SDA passive radiator weight (metal cap)

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benjbroke
benjbroke Posts: 10
in Customer Service
Does anybody have (or knows where to get) the weight for SDA/SRS passive radiator?
I believe it can be found in SW120 and SW150, perhaps others. It looks as a metal cap glued to the styrofoam from the back. Any help would be highly appreciated. Thanks
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  • pitdogg2
    pitdogg2 Posts: 24,560
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    It always looked like a carriage bolt to me. Which passive?
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  • benjbroke
    benjbroke Posts: 10
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    SW150
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  • benjbroke
    benjbroke Posts: 10
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    nvgjdb17wu4t.jpeg
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  • pitdogg2
    pitdogg2 Posts: 24,560
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    That will be difficult. Those hardly EVER come up for sale. If it had been the 12" model I'd say look at eBay. I've seen one pair of the sw150 on ebay in 10yrs. They sold faster than I could hit buy!
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  • Toolfan66
    Toolfan66 Posts: 16,895
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    Why do you need one?

    The SW150's came with, and without them..

    It almost seems like the 2.3's, and 1.2's came without, and the 2.3TL's, and the 1.2TL's came with them. The SRS 2's might be the same way between Blade/Blade and Pin/Blade models.

    I am truly just guessing here, but I can tell you my 1.2's came without, and my 1.2TL's came with.

    And we all know Polk used old stock of parts as the speakers transitioned.
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  • benjbroke
    benjbroke Posts: 10
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    I have 1.2TL and one of them has it, another does not. This looks weird. I wonder whether one of previous owners could lose it or replaced a radiator. This extra weight should have some effect on higher frequencies and there may be a reason Polk added it. I don't need the radiator, just the weight itself
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  • pitdogg2
    pitdogg2 Posts: 24,560
    edited August 2022
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    Please post a picture of the passive that doesn't have the weight. Post a picture of the back where the weight would be.
    @Toolfan66 is correct in that some did some didn't.
    It almost seems like the 2.3's, and 1.2's came without, and the 2.3TL's, and the 1.2TL's came with them. The SRS 2's might be the same way between Blade/Blade and Pin/Blade models.
    In my experience in the SRS 2 blade/blade speaker some did have the weight as i bought a pair of passive radiators from a set both had weights.

    Polk had ways of making up the weight in more ways than just a bolt. Some had heavier front covers than other passives, IME those didn't have the bolt "weight"
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  • benjbroke
    benjbroke Posts: 10
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    Hi. Sorry for the delay (was on vacation). So, here're 2 photos - with and without the weigh. Also, I put both to the scales and they are 1375g vs. 1255g respectively. Thus, if we assume the chassis is the same (it looks the same to me), the weight itself should be 120g which is quite a lot. Opinions?621hvditj3ik.jpg
    melrlvkgil58.jpg
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  • nooshinjohn
    nooshinjohn Posts: 25,095
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    My suggest, and it is only that, is that the SW missing the weight never had one to start with. There is no evidence of glue on the foam. If you want to add one, remove the bolt from the one that have one and weigh it. Take that with you to a specialty shop and try matching it with something of the same type and weight and epoxy them back in place.
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  • pitdogg2
    pitdogg2 Posts: 24,560
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    Well we know it's a 120g difference. So the bolt and adhesive need to be pretty close. The rub is you muck it up and you're down a passive and out a set of speakers.
    Personally I'd leave well enough alone and put a watch/notification on ebay and bid aggressive on the pair that comes up. It may be 2 or more years.
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  • benjbroke
    benjbroke Posts: 10
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    Yep. There's no signs of glue but given the age of these speakers and how many hands they could change I'd not dismiss the possibility this radiator had been replaced at some point. Also, assuming Toolfan66 is right, it could be from the 1.2 rather than from 1.2TL. 1.2 has different crossover and drivers and that could result also in the lighter radiator. Based on my understanding, this weight should protect the radiator from relatively higher frequencies and probably result in a better bass articulation. So, I'd try to restore it back to what it was initially designed to be.
    I think I saw some posts with 12" radiators from SDA-1C with the same or very similar weight. I wonder if somebody here can have a damaged SDA-1C radiator to part or at least to check the weight of this thing. There're plenty of these 12" radiators available and the weight could be the same.
    I actually prefer not to try removing the weight from my radiator as if I damage it there's no way to find a substitute.
    Thoughts?
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  • pitdogg2
    pitdogg2 Posts: 24,560
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    1.2 and 1.2tl afaik used the same drivers, different tweeters that is the reason for the XO difference. I had thought the passives were the same between the two.
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  • Gardenstater
    Gardenstater Posts: 4,183
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    I checked a bolt weight calculator online and a 3/8" x 3/4" long carriage bolt (just a guess for an example) would weigh around 11.9 g. It is the moving mass that is what matters for determining the tuning frequency of a passive radiator. There could be lots of variation in the frame weight that could throw things off. As pitdogg2 so wisely stated, different PRs could have different weights of the cone cap.

    The higher the moving mass, the lower the tuning frequency for a given PR. Also, the larger the speaker enclosure the less moving mass needed for a given tuning frequency.
    George / NJ

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  • F1nut
    F1nut Posts: 49,795
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    Check the thickness of the foam disc on the front of the two PR's. Is one thicker than the other?
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  • benjbroke
    benjbroke Posts: 10
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    F1nut - how?
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  • F1nut
    F1nut Posts: 49,795
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    Should be obvious to the naked eye.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • benjbroke
    benjbroke Posts: 10
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    f1nut - do you mean to a naked X-Ray eye? :)
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  • F1nut
    F1nut Posts: 49,795
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    Clueless you are.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • benjbroke
    benjbroke Posts: 10
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    F1nut - sure, your Unapproachable Wisdomness. Your intelligence brings the blazing illumination upon us - the stupidest and miserable part of the society.
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  • F1nut
    F1nut Posts: 49,795
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    Like I said...clueless. Listed!
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • pitdogg2
    pitdogg2 Posts: 24,560
    edited September 2022
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    benjbroke wrote: »
    f1nut - do you mean to a naked X-Ray eye? :)

    Yes. Some had a foam like material, others had a hard plastic material that was much thinner.
    Some of the plastic material could also be different thickness.
    It is easily discernible.
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  • benjbroke
    benjbroke Posts: 10
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    both have hard plastic on the front and styrofoam inside and feel the same/similar thickness as per touch. Of course, only The Great & Genius F1nut can see them :)
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