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

decato

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

schwarcw

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!

DarqueKnight

Excellent writeup Brian. What effects on bass response do you expect from installing a 1.2TL crossover in a smaller cabinet?

decato

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

DarqueKnight wrote:

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

You've got my wheels spinning.

Toka78

Great work, Brian! Who said the SDA was dead?

RichCanDo

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!

DarqueKnight

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.

Polk65

Excellent post Brian.

Here's some nude cousin's.

Steve

george daniel

Great post,,got me thinking about my brothers 2.3 tl's :cool:

Another cousin from the deep south

decato

I have updated the diagrams for the TL series. The tweeter polarity is now reversed, just as it is in the schematics.

Larry Chanin

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

Larry Chanin wrote:

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.

neil3305

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

Those were Gimpods boards, which are no longer produced

We do have someone who rebuilds crossovers

@VR3

F1nut

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.

txcoastal1

@F1nut ...Jesse your a slacker

BlueFox

...

JayCee

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.

Toolfan66

I joined in 09 as well, and I have never seen this thread..

decato

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

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.

JayCee

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.

decato

JayCee wrote: »

"Fine" as in very good or meh, they don't suck?

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

pkquat

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

but IMO the tweeter array is too high when sitting.

I agree and that is why I have the 2.3TL.

xschop

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...

motorstereo

[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

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

On the 1.2TL the second tweeter from the top is full blast.