SDA-SRS, SRS 1.2, SRS 1.2TL, SRS 2.3TL Crossover Design and Progressive Point Source

decato
decato Posts: 180
edited January 2007 in Vintage Speakers
Introduction

There has been a lot of discussion about which SDA-SRS crossover is best. There has also been some mystery around Progressive Point Source technology. As I continue to learn more about speaker design, I thought I would share some of the latest knowledge I have acquired. According to Polk’s brochure for the SRS series featuring the trilaminate tweeter,
"… the SRS 1.2TL and 2.3TL utilize Polk's Progressive Point Source technology to maintain Constant Vertical Directivity of mid and high frequencies, which prevents undesirable beaming. As frequencies increase, the tweeter array adjusts its radiation area and eventually becomes an ideal point source at the very highest frequencies, eliminating frequency interactions and reflections between multiple drivers."

For the SRS, SRS 1.2, and SRS 1.2TL, I have provided graphs illustrating the frequency response of each tweeter as well as the composite response. A DC resistance of 7.5 ohms was used for the RD0194-1 (SL2000) tweeters while 5.6 ohms was used for the RD0198-1 (SL3000) tweeters. It is interesting to note how the composite response varies among the three models.
Figure 1: SDA-SRS Schematic
Figure 2: SDA-SRS Frequency Response
Figure 3: SDA-SRS 1.2 Schematic
Figure 4: SDA-SRS 1.2 Frequency Response
Figure 5: SDA-SRS 1.2TL Schematic
Figure 6: SDA-SRS 1.2TL Frequency Response


Project

I have always preferred the sound of the 1.2TL over the 2.3TL, mainly because I thought the 2.3TL sounded slightly harsh in the treble. I can now visualize what I was hearing, as there is a small spike in the response of each of the tweeters around 2 kHz. See Figures 7 and 8.
Figure 7: SDA-SRS 2.3TL Schematic
Figure 8: SDA-SRS 2.3TL Frequency Response

A while back I posted a thread about modifying the 2.3TL into a system more like the 1.2TL. I now wish to revisit that project. It is possible to make the 2.3TL sound almost identical to the 1.2TL. The formula, first discussed in http://www.polkaudio.com/forums/showthread.php?t=35433, is now as follows:
  • Make the low-pass section of the crossover identical to the 1.2TL crossover.
  • Use 4 MW6503s for the stereo array.
  • Use 2 MW6510s for the dimensional array.
  • Follow the schematic in Figure 9 for the high-pass section of the crossover. It will yield the composite frequency response seen in Figure 10, which is almost identical to that of the 1.2TL. Each tweeter’s output increases successively just like in the 1.2TL. The only difference if that there are three instead of four tweeters. Moreover, the phase of the 1.2TL has been maintained in this design.
  • Applying Soundcoat and adding additional bracing is still a welcome change.
Figure 9: Modified SDA-SRS 2.3TL Schematic
Figure 10: Modified SDA-SRS 2.3TL Frequency Response

How does it sound? Very much like the 1.2TL. How does the 1.2TL sound? Well, you know the answer to that question!

Here are some pictures of the modified crossover. A few components are on the underside of the board. The only drawback to this project is that it is somewhat difficult, as the layout for the high-pass components changes drastically. If you are up for a rewarding challenge, please give it a try. I guarantee you will like what you hear!
Figure 11: SDA-SRS 2.3TL Crossover - Top
Figure 12: SDA-SRS 2.3TL Crossover - Front
Figure 13: SDA-SRS 2.3TL Crossover - Side
Figure 14: SDA-SRS 2.3TL Crossover - Back

- Brian Borowski
Post edited by decato on
«1

Comments

  • schwarcw
    schwarcw Posts: 7,328
    edited January 2007
    Nice writeup Brian! I'm always impressed by your research and pursuit of improving the big SDA's. I enjoy it!:)

    After I upgraded my 2.3 crossover with Sonicaps, which are physically larger caps than the originals or Solens, I decided that if I even did this again that I would start with building a new board to avoid the mess of caps hanging for dear life over the edge, up in air, etc. Did you give any consideration to using a new board with point to point wiring?

    I'm not trying to derail the thread, I'm curious as I know you have worked a lot on various combinations and modifications.

