SDA SRS Tweeter Response Curves

As mentioned in a previous thread I am in the process of restoring a pair of SDA SRS speakers. The schematic I am working from that matches the crossover is from 8/14/85, that in combination with the Blade/Blade interconnect brings me to the conclusion that these are first generation.

That being said I have built up an audio spectrum analyzer system based on True RTA 1/3 octave software and have found it to be a useful troubleshooting tool.
I have measured the response curves of all of the drivers and found two defective tweeters.
One was obvious it was open circuit had no sonic output.

I purchased a replacement from a seller on line who had what he claimed was a "NOS" (new old stock). I believe this is true because under the microscope the terminals showed no witness marks (scrapes) that being connected would cause. It was also in original carton and the unit is pristine clean.

However when you look at the curves in that attached PDF this tweeter (High Freq. Line Source #3) seems to have an extended low end response. It seems to be a bit more energetic in the 10 kHz range and does not drop off as quickly as the two assumed good tweeters do.

So my question is: Do I have a legitimate complaint or is this inside the range of driver to driver variability?

My second question is related (High Freq. Line Source #4).
This driver is visibly damage as illustrated the dome is separating from the perimeter. Is anyone aware of a repair for this. I am thinking a small bead low viscosity silicone???
Any suggestions are welcomed.

Thanks for your time and interest.

Comments

  • F1nutF1nut Posts: 41,943
    The SL2000 tweeter is nasty. Replace all of them with the RD0194.
    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."


  • MrwolfMrwolf Posts: 11
    Will this require crossover changes?
  • pitdogg2pitdogg2 Posts: 13,489
    Mrwolf wrote: »
    Will this require crossover changes?

    no direct replacement and 10x better than SL2000 tweeters.

  • F1nutF1nut Posts: 41,943
    pitdogg2 wrote: »
    Mrwolf wrote: »
    Will this require crossover changes?

    no direct replacement and 100x better than SL2000 tweeters.

    Fixed :)
    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."


  • Tony MTony M Posts: 8,123
    edited June 11
    I've fixed the separation issue on a couple of fish-eye SL's with Eileen's tacky glue. Works GREAT.
    3fl2kmf9monn.png

    But the RD0194's sound softer and have detail too. No harsh brightness.
    It takes a couple of weeks for their sound to get louder I believe. ;)

    They're worth the money if you have it.
    Most people just listen to music and watch movies. I EXPERIENCE them.
  • tonyp063tonyp063 Posts: 633
    edited June 11
    @Mrwolf , I'm going to point you to this.

    https://forum.polkaudio.com/discussion/182943/the-tale-of-5-tweeters-sda-tweeter-replacement-guide/p1

    The person who wrote it is known & respected for his knowledge & methodology.
  • Tony MTony M Posts: 8,123
    Aleene's ... :s
    Why can't I ever remember how to spell this name?!
    Even when it's on the bottle in a picture I post in the same post? :s
    Most people just listen to music and watch movies. I EXPERIENCE them.
  • codycatalistcodycatalist Posts: 2,410
    Tony M wrote: »
    Aleene's ... :s
    Why can't I ever remember how to spell this name?!
    Even when it's on the bottle in a picture I post in the same post? :s

    I’m sure you were listening to Dexys Midnight Runners when making the post. You are forgiven.
    Just a dude doing dude-ly things

    "Temptation is the manifestation of desire which equals necessity." - Mikey081057
    " I have always had a champange taste with a beer budget" - Rick88
    "Just because the thread is getting views don't mean much .. I like a good train wreck doesn't mean i want to be in one..." - pitdogg2
    "Those that don't know, don't know that they don't know." - heiney9
    "Audiophiles are the male equivalent of cat ladies." - Audiokarma Member
  • MrwolfMrwolf Posts: 11
    Thank you to all that responded.
    I appreciate the recommendation to replace the SL2000 with the current production.
    However as I am not likely to do that for only one or two tweeters, I still need to troubleshoot the root cause of the response curve differences.
    That being said I would like to go back to the top of the post.
    I have one anomalous tweeter circuit out of eight.

    Please see attached document. This is a copy of an e-mail I sent to Polk customer service.

    As an aside comment, After I sent the e-mail to Polk Customer Service, I received an automated receipt conformation with the statement that I would be contacted "Soon".
    I am not sure what the word soon means on planet Polk, but if any one from Polk is monitoring this forum, please note, it has been ~ 2 wks with no further communication. I am an adult and no is an acceptable answer to a question, making a promise and not keeping it is not.

    So moving on,
    If the kind folks of the forum would please take a look at the attached document,
    Any suggestions would be greatly appreciated.

