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  1. #1

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    Talking SDA SRS Questions

    Thankyou for allowing me to join your forum, I have a couple of questions that I hope some one here may be able to help me with. I have a pair of SDA SRS speakers that I bought new from the dealer in Melbourne Australia and I am in the middle of modifying them for a better sound.

    I have the following Quoestions:
    How do I determine the series of these speakers? Drivers are marked with March 1986 and the tweeters are the dead fish eye type.

    On stripping the cabinets I found that in a lot of cases the glued joints were only on one side and the amount of tipped in glue just run everywhere was incredible.

    On one of the speakers I have rewired the internal wiring with 12 gauge OFC good quality wire and soldered all the board and speaker connections, my question on this is that why is the polarity crossed on both the vertical Bass/Mid speakers between two and three on both sides?

    Doesn't this present a potential short of the polarity when wiring back to the crossover? I have a great deal of problems getting my head around that one if it is right. To my knowledge the cabinets have never been apart is it possible that they were wrongly wired at the factory?

    If someone could let me know what series this speaker is and what wiring configuration is correct and if possible a wiring diagram I would be eternally greatfull.

    Currently I am running these speakers in bi Amp mode with a Stax CAY pre amp and a pair of RB1090 power amps, the modifications to the first cabinet are as follows.

    All angle joint surfaces internally have been braced with 25mm Hardwood quad after all the original excess glue was removed ( literally someone just tipped a whole pot in and let it run ) then approximately 10kg of spray in body deadner coating all internal surfaces.

    Fabricated an 18mm mdf duct under the tweeters between the cutouts sealed at the top of the cabinet and open just above the crossover to allow cables to be run. put an additional 18mm mdf panel behind the ABR to give it a bit more meat.

    Replaced the speaker terminal block with a 2.5mm thick stainless steel plate fitted with three sets of gold lock h/d binding posts for both bi amping and SDR Cable.

    Cut and rolled two sets of five thick 25mm Dacron filling fitted under the Bass/Mid drivers full length of the cabinet, silicone sealed the top timber section of the cabinet so no vibration.

    As I have only modified one cabinet so far I wanted to gauge the difference between the two a little hard to gauge just yet as the amps are brand new and sounded very harsh at first but as the night wore on it all started to mellow.

    The modified speaker has less volume at the same setting but showed a distinctly tighter more defined sound and the tweeters sounded more defined and less shrill at volume.

    As for image it appeared to be slightly to the right but I am not convinced that all is right in that area as it still doesn't sound quite right so I need some help.

    Thankyou in advance and I look forward to being a part of this forum.

  2. #2

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    Try posting in the vintage speaker area. There are many poeple who can answer all your questions. I am not one of them. Welcome to the forum. Jeff

  3. #3

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    Quote Originally Posted by Loco57 View Post
    I have the following Quoestions:
    How do I determine the series of these speakers? Drivers are marked with March 1986 and the tweeters are the dead fish eye type.
    Post a picture, that would help. Also visit polksda.com maybe that site can help you id them.

    Quote Originally Posted by Loco57 View Post
    my question on this is that why is the polarity crossed on both the vertical Bass/Mid speakers between two and three on both sides?
    Not sure what you are saying, but the polarity should not be reversed was this on one speaker or both?

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  4. #4

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    Thankyou Gentlemen good information, I will try to post a picture to give a better idea of what series these speakers are. With regards to the wiring question the original wiring is daisy chained ( so to speak ) and crosses the polarity from positive to negative on the second and third speaker connection on both right and left speaker bank.

    So not sure what gives on this just doesn't seem right to me, measuring the impedence across the speakers is all over the shop!

  5. #5

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    SDA speakers are wired like that; positive from some drivers to negative from others. Don't have the specifics now, but that's how they were in every SDA speaker I've owned.

    Here's just an example from my 3.1's:

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  6. #6

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    Wire them according to the schematic. The dimensional drivers run out of phase and that is probably why the polarity on some of the drivers is different than a conventional speaker. Study the schematic closely and if you are doing only one speaker at a time use the unmolested x-over as a reference.

    Also if you are using high quality replacement caps you can get rid of the silver mica bypass caps that are originally wired in on the factory x-over.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

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