I would like to "TL" my 1986 SDA SRS 2's

inspiredsports

In my 1986 SDA SRS 2's, I've recently replaced the original SL2000's with RDO 194's and had my crossovers rebuilt. This is a 4 ohm system. After 500 hours, the sound is very, very good, but I've also completed the "TL" upgrade to my 2B's where the (I think superior) RDO198-1 is used. I personally prefer the sound qualities of the RDO198-1's.

I studied the "SDA SRS 2 1986" and "SDA 1B" schematics in DarqueKnights portion of the Sticky at http://www.polkaudio.com/forums/showthread.php?t=55888 and learned these 2 crossovers are the same, with the slight exception of a single 2.0 ohm resistor in the tweeter circuit on the 1B that is a 3.5 ohm on the SRS 2.

I bought a pair of the 1B crossovers I found on eBay, and since they will be replaced, the different resistor doesn't even matter. I don't believe it's ever been done, but I now have the raw material to work with to make a "TL" VERSION OF THE 1986 SDA SRS 2 CROSSOVER.

What I don't have is the electronics knowledge necessary to know what values need to be changed and what additional components need to be inserted into the circuitry to accommodate the the higher impedance that 2- RDO198-1's will introduce to the circuit.

Does anyone in the group have any idea where to start? / who to contact?

Face

It appears some TL series crossovers have a contour curve, and some don't. So I don't believe it's a quick or easy adjustment for someone like you or I. It would be nice though, I agree about the 198 sounding much better.

zingo

I'll pull up the schematics and get back to you.

zingo

Well...

The CRS+ mod plugs in a 5.8uF cap onto the 2.7 ohm resistor in the tweeter circuit. That's the only change in that x-over to swap out the tweeters. You could try that as a place to start if it is possible. (This would be a REAL over simplification)

hearingimpared

Lasareath wrote: »

But maybe I'd like to go one step further and make it so that the SRS 2's could use the AI-1 cable as well.

Sal

Sal are you planning on using a non-common ground amp on your 2s?

Systems

inspiredsports wrote: »

Does anyone in the group have any idea where to start?

That won't be a simple fix.Besides the change in impedance there may also be sensitivity and frequency response differences between the 198 and 194.In all likelihood every component in the hipass section would have to have its value adjusted to get the intended response.Without the ability to make accurate measurements and the aid of some speaker optimization software you are shooting in the dark.

F1nut

In all likelihood every component in the high pass section would have to have its value adjusted to get the intended response.

Bingo!

inspiredsports

I've been studying a stack of related Polk schematics for a day now and it looks like there is no easy to follow template as the original TL models are all more complex arrangements.

Sal is right on the money that the 2B is a simpler upgrade due to its single tweeter design.

It looks like it will be an involved project to come up with the component list. With that said, I'm going to see if I can pick up some hints about theory and equipment needed, and start tinkering.

inspiredsports

Well, I'm "getting a drink with a fire hose" learning about this stuff. It's somewhat above my head but I'm taking one step at a time and wading through it.

I found an extremely in-depth article about crossover design that may help me (and others) in attempts to build or modify crossovers:

http://sound.westhost.com/lr-passive.htm

inspiredsports

I'm looking at schematics for the 2.3 TL and 1.3 TL to see if there are any apparent hints. I don't think any of the TL'd speakers that were produced by Polk used a two tweeter design like the SDA SRS 2 or SDA-1B.

I think calculating the proper values of capacitors, resistors and inductors to match the RDO198-1 impedance versus frequency response is going to require taking physical measurements of the RDO's output and running the spreadsheet in that link I referenced above.

jcaut

inspiredsports wrote: »

I think calculating the proper values of capacitors, resistors and inductors to match the RDO198-1 impedance versus frequency response is going to require taking physical measurements of the RDO's output and running the spreadsheet in that link I referenced above.

