[Spad]

Quote:

Originally Posted by AdamWill I just read this thread, and there's one thing in the initial post I still can't shake off. I still can't figure out why this system requires one speaker to be labelled Left, and one to be labelled Right. If they each output a negative image of the other, why does it matter which one is left and which is right?

Polk's SDA is actually a lot more complicated that this thread might lead one to believe. Nspindel wasn't trying to do more than give a very general overview, which he did quite well actually.

As best I recall, this is how the process was explained to me many years ago:

In the Polk SDA SRSs the actual SDA section, not counting the considerable electronics involved, consists of two vertically aligned rows of four 6.5-inch mid-range drivers each. Between these is a row of four vertically aligned 2.5-inch tweeters. The innermost row is fed the inverted 100 to 1000 Hertz signal from the other via the connecting cable. This is why the speakers are designated left and right. Obviously this alone isn't sufficient to account for the system's effects, but--at least so far as I know--Dr. Polk kept the electronics (which fill an entire amp-sized bay) pretty close to the vest.

The speaker systems are 64-inches tall and weigh 155 pounds each. Polk recommends setting them up with at least 5.5-feet of free space to the outside of each speaker and that the distance between the speakers and the listening position form an equilateral triangle. They come with spikes sufficient to reach most sub-floors along with an 18-inch metal rod called a "bass brace." This screws into the back of the speakers about four feet above the floor and attaches to a wall stud.

The cabinets are 22-inches wide, so if you want to sit 10 feet from them the ideal setup would require that they be placed along a 25-foot wall--something not easily found in most homes. This is what we mean by hard to place, and that they tend to dominate a room. In reality, anything even close to the recommended setup gives pretty amazing results. In the article I mention above, the reviewers were able to separate them by a mere 5-feet. I currently have them about 8-feet apart and sit 10- to 12-feet from them and they sound terrific.

Their performance is even more dependent on program material that most systems. A mono source or one having very little channel separation renders the SDA effect useless. OTOH, well recorded material can be, and often is, astounding. Close your eyes and the speakers seem to disappear and along with them the walls. A symphony orchestra isn't simply created between the speakers as with most other systems. It arcs across the front, including the aforementioned free space, extends well beyond the back wall and curves down the side walls towards the listener.

Sounds like load of horsedoody, doesn't it? All I can say is read the reviews of the Polk SDA SRS (not simply SDA) by the most reputable audio writers of the time. And this is the key phrase to remember: "of the time." Today even a modest 5.1 system--including some made by Polk--can equal or better it's spatial performance. The magic was that all this was done by a legendary pair of speakers, not the bevy that many of us use today.

Sorry to be so windy.

 

[Spad]

Ooops. Sorry, Nspindel. I posted that ramble above without checking the thread between the time I began it and the time I posted.

 

[nspindel]

Like I said, you really want to hear Spad's, not mine. Mine are toys compared to his.

How about chaning the national meet to Vegas?!?!?! Works for me!

 

[nspindel]

Quote:

Originally Posted by Spad Ooops. Sorry, Nspindel. I posted that ramble above without checking the thread between the time I began it and the time I posted.

Some nerve....

 

[dohcmark8]

You can check out the Stereophile SDA review here: http://www.polksda.com/srsreview.shtml

Thanks to okiepolkie from ClubPolk for providing me with the link.

 

[nspindel]

Those are the ones! Thanks for finding that link! God those things are huge. In my next house I'm going to build a room just right for those speakers and go out and find myself a pair (and a killer amp...).

"At 100Hz the amplifier clipped at 1,650 watts into 6 ohms...." If I remember my physics, E=I x R and P=I x E. So P=I^2 x R. 1650 = I^2 x 6, so I = sqrt(1650/6) = 28.7amps???? Am I missing something, or can these speakers really draw ~30 amps??? Call the electrician, it's time to rewire the house.


Spad, there were two SRS models, one was bigger than the other. I think the smaller had 6 of the mid-drivers, the bigger had 8. I suppose just to make me feel really jealous you've got the 8, right???

 

[Spad]

Quote:

Originally Posted by dohcmark8 You can check out the Stereophile SDA review here: http://www.polksda.com/srsreview.shtml Thanks to ohiepolkie from ClubPolk for providing me with the link.

