What do I have SRS, 1.2 or 1.2TL????

Beachmover · October 27

Forgive the dumb question and hopefully this is posted in the correct spot. I've been looking for a set of these locally for a long time and one popped up for an incredible price and had to jump on it. They are definitely not in the best shape and have been messed with at some point.

Unfortunately, I am at a loss as to what model they are, the label on the back was removed.

-They both have the 1.2 or 1.2TL crossover plate with the single bolt but not sure as to which crossover is installed.
-Both have the pin and flat cable connector
-Both have the S2000 tweeters
-One has a solid oak top cap and the other is a veneered oak top cap.
-One box is full of 6510 and the other 6511 drivers.

Any help or other features to look out for to figure out what Frankenstein speakers these are would be greatly appreciated. Would like to ultimately restore them and keep them for the long term.

xschop · October 27

They are hybrids awaiting more hybridization.

Beachmover · October 27

Do you have any suggestions as to where to go from here?

xschop · October 27

Is there a part# located on the Xovers?

Gardenstater · October 27

With those SL2000 tweeters and that manufacturing date they would have to be 1.2. 1.2tl had the SL3000 and came out in 1989. They are not supposed to have MW6510; they should have MW6511 for the SDA drivers and MW6503 for the stereo drivers.

xschop · October 27

Should be easy to "TL" them with the earlier crossovers since you have the 6510s already.

What passive radiators do they have?

https://forum.polkaudio.com/discussion/37333/sda-srs-1-2tl-crossover-upgrade

Gardenstater · October 27

What is the bolt configuration on the crossover plates? You said they have the single bolt? It sounds like you have the 1.2tl configuration if you have four bolts across the top, four bolts across the bottom, and a single bolt in the center. The crossover for the 1.2 is #BE2000-B and the 1.2tl is #BE2000-C

Also, the MW6510 has pretty similar Thiele/Small Parameters to the MW6503 and maybe someone swapped those in for the original MW6503. They are supposed to be on the inside edges of the speakers. You should install them that way and make sure they are wired to the stereo part of the circuit boards.

Beachmover · October 27

Thanks for all of the help.
Here are some more photos to help identify these. Was Polk still making these in Baltimore in 88? Only thing I could think of this is a hodgepodge of parts put together by an employee since I picked these up a few blocks from the original location.

Gardenstater · October 27

According to the SDA Handbook, the Fifth Generation SDA models were made from 1989 to 1991.

Polk was at 5601 Metro Drive, Baltimore. Md. 21215 in 1988 and 1991.

If that was done by an employee he must've been trying to sabotage the Polk reputation by putting all 6510s in one cabinet, which is about 8 ohm impedance and all 6511s in the other cabinet, which is about 4 ohm impedance. It's all wrong. Most likely someone chimped them up between then and now.

Looking at the values of capacitors, at least the ones visible, you have the 1.2 boards.

Gardenstater · October 27

Blue +/Green - are the wires to the SDA Drivers (MW6511) and Black +/White - are the wires to the Stereo Drivers (MW6503 or in your case MW6510).

Beachmover · October 27

Awesome. I was just going to ask that. Thank you for all of the information. Can't wait to get these cleaned up and set up like they should be.

Gardenstater · October 27

They don't show it in the 1.2 Schematic but they are hooked up in Series/Parallel as shown in this screenshot from the SRS Schematic:

Link to your schematic 1.2:

https://us.v-cdn.net/5021930/uploads/attachments/1/8/5/1/1/26686.pdf

Tweeters are numbered 1 to 4 with 1 at the top. I'd check them to make sure someone didn't mess them up too. Assuming the wiring is the same as the 1.2tl:

T1: Red (+), White (-)
T2: Blue (+), White (-)
T3: Yellow (+), White (-)
T4: Green (+), White (-)

If it isn't the same as the 1.2tl hopefully someone else will chime in.

michaeljhsda2 · October 27

Gardenstater wrote: »

With those SL2000 tweeters....they would have to be 1.2. 1.2tl had the SL3000.