It'd take more than that, acutally. People tend to think of the crossover and the driver as a simple system-- as if you can just match up the crossover that "goes with" the tweeter. It might work that way if you were only talking about a driver with a crossover-- but when you're working with multiple
drivers on a baffle, in an enclosure,.. all that has to be taken into account. Diffraction effects, phase relationships, etc., etc. There's a lot going on there, especially in those speakers. You would need accurate measurements and the ability to model changes in software, because you'd probably end up redesigning the entire high pass section. My guess is that the changes required wouldn't be drastic, because I don't think there's that much difference between those two tweeters. But little changes can make a big difference when you look at the system as a whole.

inspiredsports

I don't have a compendium. Can anyone provide me with the impedance values for:

SL2000
SL3000

MW6501
MW6503
MW6509
MW6510
MW6511
MW6513

On a related note in trying to learn how Polk designers set some of values, I'm studying the the Schematics of the SDA-1B and SDA SRS 2. They used IDENTICAL components except the smaller volume 1B had a 12" SW120 and the larger SRS 2 use the 15" SW150.

There is only 1 difference in the entire crossover network. I'm perplexed that the high pass on the 1B used a 2.0 ohm resistor as the first component in the + side to the tweeters where the SRS 2 used a 3.5 ohm in the exact same spot.

Am I wrong in thinking is should be the same since all powered drivers are the same, or even though it is in the high-pass, is it related to the different passive radiator?

jcaut

If you want to dig deeper and don't want to spend much money, Speakerworkshop is free and the crossover modeling is quite good. You need some additional hardware to take measurements though.

inspiredsports

jcaut wrote: »

. . . little changes can make a big difference when you look at the system as a whole.

I think that must be what is going on in my 2.0 ohm versus 3.5 ohm observation at the bottom of my post #15

inspiredsports

jcaut wrote: »

If you want to dig deeper and don't want to spend much money, Speakerworkshop is free and the crossover modeling is quite good. You need some additional hardware to take measurements though.

Thanks for this link. "You're never to old to learn", they say. Now's about the time I wish I'd followed my Father's footsteps into engineering rather than business.

inspiredsports

Lasareath wrote: »

I looked through my Compendium and I can't find any impedance values.

I guess the nominal values for the actual speaker systems must tell it so the info I should have asked for is impedance of:

SDA-2B
SDA-1B
SDA SRS 2
SDA SRS 2.3
SDA SRS 2.3TL
SDA 3.1 TL

BigMac

I am not familiar with any of this but I have this info. I ran across some time ago. I have a whole disc of Polk info. around here somewhere in all these discs. If I run across it I will post all the info. I have. Hope there is something in here that you can use.

Driver: MW 6500 Driver's model #.
Brand: Polk Driver's brand name.
Fs: 31.0000 Hz (Free air resonance)
Vas: 2.6486 ft^3 (Compliance volume)
Qts: 0.2190 Total Q
Qms: 1.3000 Mechanical Q
Qes: 0.2640 Electrical Q
Sd: 0.0130 M^2 (Piston area)
Xmax: 3.1800 mm (Cone excursion, linear)
Revc: 6.5000 ohms (DC resistance)
Znom: 8.0000 ohms (Nominal impedance)
Pmax: 35.0000 watts maximum rated power


Driver: MW 6501 Driver's model #.
Brand: Polk Driver's brand name.
Fs: 31.0000 Hz (Free air resonance)
Vas: 2.7545 ft^3 (Compliance volume)
Qts: 0.2790 Total Q
Qms: 1.4700 Mechanical Q
Qes: 0.3440 Electrical Q
Sd: 0.0130 M^2 (Piston area)
Xmax: 3.1800 mm (Cone excursion, linear)
Revc: 7.7500 ohms (DC resistance)
Znom: 8.0000 ohms (Nominal impedance)
Pmax: 35.0000 watts maximum rated power


Driver: MW 6502 Driver's model #.
Brand: Polk Driver's brand name.
Fs: 44.0000 Hz (Free air resonance)
Vas: 1.2360 ft^3 (Compliance volume)
Qts: 0.2790 Total Q
Qms: 1.9700 Mechanical Q
Qes: 0.3250 Electrical Q
Sd: 0.0130 M^2 (Piston area)
Xmax: 3.1800 mm (Cone excursion, linear)
Revc: 3.5200 ohms (DC resistance)
Znom: 4.0000 ohms (Nominal impedance)
Pmax: 35.0000 watts maximum rated power