Hey, that's great man! I had no idea this stuff was available. Think you can bird dog another one?

There was another article from this period that I alluded to earlier in this thread about the SRS being chosen for a no-holds-barred, ultimate system. The magazine that ran it did a similar piece once a year or so. It was almost certainly in one of the big three audio mags of the era, namely Stereo Review, High Fidelity or Audio. I'm pretty sure it was SR, but I can't be sure since I practically devoured every audio periodical available during that period.

Thanks again for the link!

 

[dohcmark8]

Quote:

Originally Posted by Spad Hey, that's great man! I had no idea this stuff was available. Think you can bird dog another one? There was another article from this period that I alluded to earlier in this thread about the SRS being chosen for a no-holds-barred, ultimate system. The magazine that ran it did a similar piece once a year or so. It was almost certainly in one of the big three audio mags of the era, namely Stereo Review, High Fidelity or Audio. I'm pretty sure it was SR, but I can't be sure since I practically devoured every audio periodical available during that period. Thanks again for the link!

I did some Googling and it looks as if it was Stereo Review who choose it for an ultimate system. Unfortunately, I cant find any more info than that.

So instead of 2 birds with one stone, I have 2 stones and one bird...

 

[adhoc]

a most excellent thread! thanks nspindel and Tyll for raising this topic and that superb explanation respectively.

I'm sure many members here are wondering what the SDA SRSs' look like - well for the terminally lazy, here's a picture:

he's resting on the SDA SRS. the picture on the wall also shows dr matthew polk standing next to them. those are some huge speakers!!!

 

[nspindel]

Yeah, that picture on the wall is the one I was referring to in an earlier post. Nice one!

 

[Heiney9]

Ok I’m jumping into the fray here. I used to sell SDA’s back when they were new I’m also a contributing member of the Polk Audio forum and have heard almost every SDA speaker and even owned a pair (borrowed) from the store I worked at.

Very simply the idea is to cancel interaural crosstalk. Conventional line source speakers have a radiating pattern in which sounds from the right speaker reaches the LEFT ear at a different time interval than the right ear and vice-versa. This is regardless of reflected signals which will always be an issue. What SDA does is allow the sounds from each speaker to reach each ear at the same time by feeding a low level inverted signal to the SDA drivers in each cabinet. This helps the signals from each channel to reach each ear at the same time (theoretically). I say theoretically because reflected sound is always going to be present and there are certain phase shift elements that the crossover has to try to compensate for. The obvious interference is the width of our head which separates our ears. Hence the headphone analogy.

See this link for a review of the original SDA-SRS and a very good explanation of how they work and how well they sound.

http://www.polksda.com/srsreview.shtml

The reason they aren’t made anymore is has to do with the shear size and weight of the speaker as well as a market shift to HT type speakers which are smaller and easier to integrate into one’s system. I know several people who use SDA’s in a home theater set-up and they are great for that application as well.

A few years ago Polk introduced and manufactured a HT version of SDA technology called the SRT (Signature Reference Theater)

http://www.polkaudio.com/homeaudio/products/srtsystem/

To the naysayers or those who feel SDA is a gimmick or a trick you really don’t know what you are talking about. There were 4 or 5 generations of SDA products each one getting more and more finely tuned as time and research went on. The SRS (Signature Reference Series) were always the best of the best. These speakers may not appeal to everyone as they do sound different than most convention loudspeakers. But those of you who have never listened to a pair certainly can’t comment. If you don’t understand the design goal you shouldn’t be commenting either.

These are no different then bi-polar, omni-polar, sub/sat, line array, or any other design. They are another way of trying to make the sound as life-like as possible. I don’t really care for bi-polar speakers, does that mean I think they are a gimmick or a trick….no. It means I’ve listened to them and prefer a more conventional line source speaker. They certainly have some advantages, but personally they have a few more disadvantages so I choose not to own them. I don’t write them off as insignificant. For those of you who really want to understand these speakers and why they have a great following I invite you to look at www.polkaudio.com and click on the forums area and do a search. For those of you who dismiss the SDA and haven’t heard them or don’t understand the design I say….keep the drivel to yourself. How can you form an opinion if you’ve had no experience? It’s not opinion then…it could be taken as arrogance.

