Just acquired some SDA SRS 2's one tweet is toast...

Chrisssssssss Posts: 11
edited November 2021 in Vintage Speakers
Hey all,

I just recently got a pair of SDA SRS 2's (2nd gen pin/blade units) locally here in BC Canada and really looking forward to playing with these beasts and modding them for the better. They are in decent overall shape... but one tweet is out. I heard and read all about the new replacement tweets (silk dome) and was wondering about going a slightly different route and wanted some opinions.

I have had all sorts of speakers from all different manufacturers in both Car and Home audio. To me personally I have always used old school MB Quart car audio speakers and absolutely love the sound of their 1" titanium dome tweeters. Long story short, I would like to use some MB Quart 1" titanium tweeters in these bad boys and take out the stock SL2000 units. I have narrowed it down to these guys just due to availability and price... BUT I have some concerns about using them. Since they are 6 ohm drivers, I assume there would be issues with the crossover due to this difference. My questions are:

1) If I were to replace both the stock 8 ohm tweets with these 6 ohm ones as is, what will be the difference in specs and response of the speakers and stuff? What does it do to the crossover point? Does it lower or raise the point that the tweeters are xover'd at? Would it make the tweeter louder or more volume overall in the speaker as a whole? What would it do to the overall ohm load of the speaker as a system? I assume it would lower the resistance. Basically asking what would be the result if I left everything as is on the xover how would it affect the speaker sound overall?


2) What if I just replaced one in each speaker and left one stock? I assume the 6 ohm driver would probably be louder compared to the 8 ohm one... but isn't one of the tweeters in the speaker already slightly lower in volume than the other one?

3) I have a pile of car audio tweeters that are spares and have several 4 ohm tweeters that I was contemplating using in this system just for giggles and if I were to wire 2x 4 ohm tweeters in series I would get an 8 ohm load - so if I were to wire in 8x 4 ohm tweeters (2x 4 ohm tweeters to replace each of the stock 8 ohm tweeters in the speaker resulting in 4x 4 ohm tweeters in each speaker - if I somehow make a panel or some sort of adapter plate to mount them where the stock ones were - what do you think the result would be here? It would match the stock 8 ohm load per tweeter connection so there wouldn't alter the crossover specs so it should work out technically similar.

4) I also have one other love interest... a Heil AMT (Air Motion Transformer) tweeter. I have a pair of AMT's that I have been dying to use in a speaker. I am planning on making a speaker design of my own that will be using these as the tweeter but I think I would love to use these in this speaker. Since I only have a single pair of these, and they are 8 ohms. I was contemplating on just wiring them to a single connection and take out the stock units and let these sing in their place while still leaving one of the stock pair of tweeters connected. Or even buy a second set of AMT's and replace both stockers with AMT's and see what this sounds like.

I know I know what you guys are all gonna say: I should leave them alone and just replace them with the new ones that are supposed to go in their place. I will likely end up doing that in the long run, but I am also the type of person that loves to tinker and experiment with the sound and make it better by upgrading and tailoring it to my own personal sound preference. I personally like the sound of a titanium over a silk dome and an AMT overall. I will likely end up Bi-Amping them so I will be able to adjust the levels of the tweeters and lows to match.

Anyways I just thought I would post my ramblings on here and see what kind of thoughts (if any lol) I get and go from there. I am looking forward to hearing from anyone that feels like chiming in - even if it is just to say hi.

Chris Nicholls

Polk SDA 1C's
Sony GX99ES Receiver
Sony CDP X555ES CD Player
Large MB Quart Speaker collection!


  • "I know I know what you guys are all gonna say: I should leave them alone and just replace them with the new ones that are supposed to go in their place."

    That's what I would do.
    SDA SRS 1.2TL's
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  • F1nut
    F1nut Posts: 46,511
    I know I know what you guys are all gonna say: I should leave them alone and just replace them with the new ones that are supposed to go in their place.
    That is the one and only correct decision.
    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

  • Gardenstater
    Gardenstater Posts: 2,172
    edited November 2021
    Either you need the skills and experience of a speaker designer/engineer or you need to have some sort of blind luck :) Pretty sure there is a lot more to it than nominal impedance. You need to know the impedance curve vs frequency and the spl vs frequency with a given wattage input for both the SL2000 and the tweeter in question. Then you need to test the in room frequency response result with various XO modifications to get the desired result. If you want to know more about this stuff, I'd go over to DIYaudio.com because I have never done this. Maybe someone here has but you are going to be much better off going with the Polk engineered replacements unless you like the thrill of the chase and the agony of the defeat.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
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  • VR3
    VR3 Posts: 25,100
    Just imagining a1.2tl with buttery toast for tweeters @Hermitism
    - Not Tom

    "No, that's silly talk. Dude, you can't possibly be this audio dumb so quit the act." - Doro
  • TroyD
    TroyD Posts: 12,763
    edited November 2021
    Please. For the love of God. Don’t.

    Frankenstein-ing is almost always a terrible idea.

    I plan for the future. - F1Nut
  • xschop
    xschop Posts: 2,184
    edited November 2021
    Wuhan silks aren't bad. Titanium is for race cars and bad hips.
  • engie490
    engie490 Posts: 149
    As noted above, there's a lot more to integrating a different tweeter than matching the "8 ohm" impedance of the Polk tweeter:

    Does the tweeter physically fit the current cutout in the speaker baffle? Remember, it needs to create an airtight seal for the bass drivers. If it's bigger than the current tweeter, you're going to have a heck of a time making that seal happen.

    What's the sensitivity? Does it needed to be padded down to match the midrange?

    What's the dispersion pattern (both vertical and horizontal)?

    What's the resonant frequency for the tweeter you want to use?

    What's the power handling?

    What's the slope of the Polk's high pass crossover for the tweeter circuit? This impacts how much energy the tweeter sees as it is rolled out below the crossover point.

    Are there any discontinuities in the frequency response that will require correction?

    The AMT is a sizable dipole and is best used atop a speaker cabinet, but the Polk SDA cabs would be a poor choice for this as the tweeters would be over 50" off the floor. The use of a dipole would also be problematic given the Polk is designed to be placed very close to the rear wall.

    All that said, you can try anything you want. The most likely casualty would be the new tweeter from overdriving it.
    Polk SDA SRS 1.2TLs
    Rowland Model 8
    Rowland Synergy IIi
    Oppo BDP-105 (using as a DAC)
    Innersound Phono (actually Coda FET-03p)
    Technics Sp-15 with Jelco 10.5 arm
  • I believe it has been a loooong time since MB Quart made good stuff. I recall they sold out some time last century (no kidding). I am not a car audio expert, but I did listen to their stuff when I last had a decent car stereo, circa 2002. Based on their early-mid 90 reputation I made the mistake of putting quart coaxial 6.5s in my rear doors. They didn't sound great and they died pretty quickly. I didn't bother with any sort of warrantee claim, just moved on to something better.
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