Driver: MW 6503 Driver's model #.
Brand: Polk Driver's brand name.
Fs: 29.8600 Hz (Free air resonance)
Vas: 3.0017 ft^3 (Compliance volume)
Qts: 0.3100 Total Q
Qms: 1.7680 Mechanical Q
Qes: 0.3760 Electrical Q
Sd: 0.0130 M^2 (Piston area)
Xmax: 3.1800 mm (Cone excursion, linear)
Revc: 6.5400 ohms (DC resistance)
Znom: 8.0000 ohms (Nominal impedance)

Just found this here at CP:

The MW6510 is no longer available through us and the MW6503 is the substitute. It is *close* but not an exact match. Here's some of the basic differences:

6510 vs 6503
Q 1.82 vs 1.39
BL 5.24 vs 6.62 N /AMP
Compliance 3.55E-3 vs 3.41E-3 N/M
DCR 6.54 vs 6.57 ohms
Fs 29 vs 31 Hz.
__________________
-Eric
-Polk Audio

Will keep looking around to see if I find anything else. This also helps me learn all this stuff,lol.

inspiredsports

Wow, thanks for the fast response! The 6509, 6510 and 6511 info would round it out.

inspiredsports

Lasareath wrote: »

Maybe you should just copy the 1C crossover and change out all the MW6509's and put in MW6510's & MW6511's

That's basically what happened with the 2nd generation Pin/Blade SRS 2's

The CRS+'s which can be changed to accept RD0198-1's have MW6510's & MW6511's just like the 1C's and the Second generation SRS 2's

Yes, i understand that you will be changing out all the drivers, You'll basically be making a bigger footprint SDA-1C.

This is a very good idea, but then there's still that nagging question (from the bottom of my Post #15) about why the nearly identical SDA-1B and SDA SRS 2 use one different resistor value. It must have something to do with the different cabinet sizes/different passives involved?

heiney9

A 1B isn't even remotely a "TL" version. My guess is since the cabinet and PR are larger in the SRS2's there was a different value for a different contour of the x-over for the added volume and size.

Disc Jockey

I can't help you with the resistor value question but if the crossover circuit is the same as the 1B, you should be able to do this simply. I looked in to the TL upgrade on a pair of 1Bs I ws going to buy, and this is the response I got from Ken (great CS as always):

Hello,
I forwarded your question to Matthew Polk:


"Yes, that modification should work. The 5uf cap, also known as a "By-pass cap", should only be added across the resistor that is in series with the input signal and not the one that is in series with the small inductor.

The inductance of the tweeter voice-coil causes the impedance to rise at high frequencies contributing to a gentle roll-off. The by-pass cap modification allowed us to compensate for that roll-off without disturbing the carefully tuned relationship between the tweeter and the drivers in the crossover region."

Regards, Ken, Polk Audio

inspiredsports

Disc Jockey wrote: »

I can't help you with the resistor value question but if the crossover circuit is the same as the 1B, you should be able to do this simply. I looked in to the TL upgrade on a pair of 1Bs I ws going to buy, and this is the response I got from Ken (great CS as always):

Hello,
I forwarded your question to Matthew Polk:


"Yes, that modification should work. The 5uf cap, also known as a "By-pass cap", should only be added across the resistor that is in series with the input signal and not the one that is in series with the small inductor.

The inductance of the tweeter voice-coil causes the impedance to rise at high frequencies contributing to a gentle roll-off. The by-pass cap modification allowed us to compensate for that roll-off without disturbing the carefully tuned relationship between the tweeter and the drivers in the crossover region."

Regards, Ken, Polk Audio

Wow! This sounds like exactly what we're after. Do you have a diagram or any further details for what was being discussed between you Ken and Matt when you say "that modification" ???

I believe it's a 5.8uf cap plus a 2.7 resistor when upgrading the SDA-2B (and CRS+).

