diffuse generally, with less specific imaging.

Highly directional speakers generally have a narrower 'sweet spot', while speakers which have wider dispersion have a more broad one. I would assume the Polk would be more like the former.

Listening to good examples of both approaches is a good thing.
 
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Matias

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Hmmm :rolleyes:

THE ONLY TRUE STEREO SPEAKER
Polk SDA speakers were the first true stereo speakers because they were able to maintain stereo separation all the way from the source to your ears. By acoustically isolating the two stereo channels, each ear hears only the correct stereo channel. The left ear hears left channel, and the right ear hears right channel. Recordings literally come alive in your listening room. Musical images are reproduced with clarity and pinpoint accuracy. You are immersed in an awe-inspiring three-dimensional sound stage that extends from wall-to-wall (width), floor to ceiling (height) and extends both in-front and behind the speakers (depth).
 
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MakeMineVinyl

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Hmmm :rolleyes:

THE ONLY TRUE STEREO SPEAKER
Polk SDA speakers were the first true stereo speakers because they were able to maintain stereo separation all the way from the source to your ears. By acoustically isolating the two stereo channels, each ear hears only the correct stereo channel. The left ear hears left channel, and the right ear hears right channel. Recordings literally come alive in your listening room. Musical images are reproduced with clarity and pinpoint accuracy. You are immersed in an awe-inspiring three-dimensional sound stage that extends from wall-to-wall (width), floor to ceiling (height) and extends both in-front and behind the speakers (depth).
I agree with the imaging ability when there is little cross contamination between the left and right speakers, but their marketing blub is a bit ripe.
 

MrPeabody

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richard12511

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I just don't see any way that this speaker can do what it is supposed to do without a lot of help from the sidewalls. When the sidewalls are out of the picture, I just don't see it.

Could it be that the inward firing sets cancel each other?, while the outer facing sets are far enough off axis from the opposite side ear? No idea if my question even makes sense.
 

MrPeabody

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Hmmm :rolleyes:

THE ONLY TRUE STEREO SPEAKER
Polk SDA speakers were the first true stereo speakers because they were able to maintain stereo separation all the way from the source to your ears. By acoustically isolating the two stereo channels, each ear hears only the correct stereo channel. The left ear hears left channel, and the right ear hears right channel. Recordings literally come alive in your listening room. Musical images are reproduced with clarity and pinpoint accuracy. You are immersed in an awe-inspiring three-dimensional sound stage that extends from wall-to-wall (width), floor to ceiling (height) and extends both in-front and behind the speakers (depth).

Is this some marketing spiel that you copied and pasted, or is it a strong assertion of your own? I tend to be skeptical of a great many things that are claimed in audio because over the years I've seen too much stuff that wasn't much more than a marketing gimmick. As I look at this, the sense that I get is that for anyone far enough from the speakers to be in the "far field", where the wavefronts from the individual drivers in each speaker have thoroughly combined into a single wavefront (for each speaker of course), the right ear is mainly going to heat R -L from the right speaker and L -R from the left speaker. The left ear will hear the same, R -L from the right speaker and L -R from the left speaker. I'm confident that this will be the case for the lower midrange, because for the lower midrange, the wavefronts emitted from the two midrange drivers (in one of the speakers) will thoroughly blend just the same as without the angled baffle and without the horizontal spacing of the drivers, assuming the listener is more than a meter or so from the speaker. For frequencies in the upper part of the midrange and covered by the tweeter it will be somewhat different because of the apparently strong directivity of this dome-less tweeter and the fairly strong directivity of the midrange driver at the upper reach of its range. For these frequencies the forward main lobes of the sound emitted from each side of the divided baffle will still overlap for a listening position directly in front of the speaker, but off to one side of the speaker, one side of the divided baffle will be stronger than the other. Consequently, the effect that you get is certain to depend very greatly on exactly where you are sitting. I do not doubt that if you sit close enough to the speaker and position them the appropriate distance apart from each other and angle them toward you, you will get the same effect that the design is meant to produce. But there just isn't any way that there can be any control of the effect experienced by a listener in a randomly chosen location more than a few feet from the speakers, because it is apparent that the effect will be different for different listeners in different locations. This is what it comes down to. The effect will be different for different listeners in different locations.
 

Matias

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This marketing text is in their website.
 

MrPeabody

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Could it be that the inward firing sets cancel each other?, while the outer facing sets are far enough off axis from the opposite side ear? No idea if my question even makes sense.

Each baffle is divided into an outward facing side and an inward facing side. The outward facing side emits the inverted signal for the inward facing side of the other channel. The idea is for cancellation to occur in a different way for each ear. For the right ear, the -L signal emitted from the outward facing side of the right speaker is supposed to cancel the +L signal from the inward facing side of the left speaker. For the left ear, the -R signal emitted from the outward facing side of the left speaker is supposed to cancel the +R signal from the inward facing side of the right speaker. The cancellation that is supposed to apply for the right ear is not supposed to apply for the left ear and vice versa. That is, even though the -L signal emitted from the outward facing side of the right speaker is supposed to cancel the +L signal from the inward facing side of the left speaker, for the right ear, this effect is not supposed to apply to what the left ear hears. And vice versa for the left ear. How is this supposed to happen? The angle in the baffle and the horizontal spacing of the drivers on the two halves of the divided baffle is supposed to make this happen. As I ponder this, it seems to me that this most likely works as intended if you are sitting very close to both speakers and the spacing between them is adequate and they are aimed appropriately, more or less directly toward you. If these conditions are met, I can see how it work, because then the sound that each ear hears will be different and adequately well controlled. But if these conditions are not met, I just don't see how it could work.
 

Kachda

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I listened to them during the NY audio show in 2020 and wasn’t particularly impressed.
I also asked them about the impact of cancellation when sitting off axis and they didn’t give me a convincing answer. The whole thing seemed like a gimmick
 
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