Exactly right, no doubt about it. Pin/blade interconnect socket excludes them from being 1st gen. SRS.

Beachmover · October 27

It makes sense now. I was thrown off by the drivers and solid wood end caps.
Everything I read was the 1.2 had the 6503 drivers and laminated end caps.

Already started dynamatting the drivers using what I had left from the RTA12.

Does anyone know what kind and how much fill or cabinet lining went into these?

michaeljhsda2 · October 27

Beachmover wrote: »

Does anyone know what kind and how much fill or cabinet lining went into these?

There's not any in there?! There are 2 columns in each cabinet. Each column of dacron starts at the top of the cabinet and extends to the bottom mid-woofers.

Beachmover · October 27

Completely empty.

Gardenstater · October 28

Is there a picture of the guy you bought these from in the Post Office 🤣?!

Beachmover · October 28

These were buried in a back corner of a dirty garage full of junk and engines. I knew they were far from mint and would require a lot of work. They have definitely been messed with over the years but at least it all seems fixable. All the drivers still function and none of the magnets have shifted, only need to replace one of the surrounds.
For $300 though I can't complain.

xschop · October 28

At least they didn't paint them Acid Trip Red.

Gardenstater · October 28

And you are already dynamatting them. Kudos. I heard a rumor there was a guy who used to haunt this forum who owned them for 10 years or so and never did that.

ptrooper · October 28

Beachmover wrote: »

Thanks for all of the help.
Here are some more photos to help identify these. Was Polk still making these in Baltimore in 88? Only thing I could think of this is a hodgepodge of parts put together by an employee since I picked these up a few blocks from the original location.

Excellent score Gratz

These look identicle to my 1.2's , I have only removed the top tweet bezel and front to rear measured 273mm.

Please take more internal pics of bracings for future reference.

The internal grooving. Their engineered purpose is to increase rigidity, reduce panel resonance, and break up internal standing waves. This is not inside the original SDA SRS'S

Always a buz to see another set captured to be tamed

Beachmover · October 28

Finally had the time to take all of the drivers out.
These had (5) 6510 and (11) 6511. Could be worse I guess. Does anyone have a suggestion on what to do for the missing 3 stereo speakers other than keep an eye out on the bay? Do any other Polk models use those drivers?

xschop · October 28

Those extra 6511's will come in handy later.

Gardenstater · October 29

Beachmover wrote: »

Finally had the time to take all of the drivers out.
These had (5) 6510 and (11) 6511. Could be worse I guess. Does anyone have a suggestion on what to do for the missing 3 stereo speakers other than keep an eye out on the bay? Do any other Polk models use those drivers?

I believe the vintage RTA series used them (MW6510), although perhaps not in every revision. RTA 8t, RTA 11t, RTA 15t. Also SDA CRS+.

If you get lucky and those come up for sale inexpensively, or someone parts them out on eBay you will be good.

Hard to know what is the best path forward. Getting 8 MW6503 would be pretty unlikely short term. They are definitely different. Unfortunately we don't know official Polk data for Qts for the MW6510 and that is one of the most critical parameters and that makes it hard to compare the two. I think maybe DarqueKnight may have measured that with DATS. I'll try to find the thread. This thread is interesting but people seemed to not know that they were talking about Qms, not Qts. Qts = (Qms x Qes)/(Qms + Qts).

Some reading:

https://forum.polkaudio.com/discussion/50111/difference-between-mw-6510-and-mw-6503-drivers

https://forum.polkaudio.com/discussion/133992/thiele-small-parameters-for-mw6500-drivers#latest

https://iwistao.com/blogs/iwistao/understanding-key-loudspeaker-parameters4-total-q-factor-qts-the-balance-between-damping-and-efficiency?srsltid=AYCX9vI-E2PahpbzL777tWZq4sRqg20MS_yMQx6-JlrtK9_SeKvoOPNp

PS: Another possible option is to get your hands on 4 MW6503 and combine equal numbers of MW6503 and MW6510 in each cabinet's Series/Parallel configuration so that it is two groups of MW6503 in series with MW6510 that are in parallel with each other.

