SDA2A RDO198 Upgrade??

[ben62670]

Just making sure. No pics;)

[JPSmario]

and I do have 2 MW6510's per cabinet.

[comfortablycurt]

Hmmmm...entirely possible. Perhaps someone willing to mod their 2A's to use the RD0198-1 would be willing to let us know what happens with the resistor in and out........or we can wait for Face to quit fooling around. ;)

Try it Curt!!! If you don't feel comfortable (hehe) with soldering, I'll do it for free.

hmm...I'm thinking I might have to try this. I've been tossing around whether or not I want to upgrade to a pair of 1C's this year, or upgrade my 2A's. This is making me lean towards keeping the 2A's, and upgrading the XO's so I can use 198's. Then I can keep them, and snag a pair of 1C's sometime further down the road. Then I'll have a pair of SDA's with 194's, and a pair with 198's...just to mix things up a bit.:)

I think I'm going to start looking into what it would cost altogether to upgrade my 2A's XO's. My soldering's a bit rusty, but I should be able to manage it.:)


Either way, don't be poised waiting for results. This will still be a few months down the road.;)



What was the main purpose of switching to two different mid-woofers in the 2B's? Do they have any real clear cut advantages over the dual 6510's that the 2A's have? Better bass output or anything like that?

[Amherst]

Another pair of SDA-2a's are here. Picked them up a couple of weeks ago.

I am also willing to give the tl mod a whirl with the set. If George wants to chime in here. I am local, and would be able to provide another set for collaboration/experimentation.

Baby Frankenpolk's anyone! (Of course, this term may only have continued use with Ben's permission). ;)

[george daniel]

Which George,, me or double G?

If you are talking about me,,I'm game,, you got the caps ready to go in?;)

[Amherst]

Sorry for the confusion, yup, between exit 3+4.

Haven't ordered anything, I've been studying schematic's and tying to get a game plan going when this thread popped up.

[Disc Jockey]

In trying to understand this a little better I came across these posts by gtforme00 over at DIY audio, full URL here: http://www.diyaudio.com/forums/multi...ch-rf-7-a.html

*****
Decreasing the resistance of the inductor will have two primary effects.

1. Altering the bass response of the woofers by changing the qts of the system. Typically this effect can be summed up as: lower series resistance, leaner (some would say tighter) bass; higher series resistance, more pronounced (some would say boomier) bass. Depending on your preference for bass alignments, you may like the more damped bass provided by a decrease in series resistance.

2. Altering the acoustic output across the range of the woofer by changing the resistive attenuation. This may manifest itself as a more prominent midrange due to the increased level of the woofer with respect to the tweeter. With such a small change in resistance as you are proposing, you will likely not notice the difference.

Changing the resistance of the inductor will not have an effect on the crossover frequency, as the filter effect is not a function of resistance (fixed regardless of frequency) but of impedance (changes with frequency).

The increasing impedance of an inductor with frequency is as you probably already know, the reason an inductor functions as a low pass filter. The impedance is the sum of the resistive and reactive components of the inductor at a given frequency.

At the 2200Hz crossover frequency, the impedance of the inductor will be:

Z=R+iX (ignore the i because we are only working with one complex impedance in this equation)

R = 0.30 Ohms
X = 2*pi*Frequency*Inductance
X = 2*pi*2200*0.75E-3
X = 10.37 Ohms

Z = 10.67 Ohms at 2200Hz

If you notice, the reactance of the inductor depends solely on the inductance value and frequency, thus the crossover filter frequency will rely solely on those values as well.


AND:

Changing the resistance of the inductor will not change the tuning frequency of the box. The volume of the box and the port dimensions alone affect the box tuning frequency. Changing the resistance of the inductor will however affect the woofer characteristics and thus the woofer response in a box. In this respect alone it will change the "alignment" of the driver, port, and cabinet. The changes will be what I described to you earlier.

Let me try to explain further how the series resistance effects the woofer response in a box.

When you look at thiele-small parameters of a woofer, you will see several "q" parameters. These each indicate the tendency of a woofer to resonate at its natural frequency. The higher the q, the more tendency the woofer has to resonate at that frequency. There are mechanical and electrical parameters that contribute to this tendency, but the two parameters(qms and qes respectively) are combined in the "qts" parameter, which indicates the overall tendency of the woofer to resonate at its natural frequency.

If we put a woofer in a box, the woofer mechanical suspension will combine with the tendency of the air in the box to act as a spring, resulting in a new resonant frequency and new tendency to resonate. Lets call this tendency the total system q, or "qtc".

Now, because qtc is a function of qts, which is in turn a function of qes, any changes to qes will be translated down to qtc, or simply speaking; any changes in the electrical tendency to resonate will be propagated down to the tendency of the overall system to resonate. This is where altering the series resistance comes in. By changing the series resistance to a lower resistance, we are reducing the tendency of the woofer to resonate, thus lowing the total system tendency of the woofer to resonate. This can be subjectively described as leaner bass.

