SDA 1C passive radiators

Mr. Bubbles

Hello everyone, I'm new to the forums and this is my first post. I just purchased my second set of SDA's, a pair of 1C's. At least that is what I am told and what they appear to be from pictures and such I can find. I already own a pair of 2B's(?) again I do not know how to tell for sure between some of the model designations. My 2B's sound and look great and everything appears normal.

My question is on the 1C's. When I purchased them the previous owner told me he had replaced one of the passives as the old one was torn. He ordered a pair of passives off of E-bay so he had an additional good passive, but not the old damaged one. The passives in the speakers look different so I pulled them from the cabinet. the rear of these appear the same but the fronts do not; one has the foam surface and the other appears to be hard plastic. Both are made from Styrofoam and have a metal plug in the rear. The extra good passive also has the foam surface but no metal plug. My question is which one of these passives is correct for this model. All three passives have the same rubber surround as indicated by the numbers molded in the edge. The 2 with the foam appear to be dated from '83 and the hard plastic from '87 (the best I can tell. I had to pull dynamat from the basket of this one to find the numbers written on it.)

Also the cabinet with the hard plastic radiator with the dynamat has been line with dynamat along the sides and bottom on the inside. The other appears stock. Both crossovers appear the same and do not appear to be touched but i would like to double check that since I can tell someone has previously had the speaker removed. i want to be sure it is still wired correcly. Can any of you please help me with these 2 issues. Thank you very much.

Joe08867

Hello and Welcome oliverbubbles,

The passive with the foam front is the original more than likely. The ones that have a metal plug may be aftermarket and more than likely not correct for this application. But I would need to see them to be certain.

As I do not own SDA1C's I can't help with the wiring but I am sure someone here can.

Also, if you can take pics of the crossovers and passives we can make sure the information we give is correct.

Mr. Bubbles

OK, I think I found the wiring info I need under the Stickey posted by DarqueKnight. It even contains info to be sure speaker positioning is correct per cabinet location as well as wiring to the crossover. (which is something else I was wondering about but failed to mention previously) Many thanks to him/ her(?).

Still wondering about the radiators. Do the handwritten #'s on the rear of the baskets indicate pertinent information. I'll try to get pictures this evening and put them up.

I would also like to be sure which generation units I have in both models (1C (?), 2B (?)), but from reading I have done here, I am not sure how possible that is.

F1nut

Do the handwritten #'s on the rear of the baskets indicate pertinent information.

Yes, the correct PR for your 1C's should say SW120.

Mr. Bubbles

Thank you for the reply F1nut. This leads me to know that I have only one correct radiator but still not sure if it has been tampered with. That radiator is the one with the hard plastic face and the metal plug in the rear. Does this description sound correct for this model? Again I will get some pics later in case it will help.

This leads me to wonder what the other passives I have came out of and why though they look alike for the most part, does one have the metal plug in the rear and the other one not. they both have the foam covered faces. I assume they are tuned differently for different models, but does anyone know more specifically their different characteristics?

I am not necessarily interested in having these perfectly original but do not want to negatively affect the sound in any way. If I know which passive is a correct original and not tampered with, I could then use it as a comparison to the others, without the SDA cable connected for an AB comparison.

F1nut

Polk used PR's with and without the metal plug. I believe the ones with the plug were later versions.

What is written on the back of the other two?

Mr. Bubbles

I am attaching pictures. 2 with metal plugs, both different; one has foam front panel, the other hard plastic. The Styrofoam base appears slightly different on these around the area of the metal plug. the 2 with foam fronts appear to be the same except for the metal plug so I think someone may have either put a plug in one or taken a plug out of one. The one with the plastic font also has a plug but Styrofoam around the plug extends farther back from the spider and is smaller in diameter. In the pictures it is the one with the Dynamat.

hard plastic face

all surrounds on passives have this #

#'s on unit with hard face and metal plug

#'s unit with foam face and metal plug

#'s on unit with foam face and no plug

foam face

F1nut

The one in your first picture, dated 1987, is the original PR for your 1C's.

The one in your second pic, dated 1983, is too early for the 1C's. It is from one of the following, SDA 1, SDA 2 or SDA 1A. The good news is that it is an SW120.

The one in your third pic, dated 1983, appears to be the same as #2, but it is missing the plug and should not be used.

Mr. Bubbles

The one in your first picture, dated 1987, is the original PR for your 1C's.

By this I assume you mean the first picture of the back of the radiator.

The one in your second pic, dated 1983, is too early for the 1C's. It is from one of the following, SDA 1, SDA 2 or SDA 1A. The good news is that it is an SW120.

How can you tell it is a sw120? It looks identical to the last one except for the plug. both have foam fronts. the other that appears to say SW120 and is dated '87 looks different with the plastic front and slightly different styrofoam base around where the plug is located. The 2 with the foam fronts look like the units in my 2B's from the front but I haven't pulled these from my 2B's for comparison yet. I am not sure if the 2B's use the metal plug or not.

The person I purchased the 1C's from told me he replaced the one passive but when he did he actually purchased a pair form someone on e-bay. he was told these came from a matching pair of SDA's but were unsure which model. I did not get from him whether he made any mods to either one regarding the plug as I was unaware of the plug at that time. All I had to look at was the extra radiator that he had gotten with the replacement.

F1nut

By this I assume you mean the first picture of the back of the radiator.

Correct.