    Thanks!
    Carl

  • DarqueKnight
    DarqueKnight Posts: 6,760
    edited January 2007
    Excellent writeup Brian. What effects on bass response do you expect from installing a 1.2TL crossover in a smaller cabinet?
    Proud and loyal citizen of the Digital Domain and Solid State Country!
  • decato
    decato Posts: 180
    edited January 2007
    schwarcw wrote:
    Did you give any consideration to using a new board with point to point wiring?

    Hi Carl,
    No, actually. This board seems to be working well. One thing that made it easier for me was that the older Solen capacitors had lengthy flexible leads. I made some modifications recently, after Solen had switched to standard tinned copper leads, but the bulk of that huge stack was already in place.

    The board is a bit heavy with the 16 awg inductors on it. I wish Polk had used regular screws like they did in the 1.2TL instead of plastic clips. However, so far everything is holding up just fine.

    -Brian
  • decato
    decato Posts: 180
    edited January 2007
    Excellent writeup Brian. What effects on bass response do you expect from installing a 1.2TL crossover in a smaller cabinet?

    Thanks, Raife.

    To answer your question, there was no discernible change in the bass response of the 2.3TL. The low-pass section of the 2.3TL crossover is quite similar to that of the 1.2TL. The only change came when I switched the inductors over to 16 awg (from the default 20/18 awg). I did not bother upgrading the 16 mH inductor as I did in the 1.2TL because I observed that at very low frequencies, the excursions of the two dimensional drivers exceeded that of the four stereo drivers. An inductor with even less DCR might cause the dimensional drivers to bottom out early.
  • F1nut
    F1nut Posts: 49,708
    edited January 2007
    You've got my wheels spinning.
    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

  • Toka78
    Toka78 Posts: 192
    edited January 2007
    Great work, Brian! Who said the SDA was dead? :)
  • RichCanDo
    RichCanDo Posts: 177
    edited January 2007
    Recently obtained the SDA 2nd Ed. Compendium. Great work! Noticed the schematic for the 1.2TL is not as shown above. Was going to PM DarqueKnight about this, but this appears a good place to post. Factory schematic in Compendium shows for the tweeters, the Positive speaker binding post ending at the Negative speaker terminal. - Negative binding post to Positive tweeter terminals. The reverse of what is shown above.

    Above appears correct to me. If so, the factory schematic is wrong. Someone once told me that the binding posts on some speakers leaving the factory had the polarity reversed. If true, it would have been because they were wired at the factory per an incorrect schematic.

    Hoping DarqueKnight reads this and can let those with Compendiums know whether the 1.2TL schematic in Compendium is correct or incorrect. Polarity for the 2.3TL is also reversed between binding posts and tweeters in the Compendium schematic.

    Edit: spelling!
    Mains; SDA 1.2TL Silk Domes, upgraded xover, biamped w/DBX BX1 200wpc
    Pre-amp: DBX CX1
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  • DarqueKnight
    DarqueKnight Posts: 6,760
    edited January 2007
    In the far recesses of my mind I seem to recall discussing with Ken Swauger the out-of-phase tweeter situation. I think it had to do with some phase shift between the LF and HF sections of the X-over and wiring the tweeters backwards set everything right again.

    I will ask Ken to verify. I would expect that a typo of that nature would not get past multiple levels of approval.
    Proud and loyal citizen of the Digital Domain and Solid State Country!
  • Polk65
    Polk65 Posts: 1,405
    edited January 2007
    Excellent post Brian.

    Here's some nude cousin's. ;)

    Steve
  • george daniel
    george daniel Posts: 12,096
    edited January 2007
    Great post,,got me thinking about my brothers 2.3 tl's :cool:

    Another cousin from the deep south
    JC approves....he told me so. (F-1 nut)
  • decato
    decato Posts: 180
    edited January 2007
    I have updated the diagrams for the TL series. The tweeter polarity is now reversed, just as it is in the schematics.
  • Larry Chanin
    Larry Chanin Posts: 601
    edited January 2007
    decato wrote:
    For the SRS, SRS 1.2, and SRS 1.2TL, I have provided graphs illustrating the frequency response of each tweeter as well as the composite response. A DC resistance of 7.5 ohms was used for the RD0194-1 (SL2000) tweeters while 5.6 ohms was used for the RD0198-1 (SL3000) tweeters. It is interesting to note how the composite response varies among the three models.

    - Brian Borowski

    Hi Brian,

    Very impressive research.

    Would you mind describing how you measured the frequency responses?

    Thanks.