The ported part of the enclosure responds to the woofers tendency to resonate. The woofer simply excites the air volume which by virtue of the port has its own tendency to resonate. Thus, lowering the tendency of the woofer to resonate by lowering the series resistance will also lower the tendency of the air mass to resonate, but will not affect the fundamental frequency at which it will tend to resonate.
*****

So it appears my reasoning was way off. :o However, I would still leave the resistor in place because of the reasons given above. As F1nut said, maybe Face will quit fooling around and give us the answers we so richly deserve. Or perhaps our new mystery mod may be the esteemed Mr. Swauger himself; he could certainly put this issue to rest.

[Amherst]

Which George,, me or double G?

If you are talking about me,,I'm game,, you got the caps ready to go in?;)

Man, I do have the G's mixed here! Apologies go out to GD and GG.

Okay,....extends face forward.....,let the slapping begin.
Uggh,....pulls face back, wipes tear away.....Wow.

Anyhow, peoples interested in get together experimenting with the SDA-2a's are more than welcome here. Next step for me seems to be to put a viable parts list together and order.

Edit:Need to wait and listen... more info coming???

[inspiredsports]

hmm...I'm thinking I might have to try this. I've been tossing around whether or not I want to upgrade to a pair of 1C's this year, or upgrade my 2A's. This is making me lean towards keeping the 2A's, and upgrading the XO's so I can use 198's. Then I can keep them, and snag a pair of 1C's sometime further down the road. Then I'll have a pair of SDA's with 194's, and a pair with 198's...just to mix things up a bit.:)

I think I'm going to start looking into what it would cost altogether to upgrade my 2A's XO's. My soldering's a bit rusty, but I should be able to manage it.:)


Either way, don't be poised waiting for results. This will still be a few months down the road.;)



What was the main purpose of switching to two different mid-woofers in the 2B's? Do they have any real clear cut advantages over the dual 6510's that the 2A's have? Better bass output or anything like that?

I tried to determine the difference when I was TL'ing my SDA SRS 2's and the closest I came to determining that info was post #22 at http://www.polkaudio.com/forums/show...ghlight=MW6509

I do have my original 1987 instruction manual for the SDA 2A with a separate "Addendum" that contains the specs for the newer 2B. Strangely (as I thought the 2B's were easier to drive) the manuals list the 2A "D.C. Resistance" as 5 ohms and the "Impedance" for the 2B as "Greater than 4 ohms"

What is certain is the mid/bass section of the 2 crossovers is vastly different with the 2B using the more modern 20 uf and 40 uf cap values, and the 2A using 2 20 uf's and 2 giant 130uf's.

[JohnLocke88]

I am very curious to see how this works out. I just found out the pair of CRS+ I picked up a while ago are the 1986 B/B version (thus, they have the same crossovers as the 2A's).

[heiney9]

What was the main purpose of switching to two different mid-woofers in the 2B's? Do they have any real clear cut advantages over the dual 6510's that the 2A's have? Better bass output or anything like that?

As time progressed the MW drivers were improved, hence one of the reason's to always get the later model SDA's if possible as well as X-overs and the actual frequency which the dim drivers operated was changed.

Drivers in the 1C's, 2B's, SRS and later used a driver with side wound voice coils, which supposedly were an improvement. X-overs were simplified and driver impedance was changed, etc. The entire SDA properties were refined in later models............all reasons why different drivers were utilized.

H9

[chandler9a]

I am very curious to see how this all works out as well. I thought I would leave well enough alone but it seems like that option doesn't last long with people like us;).

I would be up for experimenting as well.

[JPSmario]

I've been listening to the RDO194's for about a week now and I won't be going back to the SL2000's. The ear fatigue problem is virtually gone and the SDA's seem to sound better every day as I work my way through my music. I'm also hearing the warmup effect now that I never noticed before with the my old B&W 602's. 30 minutes ofcooking smooths things out and expands the stage significantly. I'm looking forward to hearing how 2A x-over upgrades go for other folks; unfortunetely, it's not in my near-term budget. Thanks, guys!

[comfortablycurt]

Awesome!! Good to hear the tunes are great on your end.

I've been jamming out with my 194'd 2A's all day. They sound fantastic.:)


I still can't wait to mod them and TL them though.

[JPSmario]

this weekend I put in the Dynamat and Mortite and wow :D seems like the speakers are re-voiced! while the bass now seems to erupt from the floor and the walls, the mid's and highs just sparkle! I know, a lot of exclamation marks, but who knew $25 could do so much? now I have to go through my music again, tough job, but somebody has to do it ;)

[inspiredsports]

Great work, and don't forget you can add the 5.8 bypass and RDO-198's in the future if you should be so inclined

[Rev. Hayes]

Did anyone actually do this????

