Question SDA-1B

westmassguy

I recently upgraded my 2As to TL status, and they sound awesome. There's a lengthy thread on it. Some said it couldn't be done while other said it could, but no one had done it and reported back other than myself. The Hi-Pass of the 2A is identical to the 2B with the exception of a 2.7 ohm resistor in series with the shunt coil. The 2.7 ohm resistor is used to balance the output of the stereo and dimensional woofers to the tweeter out put. The 2As needed it, the 2Bs did not due to the different woofers being used in the 2B.

I'm now looking at doing the same thing with the 1Bs. The layout of the Hi-Pass section is essentially identical to the 2As (same generation) up to the point where the circuit splits for the two tweeters. I'm thinking the 5.8uf Capacitor installed accross the resistor would have the same effect for the 1B as it does for the 2A. Everything down-stream would remain the same. Any thoughts on this would be appreciated.

Schurkey

That is correct. There have been several threads discussing exactly that change to the crossover. The "best" is hundreds of posts long, and the first half is mostly conjecture, assumptions, and argument. The second half is golden. Short story: Remove 4.4uF cap, replace with 5.8uF cap. Delete polyswitch. Maybe revise resistor value.

http://www.polkaudio.com/forums/showthread.php?74946-SDA-SRS-2-Crossover-Parts-list&highlight=parts+list

Member "inspiredsports" with assistance from Matthew Himself, and several others, did all the heavy lifting. I rode along on his coat-tails and did the same thing to my 1Bs; except I only used the RD0-198s in the main tweeter positions, leaving the SL2000 in the secondary positions. (I can't stand to buy more from the Communists than absolutely necessary.)


Despite the successful transplant of the 198s in to the 1B and the electrically-equivalent SDA SRS 2 blade/blade speakers, there are still some here who "object" to this mod based (in part) on the 1B and SRS 2 B/B using two tweeters; they believe that the second tweeter isn't properly compensated by the 5.8uF (5.6uF is much easier to source, and within 5%) capacitor. I'm not an electrical engineer, I can't verify that the mathematics works out. I just know that the treble sounds fine (but with not enough volume)

The thread link above ALSO discusses changing the main resistor (2 ohm in 1B, 3.5 ohm in SRS 2 B/B) in the HF circuit to better-balance (increase the volume of) the treble compared to the mid-bass level. I suspect that a 1.5 or 1.75 ohm resistor is the solution for both speakers--your ears and listening room may say differently. Buy a batch of resistors, listen for yourself.

westmassguy

Schurkey wrote: »

That is correct. There have been several threads discussing exactly that change to the crossover. The "best" is hundreds of posts long, and the first half is mostly conjecture, assumptions, and argument. The second half is golden. Short story: Remove 4.4uF cap, replace with 5.8uF cap. Delete polyswitch. Maybe revise resistor value.

http://www.polkaudio.com/forums/showthread.php?74946-SDA-SRS-2-Crossover-Parts-list&highlight=parts+list

Member "inspiredsports" with assistance from Matthew Himself, and several others, did all the heavy lifting. I rode along on his coat-tails and did the same thing to my 1Bs; except I only used the RD0-198s in the main tweeter positions, leaving the SL2000 in the secondary positions. (I can't stand to buy more from the Communists than absolutely necessary.)


Despite the successful transplant of the 198s in to the 1B and the electrically-equivalent SDA SRS 2 blade/blade speakers, there are still some here who "object" to this mod based (in part) on the 1B and SRS 2 B/B using two tweeters; they believe that the second tweeter isn't properly compensated by the 5.8uF (5.6uF is much easier to source, and within 5%) capacitor. I'm not an electrical engineer, I can't verify that the mathematics works out. I just know that the treble sounds fine (but with not enough volume)

The thread link above ALSO discusses changing the main resistor (2 ohm in 1B, 3.5 ohm in SRS 2 B/B) in the HF circuit to better-balance (increase the volume of) the treble compared to the mid-bass level. I suspect that a 1.5 or 1.75 ohm resistor is the solution for both speakers--your ears and listening room may say differently. Buy a batch of resistors, listen for yourself.

Thanks, I cououldn't find anything specific to the 1B

bigaltx24

I put RDO-198s in my 1Bs about six months back. At first they were pretty hot on the high end but they have settled in nice. To me the 2 ohm resistor seems real close, I may experiment with it sometime in the future, but right now I'm real happy with how they sound.

westmassguy

bigaltx24 wrote: »

I put RDO-198s in my 1Bs about six months back. At first they were pretty hot on the high end but they have settled in nice. To me the 2 ohm resistor seems real close, I may experiment with it sometime in the future, but right now I'm real happy with how they sound.

You replaced the 4.4uf with the 5.8uf as well?

F1nut

Has anyone fed these altered values into a program to see what the actual frequency plots look like?

westmassguy

F1nut wrote: »

Has anyone fed these altered values into a program to see what the actual frequency plots look like?

Excellent question.

Mr. Bubbles

^^^^^^^ +1

PolkieMan

Remember the old speakers in the seventies has a dial/knob increase/decrease for high frequency I guess that was variable resistor

bigaltx24

I used a 5.6uf.

Schurkey

F1nut wrote: »

Has anyone fed these altered values into a program to see what the actual frequency plots look like?

Does anyone have accurate specs for the drivers involved? Far as I know, the driver specs (the ones actually needed for accurate frequency-response interpolation) are not available from Polk.

FIRST we'd have to analyze the tweeters. Easy enough...for someone having the appropriate background and equipment. That would NOT be me.

westmassguy

Schurkey wrote: »

Does anyone have accurate specs for the drivers involved? Far as I know, the driver specs (the ones actually needed for accurate frequency-response interpolation) are not available from Polk.

FIRST we'd have to analyze the tweeters. Easy enough...for someone having the appropriate background and equipment. That would NOT be me.

Nor me. Looks like I opened a can of worms again.

Schurkey

westmassguy wrote: »

Nor me. Looks like I opened a can of worms again.

I wouldn't say that.

Remember the old Alka-Seltzer TV commercial from many years ago? "Try it...you'll like it!"

Doesn't taste (or sound) like worms to those of us who have DONE the upgrade to 198s in the 1B/SRS 2BB.

westmassguy

Schurkey wrote: »

I wouldn't say that.

Remember the old Alka-Seltzer TV commercial from many years ago? "Try it...you'll like it!"

Doesn't taste (or sound) like worms to those of us who have DONE the upgrade to 198s in the 1B/SRS 2BB.

It's an expression! I didn't imply that yours sounded or tasted like worms for heavens sake.
My 2As were a no brainer for the most part, since the single tweeter, 3rd generation Hi-pass circuit was nearly identical to the single tweeter, 4th generation Hi-pass circuit. I only had to add a 5.8uf cap to the existing circuit, not change the value of an existing cap feeding one tweeter, while leaving the other tweeter as is. So F1nut's point is valid.