    Larry
  • decato
    decato Posts: 180
    edited January 2007
    Would you mind describing how you measured the frequency responses?
    Hi Larry,
    The frequency response was not measured. The curves represent the simulated responses of the tweeters as dictated by the given crossover circuitry.
  • Hi,
    I am brand new to the poke discussion board, forgive me if I’m doing this wrong but I hope this is the thread where I might be able to get my question answered. I have a pair of poke SDA-SRA 2.3TL That I’ve had probably 7 years, my question is this I understand that there might be someone on this site who sells replacement boards for caps and transistors. I’m not sure if they need to be replaced or not Sense I have no point of reference but I also want to make sure that they are working at their best.
    If there is such a person I would really appreciate their contact information and if I’m on the wrong thread please direct me to the right one thank you very much for your time. Neil
  • txcoastal1
    txcoastal1 Posts: 13,124
    Those were Gimpods boards, which are no longer produced

    We do have someone who rebuilds crossovers

    @VR3
    2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
    Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
    Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
    Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC

    erat interfectorem cesar et **** dictatorem dicere a
  • F1nut
    F1nut Posts: 49,708
    edited December 2021
    Neil, welcome to the Polk forum. Your speakers are SDA SRS 2.3TL.

    The aftermarket boards are no longer available. However, members westmassguy and VR3 do crossover upgrades, so try reaching out to them.
    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

  • txcoastal1
    txcoastal1 Posts: 13,124
    @F1nut ...Jesse your a slacker

    :p:p:p
    2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
    Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
    Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
    Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC

    erat interfectorem cesar et **** dictatorem dicere a
  • BlueFox
    BlueFox Posts: 15,251
    ...
    Lumin X1 file player, Westminster Labs interconnect cable
    Sony XA-5400ES SACD; Pass XP-22 pre; X600.5 amps
    Magico S5 MKII Mcast Rose speakers; SPOD spikes

    Shunyata Triton v3/Typhon QR on source, Denali 2000 (2) on amps
    Shunyata Sigma XLR analog ICs, Sigma speaker cables
    Shunyata Sigma HC (2), Sigma Analog, Sigma Digital, Z Anaconda (3) power cables

    Mapleshade Samson V.3 four shelf solid maple rack, Micropoint brass footers
    Three 20 amp circuits.
  • JayCee
    JayCee Posts: 1,474
    edited December 2021
    Very interesting thread. I joined the forum in 2009 and, in all my years since, don't remember reading this. @decato, et al, Is this still considered a relevant/successful mod????
    edit to add...most impressive, you prompted this:
    F1nut wrote: »
    You've got my wheels spinning.

    Speakers: Polk1.2tl's (Uber Mods) Pre/Amp/DAC: PS Audio BHK Signature & 250, DirectStream Cables/IC's: MIT S1Bi-Wire/S1 Balanced +Avel Lindberg 1000VA "Dreadnought" Power Conditioner: PS Audio P15 Power Plant Power Cords: Core Power Technologies Gold, DH Labs Power Plus DIY w/Neotech NC-P301 & P311ends Streaming: Roon ROCK on wifi'd NUC, TP-Link WAP, & Uptone EtherREGEN, AfterDark, Emperor Double Crown Clock, Black Modernize LPS, PS Audio AirLens⟿Ω☯☥☮⟿🔊♩♪♫♬♩♪♫♬♩♪♫♬
  • Toolfan66
    Toolfan66 Posts: 16,834
    I joined in 09 as well, and I have never seen this thread..
  • decato
    decato Posts: 180
    JayCee wrote: »
    @decato, et al, Is this still considered a relevant/successful mod????

    I still have the pair with this mod in place all these years later. I think they sound fine. It was a fun exercise tweaking the crossover network to get three tweeters in the 2.3TL to cover the same range as the four in the 1.2TL. I don't recall ever hearing of any forum member reproducing this effort.

    Over the years I also modified the SRS 3.1TL, Monitor 5 Series 2, and Monitor 5jr+ Series 2 speakers, but I never got around to posting the schematics.
  • xschop
    xschop Posts: 4,636
    Just read this for the first time also. Ingenuitive modification. Should be in the SDA mods thread.

    I for one, would like to see what you did to the 5Bs. Thanks for sharing your work.
    Don't take experimental gene therapies from known eugenicists.
  • JayCee
    JayCee Posts: 1,474
    decato wrote: »
    JayCee wrote: »
    @decato, et al, Is this still considered a relevant/successful mod????

