Passive Radiators SW150, 155 - SW 120, 121, 122

inspiredsports

I've noticed there are different modes of both 12' and 15" passive radiators in play on various Polk models. I'm guessing their are design specs somewhere relating to stiffness of the suspension or something like that.

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The SDA-1A and SDA-2B use the SW121 for instance, where the slightly larger volume cabinet SDA-2, SDA-1, SDA-1A, SDA-1B and SDA-1C use the SW120.

- - - I own SDA-2B' with the SW121, but have a shot a buying some spare SW120's. I wonder how the bass sound would be changed if I substituted? (I would only do this if I needed a spare due to damage)

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The same seems to be true for the SW150 used mostly in the bigger SDA SRS 1 series, and SW155 used mostly in the smaller SDA SRS 2 series (with the exception of the first 1986 SDA SRS 2 that used the SW150.

The 1986 SDA SRS 2 (that I own) is what puzzles me. Polk must have learned that the SW150 works better in a larger cabinet in 1987.

- - - I wonder what the sonic difference would be if I could ever find some SW155's for my cabinets? This is a swap I would be more likely to do as it seems the SW155 is better suited to the "2" series.

I know the SW150's would be easily resell as every 1.2 owner seems to want a spare, but I know SW155's would be rare as it doesn't make sense to sacrifice a cabinet unless there has been some kind of rare irreparable damage that didn't hurt the drivers.

inspiredsports

I have SDA-2B's modded to use the RDO198-1 that originally use the 12" SW121 Passive Radiator. Everything else the same, the 198's kick out probably 2-3 more db's of smooth, sweet treble than the original SL2000's did.

I picked up a pair of 12" SW120's that the seller had parted out from a water damaged SDA 1B on eBay a few weeks ago that are designed to work with the SDA 1, 1A, 1B and 1C. It may be that the 120's are simply designed for the larger area 1 Series cabinet volume, but my thought process was that they might also kick out a bit more bass in my 2B's.

I've noted 2 main differences between the original SW121's and the eBay SW120's:
1) When I gently depress the 120's, the flex property seems to be STIFFER (more force required to push them in).
2) The 120's seem to have an additional 9-1/8" diameter "high density foam" layer glued on top of what is the final broadcast surface of my 121's. This extra layer appears to be factory installed, but I have no way of knowing for sure.

OK, so tonight I removed my left channel (Mortited and Dynamat Extremed SW121) and Mortited one of the eBay 120's in its place (no Dynamat Extreme as I am out and have more on order).

I tried some stereo tests, mono tests and all left/right tests. Bass is so non-directional I was not 100% certain there was a noticeable change, but the "all left test" sounded quite good.

I went ahead and changed out the right channel and listened to music for about an hour and tested tones down to 20Hz with my Stereophile Test CD. Then I switched back to the original 121's for about an hour. I then switched to the 120's and have been listening for over 2 hours now.

My "TL'd" SDA-2B's sound BETTER with the SW120 Passive Radiator. Slightly more bass overall, and the tonal quality of the bass is tighter, more responsive. The bass seems to match up better with the 198's output.

I need to verify if the extra dense foam layer is "factory", and if that is the only difference between the SW 121 and SW 120.

Systems

inspiredsports wrote: »

I've noticed there are different models of both 12' and 15" passive radiators in play on various Polk models. I'm guessing their are design specs somewhere relating to stiffness of the suspension or something like that.

A PR's tuning is determined by the cabinets internal volume and the weight or moving mass of it's diaphram.So its probable that each PR has a diaphram of a specific weight so as to work best in certain models cabinet volumes.

inspiredsports

That's what I would have thought too, but the anomaly cited in my post #1 wherein the SW150 (normally reserved for the FAR LARGER SRS series) is quite successfully used in the 1986 SDA SRS 2 breaks that theory down just a bit.

Does anyone have a take on that thin layer of high density foam I mentioned in item 2) of paragraph 3 in my Post #2 ??

F1nut

I believe another factor in determining which PR works best would be the choice of mid-drivers.

Does anyone have a take on that thin layer of high density foam I mentioned in item 2) of paragraph 3 in my Post #2 ??

If it's black, it's factory.

Systems

F1nut wrote: »

I believe another factor in determining which PR works best would be the choice of mid-drivers.

Yes it is.

inspiredsports

Thanks. It is black, and that confirms what I thought as it is a perfect circle and so professionally installed. I didn't think it could have been an aftermarket tweak.

I picked up the SW120's, plus some 6.5's and crossover parts that fit my old SRS 2's from a local guy who had them on eBay thinking the 120's would help someone in the group, but I like the sound so much I may give them a permanent home in my 2B's.

I'm out of Dynamat Extreme and have some on order, so in about a week when it arrives I can conduct some "apples for apples" testing, but I seem to prefer the sound of the 120's versus the stock 121's better at this point in time.