EDIT: I see someone already posted the link...didn't realize there was 3rd page

 

[BobMcG]

+1 and well done.

Thanks for saving me the time.

 

[pjoseph]

Hi folks,
One of the Polk Forum regular contributors asked me to chime in here. I am Paul DiComo, the geezer leaning up against the SDA - SRS in the photo above, Polk's Propaganda Minister and long term (22 years) Polk team member.

First, thank you to all of you who added to the conversation here, especially those with personal first-hand experience, which in my book trumps theory every time. What is it about human nature that makes people feel if they can critique something they have imperfect knowledge of and no experience with? I will not comment on Headroom's crossfeed technology because I have not heard it. As much as I believe that the SDA technology is valuable and valid, I would not jump to any conclusions about crossfeed even though it seems to be diametrically opposed to the SDA theory. One of the many things I have learned in my 30+ years in the audio community is that there are many ways to skin cats. Ideologues would have you believe that there is only one true path to audio Nirvana and IMHO that just ain't so. Besides, we are talking about one technology for speakers and one for headphones - two very different environments with very different sets of issues.

But enough pontification; the only real value I can add here is to attach a link to a white paper written by Matthew Polk on the latest iteration of SDA technology – SDA Surround. In it there is a very complete explanation of the theory and implementation of the original SDA technology as well as the new wrinkle.

SDA Surround White Paper

 

[Tyll Hertsens]

Quote:

Originally Posted by pjoseph Hi folks

First, a big thanks for chiming in here. Even though I disagree with the principles involved, I do appreciate you contribution and hope you'll feel welcome to continue to discuss this topic.

Quote:

Originally Posted by from the Polk SDA white paper For example, suppose we go to a concert and put a microphone at each of our ears to record exactly what we are hearing.

The biggest problem I have with this whole discussion centers around the fact that the above statement does not reflect how recordings are actually made. The above method is absolutely true for binaural recordings (those done with a dummy head) intended to be played back on headphones. In this case I do absolutely see that the Polk SDA system would do an excellent job of reproducing audio on speakers. But the fact remains that most recordings are not done with mikes at ears.

Typically the stereo image is created by the recording engineer panning or delaying the left/right channes in order to synthesize a left-right position in the soundstage. I believe I do clearly understand the Polk theory, but I think it is in error for the above reason.

How do you justify removing the cues heard from two speakers by using the Polk method when those cues are designed into the acoustic impression desired by the recording engineer.

As it regards synthesizing rear speakers in a surround system, it seems to me that the new Polk approach is reasonable well thought out and should provide a good synthesis of rear channels from a front speaker.

Quote:

What is it about human nature that makes people feel if they can critique something they have imperfect knowledge of and no experience with?

Science is a logical process and therefor can be meaningfully discussed in the abstract. But I agree that the final experience does trump all the argument. I have heard an SDA system only briefly at a trade show and would like to hear one well set up. Do you know anyone in the Boston-NY corridor that might invite me in for a listen?

 

[nspindel]

Paul, welcome to the thread, I'm so excited that you joined. I was hoping to attract some Polk expertise to this thread, so we could have an intelligent, non-bashing debate on this issue, especially with someone like Tyll on board. When I first started getting involved in serious headphone listening, it amazed me how completely diametrically opposed the notion of headphone crossfeed is to the Polk SDA way of thinking. Having been a long time Polk fan, I thought this would be a fascinating discussion.

I too would like to see a sort of mini-meet between the Polk camp and the HeadRoom folks. I live between Boston and New York, and own a pair of SDA's, though I'm sorely lacking power for them. I also don't have a showcase pair of SDA's - I own the 2's, but a good pair of SRS's powered by mono blocks going head-to-head (no pun intended) with high-end balanced cans off of a HeadRoom Max Balanced would be a clash of the Titans.

I'd be happy to host this gathering in April, or perhaps Polk might want to send someone with some killer SDA speakers/power to the head-fi meet in April. Boy would that be a killer part of the event..... And with Stereophile there to cover it (hopefully...), it'd be good press for everyone!

This is the kind of discussion that really keeps me interested in forums like this - good, honest debate on worthy scientific issues!!!!