    I still have the pair with this mod in place all these years later. I think they sound fine. It was a fun exercise tweaking the crossover network to get three tweeters in the 2.3TL to cover the same range as the four in the 1.2TL. I don't recall ever hearing of any forum member reproducing this effort.

    Over the years I also modified the SRS 3.1TL, Monitor 5 Series 2, and Monitor 5jr+ Series 2 speakers, but I never got around to posting the schematics.
    "Fine" as in very good or meh, they don't suck?
    xschop wrote: »
    I for one, would like to see what you did to the 5Bs. Thanks for sharing your work.
    Ditto, and would be interested in your other projects.
    Speakers: Polk1.2tl's (Uber Mods) Pre/Amp/DAC: PS Audio BHK Signature & 250, DirectStream Cables/IC's: MIT S1Bi-Wire/S1 Balanced +Avel Lindberg 1000VA "Dreadnought" Power Conditioner: PS Audio P15 Power Plant Power Cords: Core Power Technologies Gold, DH Labs Power Plus DIY w/Neotech NC-P301 & P311ends Streaming: Roon ROCK on wifi'd NUC, TP-Link WAP, & Uptone EtherREGEN, AfterDark, Emperor Double Crown Clock, Black Modernize LPS, PS Audio AirLens⟿Ω☯☥☮⟿🔊♩♪♫♬♩♪♫♬♩♪♫♬
  • decato
    decato Posts: 180
    JayCee wrote: »
    "Fine" as in very good or meh, they don't suck?

    Fine, as in very good, smooth, non-fatiguing.

  • pkquat
    pkquat Posts: 742
    Thanks to @neil3305 for finding this and digging it up and @decato for the work. To make it easier here is a working link to @decato 's Polk SDA-SRS 1.2/2.3TL Modifications post, https://forum.polkaudio.com/discussion/35433 (until the forum changes again) . I too am interested in what the M5 S2 and M5jr+ S2 mods are. They have the same drivers and I have wondered how they would sound if the crossovers were switched.

    @decato Have you, or can you look at how the SDA SRS 2 (&1C) crossover would be modified for a TL upgrade, i.e. using the 198 tweeter vs. the 194. I figured the information is there in the crossovers, comparing the 1.2 to the SRS 2and then SDA 1.2 TL. I started looking into this, but it got over my head and had too many other projects going on to dig deeper. Adjusting the crossover of the SDA 2.3 to the 1.2 make me think using the 198's in the SRS 2 might be possible.

    On a related SDA 2.3 vs 1.2 note, I have thought about how to make a shorter SDA 1.2, roughly 2.3 height, but deeper or wider cabinet. I love the slightly fuller sound of the 1.2's, but IMO the tweeter array is too high when sitting.
  • F1nut
    F1nut Posts: 49,708
    but IMO the tweeter array is too high when sitting.
    I agree and that is why I have the 2.3TL.
    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

  • xschop
    xschop Posts: 4,636
    pkquat wrote: »
    On a related SDA 2.3 vs 1.2 note, I have thought about how to make a shorter SDA 1.2, roughly 2.3 height, but deeper or wider cabinet. I love the slightly fuller sound of the 1.2's, but IMO the tweeter array is too high when sitting.


    Good to see I wasn't the only one pondering this...
    Don't take experimental gene therapies from known eugenicists.
  • motorstereo
    motorstereo Posts: 2,042
    [quote="pkquat;c-2665128

    On a related SDA 2.3 vs 1.2 note, I have thought about how to make a shorter SDA 1.2, roughly 2.3 height, but deeper or wider cabinet. I love the slightly fuller sound of the 1.2's, but IMO the tweeter array is too high when sitting. [/quote]

    Rather than reinvent the wheel perhaps adjust the rake angle slightly......tilt them forward?

  • Viking64
    Viking64 Posts: 6,646
    It's my understanding that with the TLs, the top tweeters always produce sound, and with the "progressive array", the second, then third tweeters (and 4th on the 1.2s) produce sound as volume increases.

    Would changing the order of the tweeters via the wiring harness from bottom-to-top as opposed to the factory top-to-bottom help eliminate the problem of the tweeter array being too high on the 1.2s, or would it do more harm than good?
  • F1nut
    F1nut Posts: 49,708
    On the 1.2TL the second tweeter from the top is full blast.
    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