You could luck into a pair of M10 or early CRS that get parted out or that get sold whole on EBay.

xschop · October 29

Early RTA-8 are all 6510's. The later 8TLs were all 6516's. IIRC all 11T/TLs are all 6510's.

Gardenstater · October 29

I found DarqueKnight's DATS measurement of his original MW6510 in the left CRS+ he owned. Q's are very similar to MW6503 specs provided by Polk, but you never know how much different measuring setups could be a factor and unless he posted his DATS measurements of an MW6503 somewhere to compare to, we are in doubt. His Qms of 1.867 is grossly different from Polk's 1.390, for example. Fs that he measured is 6 Hz higher than Polk's specs as well.

https://forum.polkaudio.com/discussion/197520/crs-1989-driver-phase-plug-and-aluminum-tweeter-plate-modifications#latest

xschop · October 29

The higher Qms explains the aging and obvious usage of a 35-40 year old driver. That's why you shouldn't fret over a 6503 vs. 6510 IMO.

His 6511's he sent me were EOSL.

Beachmover · October 29

Thanks again for all of the information. I feel lost with these speakers, It seems like Polk was all over the place back then.
I have the option to pick up a pair of Monitor 12s Series 2 for $300, this would get me 8 6503s to replace all of the 6510s.
Or should I wait to find some original 6510s?
Also, how do the Midwest Speakers compare to the original Polks? Would replacing those 3 missing 6510s with the new ones be a huge difference?

If you can't tell I am antsy to get these up and running.

Gardenstater · October 29

xschop wrote: »

The higher Qms explains the aging and obvious usage of a 35-40 year old driver. That's why you shouldn't fret over a 6503 vs. 6510 IMO.

His 6511's he sent me were EOSL.

Exactly! In our vintage speakers we probably have all sorts of mismatched drivers now due to different aging and usage. Qms would definitely rise as the suspension wears out over time. Spider and Surround both get softer and more compliant.

https://speakerwizard.co.uk/qms-mechanical-quality-factor/

https://iwistao.com/blogs/iwistao/understanding-key-loudspeaker-parameters11-mechanical-q-factor-qms-how-suspension-controls-motion?srsltid=AYCX9vIbGNH_hLJgbVquscfJ0lQ0cwaYoD_BEYegXEoucAWr4GIqjzuH

https://iwistao.com/blogs/iwistao/understanding-key-loudspeaker-parameters13-mechanical-compliance-cms-in-loudspeakers?srsltid=AYCX9vLRHnYPy0JCKRDmeACrHf5tlujbIZzQdNglE2NoG2rTooeGrEvy

Gardenstater · October 29

Beachmover wrote: »

Thanks again for all of the information. I feel lost with these speakers, It seems like Polk was all over the place back then.
I have the option to pick up a pair of Monitor 12s Series 2 for $300, this would get me 8 6503s to replace all of the 6510s.
Or should I wait to find some original 6510s?
Also, how do the Midwest Speakers compare to the original Polks? Would replacing those 3 missing 6510s with the new ones be a huge difference?

If you can't tell I am antsy to get these up and running.

I would jump on those M12. If any are locked or rubbing ask for some $ off that price. That would even let you load up one cabinet with the MW6503 and the other with MW6510 and see if you hear the difference. Remember, the MW6510 were NOT the original drivers as far as I have been able to determine. Page 12 of the SDA Handbook:

xschop · October 29

I've dissected enough 6510's and 6511's. The only difference between them is the extra coil winding of the 6510's. Same flabby suspension/thin spiders as the 6511's.

At this point, get whatever you can get 6503/6510 used or repro. The repro will obviously have a tighter suspension, but should match close as possible to orig. DCR

What do I have SRS, 1.2 or 1.2TL????

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