As far as the 2.0 (1B) versus 3.5 (SRS 2) resistor, I would err on using the 3.5 as used in the bigger cabinet since it is the SDA SRS 2 I want to mod.

Disc Jockey

By "that modification" all I ws talking about was adding the 5uf cap in parallel with the 2.7 ohm resistor that was done on the CRS+, and whether that needed to be done to both tweeters or just one.

inspiredsports

Disc Jockey wrote: »

By "that modification" all I ws talking about was adding the 5uf cap in parallel with the 2.7 ohm resistor that was done on the CRS+, and whether that needed to be done to both tweeters or just one.

Just to be certain, I think it is a 5.8 uf cap and not a 5.0. I had Ben do my SDA-2B's and we used a Sonicap 5.8 (special valued as 5.6 is their stock value) and a 2.7 Mills Resistor. F1 and other were involved at the time and I think 5.8 is right.

Can you verify your discussion was specifically in regard to the SDA -1B ?

PS: Does anyone have the SDA-2B "TL" Schematic that was invented by the some of the Gurus a while ago ?

Disc Jockey

Yes, it is a 5.8uf cap. Srrry about that. This was definitely about the SDA 1B.

BigMac

Here is a little more info. I found. Sorry if some of this is not helpful but I am trying,lol.

http://www.polkaudio.com/forums/showthread.php?t=55888

http://www.polkaudio.com/forums/showthread.php?t=62106

http://www.polkaudio.com/forums/showthread.php?t=50115

Systems

inspiredsports wrote: »

Am I wrong in thinking is should be the same since all powered drivers are the same, or even though it is in the high-pass, is it related to the different passive radiator?

The resistor will only affect the hi pass response /treble balance it will have no affect on PR/bass tuning.

inspiredsports

GV#27 wrote: »

The resistor will only affect the hi pass response /treble balance it will have no affect on PR/bass tuning.

So I guess we can safely assume that the use of the 2.0 ohm in the SDA-1B high-pass, and use of the 3.5 ohm in the SDA SRS 2 was due to tuning the identical tweeters to the 2 different cabinet volumes.

If I'm guessing it right, the 3.5 resistance would cause more tweeter output? This theory would make sense as the larger volume cabinet would probably suck up more energy? Help!

inspiredsports

BigMac wrote: »

Here is a little more info. I found. Sorry if some of this is not helpful but I am trying,lol.

http://www.polkaudio.com/forums/showthread.php?t=55888

http://www.polkaudio.com/forums/showthread.php?t=62106

http://www.polkaudio.com/forums/showthread.php?t=50115

Very helpful and appropriate to this thread. I followed post 62106 extensively when having my SDA-2B's modded. My 2B's are a dream !!! That's SPECIFICALLY why I want to attmpt to fit the RDO198-1's into my SRS 2's. Once you heard the "TL" mod you are wreaked for life!

What I'm concerned about is that I'm not aware that anyone has ever actually done this to the SDA-1B or SDA SRS 2.

I'm looking for confirmation that we are not confusing "1B" and "2B" (knowing the 2B is absolutely capable of the TL upgrade) in Disc Jockeys posts.

Systems

inspiredsports wrote: »

So I guess we can safely assume that the use of the 2.0 ohm in the SDA-1B high-pass, and use of the 3.5 ohm in the SDA SRS 2 was due to tuning the identical tweeters to the 2 different cabinet volumes.

No the cabinet volume is part the bass tuning,the resistors value is not related to it.It only affects the tweeters response.

If I'm guessing it right, the 3.5 resistance would cause more tweeter output?

More resistance =less output.

This theory would make sense as the larger volume cabinet would probably suck up more energy? Help!

As mentioned above, the tweeters output is not related to or affected by cabinet volume because it's diaphram/dome is completey sealed.As for woofers bigger boxes =greater efficiency.

inspiredsports

Disc Jockey wrote: »

Yes, it is a 5.8uf cap. Srrry about that. This was definitely about the SDA 1B.

Did you ever go through with this mod?