Blog Forums DIY Speakers and Subwoofers Question for the experts: Cloning vintage speakers – Polk SRS?

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    • #23155
      don
      Participant

      Wife and I are fans of Polk SDA SRS speakers – we have been shopping around for a long while looking for the 1.2TL model without much luck. I see building my own (ala what Toid does all the time on his youtube channel) but for some reason, many of the members of the Polk Audio forum have the position that “they simply cannot be built” and the only success path is to locate and purchase originals.

      I really do not have a good understanding of that opinion – it appears very snobbish but I am wondering if there is something a bit deeper. I am a decent woodworker and can very easily recreate the cabinets. The crossover schematics are readily available and I was an electronics technician in the Navy for many years. Lots of folks hop up their crossovers with nicer and newer components, so that makes me think the electronics aspect is not the “why”. There are a couple of potential aspects such as specific speaker location and there are typically grooves cut into the inside of the cabinets to reduce some resonance effects.

      Anybody have any thoughts? I know there is a lot of science in speakers and that I do not know much of it compared to others, but following a proven formula should not be that difficult. Thanks for reading this, I am looking forward to the insights of others.

    • #23158
      123toid
      Keymaster

      @Don honestly I haven’t really looked into it. I started diving a little deeper today and at first glance it appears they are just four pair of horizontal MTM’s with a passive radiator. But once you dive deeper, it appears that is not the case at all. Each speaker uses 4 identical tweeters, 4 identical 6.5″ woofers and 4 identical 6.5″ sda woofers. It might actually be a three way (wired like a line array?). Here is another source that confirms the three different drivers along with the passive radiator. This definitely seems doable, but more information would be nice to have. If you are willing to do some more research, we can see what is possible.


    • #23160
      123toid
      Keymaster

      I had a few more minutes to spare and found a crossover diagram of the SDA SRS 1.2 TL


    • #23170
      123toid
      Keymaster

      While we are discussing it, here are the rest of the crossover designs for all the other models.


    • #23171
      don
      Participant

      Thank you for taking some time to look into this.

      These speakers are definitely a bit more complicated than the typical speaker. I had the pleasure of hearing some of them years ago and have wanted them ever since.

      It would appear that there are 8 mids, but like you said, peeling back each layer reveals more and more speaker science and this rabbit hole is deep. I am not giving up though…

    • #23173
      123toid
      Keymaster

      @Don honestly looking at the crossover diagram it doesn’t look that complicated. Just a second order the woofers. Seems they two sets of pairs in series and parallel. So the wiring seems easy enough. I am a little interested on why they choose two different woofers in the same build. I’ll have to look more into that. The more I look, the more I think something like this is definitely doable.


    • #23174
      don
      Participant

      I am not certain if the second set (of 4) midrange speakers is second order or not, but they are intended to help distinguish left from right from the listening position (they call it elimination of interaural crosstalk). It is very interesting that Polk designed such a thing into their speakers. They also designed it so that the tweeters are a point source of sound that “grows” with volume and frequency (the third tweeter down builds in first, followed by the fourth, then second, and first).

      Its all amazing stuff and it is a great listening experience, which is why I have wanted them. I believe that the Polk engineers know some stuff that the people on their forums do not know or understand, which is why there is such a “cannot build it yourself” mentality.

      I am in agreement with you, its a very doable project. Gotta track down a few more parts and hope to start sometime in the summer. Will post pics when I get there, in the meantime I hope you give the subject some attention on YouTube – I would like to see if some other DIYers would also be willing to jump in!

      Thanks again!

    • #23177
      elliottdesigns
      Participant

      Its very likely that the internals were shaped to reduce cabinet resonances, but it may also have been done to reduce even harmonics being re-emitted through the drivers. The only way I can see it truly working is with the original drivers, I presume you were able to get your hands on these? Other than that, it’s not a speaker configuration I’m familiar with, it’s definitely not a line array, not a proper one at least, and it probably has some bad comb filtering effects, but it certainly seems like a very interesting challenge. If you have any engineering (science) related questions, don’t hesitate to ask. I think there’s a few of us here.

    • #23188
      tvor-ceasar
      Moderator

      While we’re at it, here’s a couple more to help clear up (or confuse?) the questions you most definitely have, or will have.
      https://polksda.com/pdfs/SRSTLBrochure1990.pdf
      https://polksda.com/pdfs/SDASRS1-2.pdf
      https://audiokarma.org/forums/index.php?threads/polk-sda-srs-1-2tl-initial-impressions.243862/
      (hey, I go where there’s useful info so I can share with you all)


    • #23221
      don
      Participant

      I appreciate the replies and links. I also caught part of the livestream last night and the discussion about encouragement vice discouraging projects was very good.

      Answers to a couple of questions:

      I have acquired a majority of tweeters and mids (woofers?) needed for this project. I still need the passive radiators, the Polks are discontinued and are supposedly hard to come by.

      the reason for the different model drivers (midrange or woofers, whatever they are) is supposedly part of the design – the effect of cancelling out some sound from the opposite speaker. In my mind, I have simplified it into “they do a different job”.

      My timeline for this project is lengthy. Wife and I moved south last year and the sale of our home closes on Monday. We intend to build our forever home in our current area, so it may be a while before I am settled enough to build these beasts. As a benefit of the potentially long wait, I can continue to scour Ebay and Craigslist for parts. If I cannot get the parts I want, I have a line on equivalent replacements – with the exception of the passive radiators (need some help with those).

      My goal with these speakers is a little different than most folks have – wife and I want a home theater that can recreate a concert experience (we saw Iron Maiden as part of our 20th anniversary celebration, so THAT kind of concert) but we also want to enjoy the movie experience (Star Wars junkies, amongst other things). Since we are going to build our forever home, we will be able to dedicate some space.

      Thanks again to those that have responded, we really appreciate it.

    • #23222
      tvor-ceasar
      Moderator

      Glad you got the drivers. I see that Midwest Speaker Repair has the 6-1/2’s (both types) and the tweeters will be in soon. That Passive Radiator is a tough beast to find. If you had the basket, SimplySpeakers has a repair kit (just the radiator and surround) that looks like it “might work”. All other flat radiators I saw were 8″ or less, but I may not have looked hard enough. 🙁 Still need to figure out what you need to do to get the tuning.

      And with some of the other PDF’s, you have the outside dimensions and also the crossover.

      From what I see with that interconnect, you are getting a sort of Hafler surround effect.

      Oh, BTW, the resettable fuse in line with the tweeter array has a direct replacement available from Mouser.

      Don’t forget to mirror the speakers.

      I’d say you are well on your way with the exception of the PR. This should be an epic build when finished.


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