SDA-2A, Any experience replacing the puckered membrane on the passive radiators?

Baker
Baker Posts: 18
in Vintage Speakers
I was able to remove the old material, and have fashioned some replacements of automotive upholstery.

The new burgundy inserts weigh a little more than the old membrane.

What will happen to my bass?
I was even thinking... maybe a quarter or a silver dollar in the center, under the upholstery might improve my bass?

I'm not beyond adding real 12" woofers...

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Answers

  • pitdogg2
    pitdogg2 Posts: 25,436
    OH BOY !!
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  • invalid
    invalid Posts: 1,365
    Not a good idea, leave them alone or try and find some used ones.
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  • Gardenstater
    Gardenstater Posts: 4,459
    You. Removed. It? This is not going to fare well, most likely. The weight and compliance are critical.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • aprazer402
    aprazer402 Posts: 3,147
    Your upholstery idea doesn't look right to me. You're free to do what you want. But the vast majority here will recommend repairing with the original parts. If your design doesn't work out, you should look on auction and sale sites for the exact replacements, which are the "SW-121" passive radiator. Welcome, many very smart people here willing to help. Audio enthusiasts can be persnickety. Use the search function and ask questions.
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  • Baker
    Baker Posts: 18
    Looks like I’m going down the wrong path.

    Thanks for that part number. I’ll start looking for some replacements.

    Not out anything, as they were in terrible condition.
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  • aprazer402
    aprazer402 Posts: 3,147
    The Polk SDA 2A's present an amplifier with a true 4 ohm or even lower load. Which requires an amplifier of sufficient wattage, preferably high current AND can accept 4-ohm speakers. These are not easy speakers to drive. Very few older receivers and most newer ones cannot accomplish this without damage to either the amplifier, the speakers or both if over-driven even modestly. An integrated or separate power and pre-amp would be recommended by most here.
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  • Toolfan66
    Toolfan66 Posts: 17,234
    edited April 2022
    I’m going to go against the grain here, only because you have removed the other material, and I am also very anal, so I wouldn’t want the bubbles in them either.

    At this point what do you have to lose? The only thing I would recommend is finding some other material (black as well) that may be a better match, hell maybe an upholstery shop would be willing to do the work? Maybe not cost effective on these.

    Anyway at least if it doesn’t work out you can play with these till you find something else, like you said they were in terrible condition, not like you can call up Polk for replacements..

    My vote is to go for it, but find some better material, maybe Joann’s has something…

    Have fun…
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  • Baker
    Baker Posts: 18
    Appreciate the kind comments, thank you.

    As for my amp set-up: Yamaha M-80/C-80
    Have the switch at the rear set to 4 ohms.

    Thanks for helping, to all!
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  • Baker
    Baker Posts: 18
    Quick note to Toolfan66:

    I also share your love of tools.
    35 years as Tool Maker
    Every major manufacturing joint in town...

    One must remember that manufacturing is not only quality driven, but so also by economics.

    Bet Polk had less than a nickel in those membranes...
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  • Gardenstater
    Gardenstater Posts: 4,459
    How did you separate the surround rubber from the membrane and the membrane from whatever is behind it (styrofoam)?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • F1nut
    F1nut Posts: 50,537
    The weight of the membrane, as you called it, is critical as it is used to tune the bass response.

    Never replace the PR's with active drivers, it simply will not work for many reasons.
    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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  • Baker
    Baker Posts: 18
    Little bit of heat, and it peeled off with ease.

    The surface below is very shiny and slick. A plastic material ~.020” thick. A poor surface for adhesion, thus the puckering problem.

    I don’t need to use the word membrane.
    Please share the actual term for this part.
    I would be pleased to know...
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  • Baker
    Baker Posts: 18
    Re: Driver in lieu of radiator

    That concept would require sealing off the upper portion of the cabinet. (to maintain the “airtight” condition around the mids and tweeter)

    The lower portion of the cabinet would then require porting.

    Just a theory, and was hoping for some brainstorming to occur here...

    Polk couldn’t get a driver in them, and hold the $599 sale price.
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  • F1nut
    F1nut Posts: 50,537
    Stop trying to reinvent the wheel of which you don't seem to even begin to understand.
    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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  • Baker
    Baker Posts: 18
    Ok, thanks for the help.
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  • txcoastal1
    txcoastal1 Posts: 13,281
    edited April 2022
    A passive radiator is more inline with a port than a driver...installing a driver especially that size will definitely s cr ew up the design and sound from the midwoofers

    You would need to completely redesign the cabinet and the entire crossover system
    2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
    Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
    Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
    Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC

    erat interfectorem cesar et **** dictatorem dicere a
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  • Clipdat
    Clipdat Posts: 12,934
    Baker wrote: »
    Polk couldn’t get a driver in them, and hold the $599 sale price.