    Best Regards,
    Mrwolf
  • pitdogg2pitdogg2 Posts: 13,489
    the tweeters are hotter towards the top and quieter towards the bottom as designed. Is that what you are referring to? If all tweeters were as hot as the top it would be a VERY bright speaker and not pleasant to listen to.
  • F1nutF1nut Posts: 41,943
    I still need to troubleshoot the root cause of the response curve differences.

    The tweeter array is a progressive point source. You should have different response curves.
    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."


  • MrwolfMrwolf Posts: 11
    Thank you for the discussion.
    I am not talking about sound pressure (volume). I am talking about the frequency response curve. I understand the comment from Pitdogg2 and that is more or less explained by the difference in series impedance resulting from the differences in the resistance, inductance ,and capacitance from circuit to circuit.
    I would not be surprised that F1nut is correct, however I have only one tweeter out of 8 that has a different frequency response curve.
    The other seven are nearly Identical. (Within a few db across the spectrum.)

    The tweeter in question is producing sound in a range that is expected to be below the crossover point. (100hz to 1Khz)
    That's my concern.

    Please note that the "As found" condition of the speaker was that this tweeter had an open voice coil. I suspect that may be because it was being driven with low frequency energy, therefore after I replaced the tweeter. I then recorded the curve and it was visibly different, suspecting a bad used tweeter I swapped the tweeter with a known good one (matched the others). The problem stayed in the location and did not move with the replacement tweeter.
    After swapping the tweeter with one that created a normal response curve with no change, I replaced the crossover components to no avail.

    So here I am, confused. In the words of the great philosopher Spock after you eliminate the possible you must consider the impossible.
    I possibly hosed up the experiment??

    So unless there is a fresh thought, I will redo the swap experiment to confirm outcome.

    Best Regards
  • F1nutF1nut Posts: 41,943
    Pitdogg2 and I are talking about the same thing, progressive point source. The frequency responses should be different for each tweeter in the array.

    That said, since you have swapped tweeters and changed some of the caps (not sure why you used inferior electrolytics again) may I suggest swapping the crossovers to see if the issue follows. If it does follow the problem is in the crossover.
    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."


  • delkaldelkal Posts: 537
    edited July 12
    You can't try and match the tweeters while they are still in the speaker. If you think there is a problem you will have to take them all out and match them without any crossover components inline.

    After a quick look at the schematic 3 tweeters should play at different volumes (different resistors) and 3 have different inductors / capacitors with the various resistors that will change the frequency response. I also don't understand why your T1 and T2 match up so well. My guess is that T2 and T3 should sound closest but at a much lower volume than the other tweeters. Are you sure you have your numbering correct according to the schematic?

    On the plus side. If you do match your tweeters you can try and install them in matched pairs with the same response on each speaker. This could be worth the effort. And if any tweeter is off install them in a position with the 22 ohm resistor (it won't be playing as loud)

  • SchurkeySchurkey Posts: 1,875
    Mrwolf wrote: »
    The tweeter in question is producing sound in a range that is expected to be below the crossover point. (100hz to 1Khz)
    That's my concern.
    Wouldn't that require a shorted capacitor in the crossover?
  • MrwolfMrwolf Posts: 11
    Schurkey, I agree, and that is why I replaced C4 and C5 and R6 for good measure (On both the left and right crossovers).Please see schematic attached above.

    F1nut, I take your point however I am restoring, not upgrading. Therefore my current goal is to return the speakers to their original state. I used as close to original parts as practical. Polyester film 10% and silver mica 5%.

    Delkal, Thank you for your observation.
    That is precisely why this is so odd, I agree that your statement makes sense. I will confirm the numbering and rerun the “response curves”,
    I will set the software to use something that is absolute in terms of sound pressure.

    But, I don’t have 2 that appear to be alike in terms of frequency response, I have 7.
    Please note that there are 3 in the left speaker, and 4 in the right speaker with the same curve. (Relative sound pressure unknown)
    So if I apply Occam’s Razor, I have one anomalous tweeter circuit. (Or seven???)
    I will rerun the curves to make sure I am not **** it up.

    With all of this being said I have a discussion with Polk engineers scheduled for next week. I will let you know what they say.

    Thanks for the collaboration I am now better prepared for the discussion.
    Best Regards
  • F1nutF1nut Posts: 41,943
    F1nut, I take your point however I am restoring, not upgrading. Therefore my current goal is to return the speakers to their original state.

    Restoring is a waste of time and money when the improvements from upgrades are well documented and very audible.
    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."


  • pitdogg2pitdogg2 Posts: 13,489
    Why waste time putting the inferior cost conscious parts Polk used to hit a price point? Honestly it just makes no sense to me. My 2.3tl's are night and day different from stock with just better polypropylene caps (Sonicaps)and Vishay-Mills resistors.
Sign In or Register to comment.

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!