If so could you point me to the thread that describes the process and results?




Edit: I'm referring to the SDA-2A TL upgrade that was discussed above.

[Rev. Hayes]

Did it happen or not??????

If so please PM me I would like to chat.

[comfortablycurt]

I'm planning on trying it soon. I'm hoping I can get around to completely rebuilding my 2A's over the winter. I'm planning on doing full XO mods first, then once I've got the new XO's broken in and I've gotten some good listening time in, I'll mod the XO's again and swap in some 198's. I've been slowly accumulating all the parts that I'm going to need...I've got about half of the parts together now. I won't have the time to get around to it for another couple months or so though.

I'm definitely looking forward to finding out how they turn out. As far as I know, nobody has TL'd a pair of 2A's yet.

[chandler9a]

This sounds great Curt. I can't wait to hear your impressions of them after they are done. I plan on doing my 2As at some point as well but its hard to convince myself to do it since I really like the way they sound now.

Either way, I'm sure it will be worth it in the end.

Good Luck!!

[JPSmario]

This sounds great Curt. I can't wait to hear your impressions of them after they are done. I plan on doing my 2As at some point as well but its hard to convince myself to do it since I really like the way they sound now.

Either way, I'm sure it will be worth it in the end.

Good Luck!!

+1

I'm planning on trying it soon. I'm hoping I can get around to completely rebuilding my 2A's over the winter. I'm planning on doing full XO mods first, then once I've got the new XO's broken in and I've gotten some good listening time in, I'll mod the XO's again and swap in some 198's. I've been slowly accumulating all the parts that I'm going to need...I've got about half of the parts together now. I won't have the time to get around to it for another couple months or so though.

I'm definitely looking forward to finding out how they turn out. As far as I know, nobody has TL'd a pair of 2A's yet.

My plan matches Curt's; I'll get the XO's done this winter and get lots of listening in after they burn in. then I'll swap out the 194's for the 198's and try with the resistor in place before removing it.

But I also have to agree with chandler9a. I haven't been in a hurry for the next mod's because I'm loving the way they sound now. It's almost a PATA; it's hard to get anything done while the music is on because I just want to sit and listen!

[frickingruvin]

As time progressed the MW drivers were improved, hence one of the reason's to always get the later model SDA's if possible as well as X-overs and the actual frequency which the dim drivers operated was changed.

Drivers in the 1C's, 2B's, SRS and later used a driver with side wound voice coils, which supposedly were an improvement. X-overs were simplified and driver impedance was changed, etc. The entire SDA properties were refined in later models............all reasons why different drivers were utilized.

H9

First of all...Thanks for all the responses!
H9: Regarding your reply quoted, does that mena that the recapping of the later model crossover takes different caps?
Thanks for the input on the Dynamt and Mortite....I'll have to invest in those products while I am in there...
I'll still perform the 194/crossover recap. Maybe at some time later I will make the TL mod...

Is there a thread on actually doing the 194/recap? I have been searching, but haven't came across one yet

[Smallies]

Don't forget to break out the needlenose and extract those blade blade inputs and throw them in the trash.They are sealed with glue on the inside of the cabinet.

[TennMan]

...I'll still perform the 194/crossover recap. Maybe at some time later I will make the TL mod...

The TL mod is based on using the RDO 198 tweeter and wouldn't work correctly with the RDO 194 tweeter. You should decide whether or not you want to do the TL mod before purchasing new tweeters.

[westmassguy]

I'm resurrecting this thread to find out if anyone has actually done the "TL" Mod on their 2As. I've done pretty much every upgrade on my 2As, except this one. Quite a few have said it should work, but no one seems to have reported back that it did work.

[westmassguy]

Well, looks like I'm going to have to be my own guinea pig on this one. Ordered the caps and tweets today.

[doctorolds]

Well, looks like I'm going to have to be my own guinea pig on this one. Ordered the caps and tweets today.

That is great. Please post your comments once you get it completed. I picked up a pair of SDA 2A's a few weeks ago and I am also curious about the upgrade. Good luck!

[westmassguy]

That is great. Please post your comments once you get it completed. I picked up a pair of SDA 2A's a few weeks ago and I am also curious about the upgrade. Good luck!

I'll post my results here, and my other thread: http://www.polkaudio.com/forums/show...ished...Almost

[deronb1]

This is very interesting. Was just wondering how much of an ordeal it would be to go "TL" on my 2Bs. If it is just a matter of swapping some caps, it may be something I can handle.

[pitdogg2]

This is very interesting. Was just wondering how much of an ordeal it would be to go "TL" on my 2Bs. If it is just a matter of swapping some caps, it may be something I can handle.

It is well documented here and that is all it is. The CRS+ and the 2B use the same board so plenty is here.