    LOL, thanks for the laugh. Exactly what I needed after a long day.
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  • Toolfan66
    Toolfan66 Posts: 17,234
    edited April 2022
    I should note that my comment above was only about trying to repair the passives, ‘NOT’ putting a driver in these speakers, that will not fair well at all. I missed that part of the post.

    I still stand behind there is nothing to lose at this point trying to find some material to repair them, there will be very little cost, and if it fails, they are still garbage, if it works good enough till he finds replacements, no harm no foul IMO..

    We have guys putting armacell inside driver baskets, cutting off dust caps, and apparently with positive results, trying to repair these is child’s play..
    Post edited by Toolfan66 on
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  • xschop
    xschop Posts: 5,000
    Can you weigh the old membrane?
    Don't take experimental gene therapies from known eugenicists.
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  • pitdogg2
    pitdogg2 Posts: 25,436
    Lets stop for a moment and reevaluate. When Polk did away with the foam on front for the weight they added weight in the back in the form of a bolt, possibly a carriage bolt. This bolt was in the middle of the neck of the styrofoam. I've had both SW120 and SW121, IIRC the difference was a foam front and no bolt and a plasticky front and bolt. 12" Polk passive radiators have for the most part been readily available on the auction site.
    Buy some for spares and weigh them for reference to get idea of how much material and glue you'll need to repair the set the foam was removed from.
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  • Toolfan66
    Toolfan66 Posts: 17,234
    I don't believe any foam was removed, only the thin layer of material that was bubbled that was glued to the plastic face you see in the pics above, he is just wanting to glue a replacement piece on these so they are flat not bubbled up as some do. I just think he can find a better piece of replacement material than the pieces he was wanting to use, plus that color would look horrible on them..
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  • invalid
    invalid Posts: 1,365
    [quote

    Polk couldn’t get a driver in them, and hold the $599 sale price.[/quote]


    I bet it cost Polk considerably more money to properly implement the passive radiators.
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  • Toolfan66
    Toolfan66 Posts: 17,234
    I have two sets of SW150 passives, one set has the extra weight on the back (looks like a carriage bolt) the other one doesn't.
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  • Baker
    Baker Posts: 18
    Agreed, I will look for a more “consistent to design” material.

    I do have a scale, and can match weight.

    Color... Yes, I’ll find some black.

    Cabinets are to be wrapped in Hard Maple Formica. Think very blonde...

    Thanks for the real help...
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  • pitdogg2
    pitdogg2 Posts: 25,436
    Toolfan66 Posts: 15,161
    8:30AM
    I don't believe any foam was removed, only the thin layer of material that was bubbled that was glued to the plastic face

    Yes the soft material that bubbled was the foam I was referring to. Many of that design bubbled, some very badly others just a few spots. IME it never got worse after the bubble, it just looked terrible.

    Interesting @Toolfan66 on the sw150 and the bolt no bolt. I wonder in one of them has lighter Styrofoam substrate verses to other necessitating one needing the bolt to make up the difference.

    I'm aware that the SDA SRS 2 used two different passives. Cabinet was the same only difference was drivers used. I and another member discussed it mave have been one set of drivers that made a bigger difference.
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  • BlueBirdMusic
    BlueBirdMusic Posts: 2,277
    @Baker, please don't leave this thread "hanging"; keep posting your progress.
    It is interesting.
    "Sometimes you have to look to the past to understand where you are going in the future"

    Anger is just anger. It isn’t good. It isn’t bad. It just is. What you do with it is what matters.
    You can use it to build or to destroy. You just have to make the choice.     Jim Butcher




    Harry / Marietta GA
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  • BlueBirdMusic
    BlueBirdMusic Posts: 2,277
    Quote from @Toolfan66:

    We have guys putting armacell inside driver baskets, cutting off dust caps, and apparently with positive results, trying to repair these is child’s play..


    ^^^ I like your perspective. I am still laughing from this comparison.
    "Sometimes you have to look to the past to understand where you are going in the future"

    Anger is just anger. It isn’t good. It isn’t bad. It just is. What you do with it is what matters.
    You can use it to build or to destroy. You just have to make the choice.     Jim Butcher




    Harry / Marietta GA
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