How can you tell it is a sw120?

Because Polk only made two 12" PR's. The SW120 and the SW121. Yours are SW120's because of the date. The SW121's were later than 1983.

I did not get from him whether he made any mods to either one regarding the plug as I was unaware of the plug at that time.

He didn't make any mods, the plug is simply missing and that PR should not be used.

Mr. Bubbles

Thank you again. You seem to know a lot about these. I am still confused a little though; given your info, how does that explain my SW120 dated '87. Also if all of these units are SW120's why do they look different (plastic vs foam faces). From that I assume they must have made different versions of the units. If that is the case, they would seemingly be interchangeable.

F1nut

I am still confused a little though; given your info, how does that explain my SW120 dated '87.

Because the 1C's did not begin production until 1987.

Also if all of these units are SW120's why do they look different (plastic vs foam faces). From that I assume they must have made different versions of the units.

Correct.

If that is the case, they would seemingly be interchangeable.

Correct.

Mr. Bubbles

I was finally able to get back in touch with the previous owner. He received both passives with the foam fronts from the ebay seller who had removed them from a matched set of SDA's but we don't know which model. When he received them they were identical with no metal plugs in either one. He tore the old passive apart to get the plug out and put it in the one I have now with the foam front. So If all of that is correct. It would seemingly mean that the units with the foam fronts (at least the ones I have) should not have the metal plug, as one does not. And the unit with the plastic front should have the metal plug in the back. To further back this up (at least partly), on ebay, there is a pair of SW120 radiators (plainly marked) with plastic faces and the metal plugs. There is also a pair of SW121 (again plainly marked) with foam faces and no plugs. Both these pairs look virtually identical to the units I have except for the one the previous owners put the plug in.

This does not match with info from F1nut however. Being that the units I have that appear to be the same as the SW121's on ebay but mine are marked '83. Does Polk have a listing of which radiator went in which models or were they like the drivers and could be just about any combination depending on what they had at the time? I also assume their diaphragm weight would be considered proprietary info and not available.

Does anyone know what the difference between the SW121 and the SW120 is supposed to be? is it simply diaphragm weight or could it be the foam front vs the plastic front? The foam would definitely add mass to the front as well as damping, so the plug may not be necessary on those(?).

Has anyone ever tried a measured comparison between these 2 to see what the difference in tuning may be or if there is any significant difference?

Mr. Bubbles

another note to add to this; I pulled the radiators from my 2B's and they both have the foam fronts and no metal plugs and are labeled SW121 like the ones on ebay and are from '86.

F1nut

When he received them they were identical with no metal plugs in either one. He tore the old passive apart to get the plug out and put it in the one I have now with the foam front.

Ok, that changes everything. He should not have done that. Here's what I recommend, remove the plug from the '83 PR. Then, install both '83's and keep the '87 as a spare.

Being that the units I have that appear to be the same as the SW121's on ebay but mine are marked '83.

As I stated, your '83's are SW120's. The SW121 did not come out until 1985.

Mr. Bubbles

Thanks for all the info. I know when it comes down to it, it doesn't matter which passive is in there as long as the sound is right. I would just like to be sure due to the possible future collector value and/or if I decide to mod, I know where they originally started.

I had already thought I would do what you recommend F1nut. I ewill also , without the SDA cable connected try to make as good of an a/b comparison as I can with the plastic face unit installed in one of them and the foam face with no plug in the other. I aslo have an Audio control RTA from my car stereo days I can do a pink noise test on and see if there is any difference. It is limited, however, due to the bands it analyzes instead of a computer generated graph.

I will probably perform some cabinet mods at least on these since someone else has already started on one with the Dynamat.

F1nut

I'm glad we finally got it all sorted out.

I will probably perform some cabinet mods at least on these since someone else has already started on one with the Dynamat.

Do you mean someone used Dynamat on the insdie of the cabinets?

Mr. Bubbles

Yes, inside the left cabinet, On the sides approx 3/4 up from the bottom and across the bottom. None on the baffle or back. None on any drivers, just the passive with the plastic face as pictured above.

Not something I would have done to these because of possible collectors value but very similar to what we used to do in car audio to kill sympathetic vibrations in sub enclosures. It actually works well as long as a good product is used, which they did (at least in car audio it works very well, I'm sure it's the same in home audio since all basic principles are equal aside from cabin/ room gains and resonant vibrations from the listening environment.

F1nut

Hmmm....Dynamat wouldn't be my choice for the inside of a speaker cabinet.

Mr. Bubbles

mine neither, but they could have done worse.

Joe08867

How much Dynamat is in there? To much is a bad thing and it should not be placed behind the passive in any way. Trust me I have dabbled with Dyna and it is not good in the bottom of the cabinet.

Mr. Bubbles

How much Dynamat is in there? To much is a bad thing and it should not be placed behind the passive in any way. Trust me I have dabbled with Dyna and it is not good in the bottom of the cabinet.

I was originally confused on exactly where it was in the cabs, but after further inspection i found it to be on the sides of the cabinet and on the baffle in the lower portion of the cabinet. None on the bottom or back of the cabinet. I have not pulled the tweets and fiberfill to look at the top of the cab. This has been done on one cabinet only and I can hear virtually no difference between it and the cabinet with no dynamat inside.

Joe08867

It mostly helps with cabinet resonance more than anything. But if it is behind the PR it can diminish the bass response somewhat.