A few questions on SDA-1A's

Dudeman258

Hello folks,

Well I am sorry if I am being redundant here. I have read as many threads concerning the SDA's as I can find in search. I have a few questions, that do not necessarily require allot of detail, but I really would like them answered if possible.

First, I only have a basic knowledge of RC circuits, however, when looking at the schematics, it appears a recap would only affect the mid and high level transducers. Why is it that in EVERY review, it is mentioned "bass improves significantly"? None of these reviews had new inductor coils therefore I do not see how the low freq drivers are affected?

Secondly, how is the interconnect cable used here. It is my understanding, on the SDA-1A, which uses the twin blade connection, that only one of these blades is needed correct? I have searched this, but couldn't find a definitive answer. I assume this is because only one blade is needed for the stereo dimensional driver. And since I have the tweeter disconnected, I only need the one connection to the positive side of the stereo driver?

Thank you for any and all help folks.

Walker

dorokusai

Are you sure you're no confusing the Passive Radiator with an active driver? The "recap" covers all the active drivers in the loudspeaker.

F1nut

The definitive answer, the blade/blade cable uses both wires.

Dudeman258

Ok so I am assuming each blade is the positive to either side, powering both tweeter and dimensional stereo array, that works for me.

And I am aware of the passive radiator configuration. My question pertains to the fact that the crossover schematic shows only the inductor limiting the frequencies reaching the two LF transducers. Therefore how does recapping the crossover affect LF response. What am I missing?

Walker

dorokusai

I'm not sure what schematic you're looking at but that's not the case. You may want to look closer as it's painfully obvious to me. Not sure what you mean by the positive to each side. That's not the case either as Pin A is the positive for the dimensional mid driver but Pin B is the negative for the dimensional tweeter.

Sorry, missed the second part of your question and Jesse is correct....both blades are in the circuit in regards to the SDA1.

BTW - Thanks for joining Dudeman258. We'll get you squared away and all your questions answered eventually

Dudeman258

Ok, I looked at the crossover schematic, I understand the blade connections now. I had not noticed this, as I was using the schematic for crossover capacitor information only.

Can anyone speak to my question about the crossover? Does it makes sense? I am simply asking why the bass response is noted to improve, that is it.

Thanks.

Walker

dorokusai

It's been answered. No SDA Polk speakers work with only an inductor on the LF side, period. That is it.

Every schematic involves a resistor and a capacitor for the LF side. There are only two kinds of drivers in this model, HF and LF. Even mid-level transducers produce bass.

Dudeman258

Ok, then here is where I am confused. Using the SDA-1A schematic here:

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

I am looking at the schematic, I only see capacitors and resistors for the tweeter; and a just a capacitor for the stereo driver. The bass drivers I only see a coil inductor.

I must be reading the wiring wrong then, because it looks like the wiring from the bass drivers are completely independent from the other crossover components.

Walker

dorokusai

Walker - All I can say is that you're reading it wrong. They are not independent from the rest of the crossover. Don't look at it as a solely point to point process, does that help?

Mark

Dudeman258

dorokusai wrote: »

It's been answered. No SDA Polk speakers work with only an inductor on the LF side, period. That is it.

Every schematic involves a resistor and a capacitor for the LF side. There are only two kinds of drivers in this model, HF and LF. Even mid-level transducers produce bass.

I understand the midrange technically can be considered "bass". Perhaps you yourself have not witnessed those saying very low frequencies were affected. It is not a big deal, I was simply hoping for some insight. I will be recapping my SDA's regardless.

Thank you for your patience and help.

Walker

Dudeman258

dorokusai wrote: »

Walker - All I can say is that you're reading it wrong. They are not independent from the rest of the crossover. Don't look at it as a solely point to point process, does that help?

Mark

I see. I assumed the full range technically was delivered to each branch, and each passive component then limited what could go through it. If this is true, then where am I missing that there is a direct path to the LF drivers with only the inductor in between.

Please consider post #21 on this SDA recap thread (link below). If you can describe what it is I am not taking into consideration I would feel much better.

http://www.polkaudio.com/forums/showthread.php?t=65993

Walker

Joe08867

You are almost understanding. The mid Drivers are what is creating the bass. The Passive is just that Passive. In SDA's the 6.5inch speaker is the mids and lows for the speaker system. The passive expands on what they can do but in a way like a port does in certain types of speakers but with more control.

As far as the upgrade goes. Yes the very low frequencies are affected but not in the it created new lower frequencies. It is more it created cleaner more well defined low end sound. The bass was more detailed and tighter which in turn helped with the sub-bass frequencies. It didn't create new it just makes what is there better.

Dudeman258

Ok, that helps. Although I still don't see the whole here. One more shot?

Yes, the passive radiator provides lower bass response. Now, the midrange stereo driver produces lower frequency ranges that do excite the passive radiator. However, since I had heard the very low frequencies do sound "better", this is where my question comes in. The two bottom 6.5'' drivers are technically for lower bass notes only (under what the stereo driver produces). These also excite the passive radiator.

Given the above, since there are no capacitors or resistors being replaced inline with the bottom two bass drivers, how is the "extreme" low frequency helped at all.

Or are you saying the crossover for the stereo 6.5'' driver does go much lower then I would expect therefore the 27uF capacitor is affecting "low" bass (sub 100hz).

I realize this is making a big deal out of nothing, but it is the engineer in me needing to understand what is going on here.



Walker

dorokusai

I've been here since 2003, heard the changes in the LF and grudgingly recommend xover upgrades when neccesary or needed.

The very low end of the SDA1 is a product of the mid-bass drivers in the loudspeaker, coupled with the passive radiator.

EDIT: Posted late....reading the earlier responses now.

Walker - When you do your upgrade, you may understand it all better. There ARE capacitors involved in the frequency path of all the mid-bass/bass/LF drivers of that loudspeaker. It's not making a big deal out of nothing, as it's a good question.

Joe08867

Actually, dudeman you are correct about the two lower mid drivers just having an inductor but the other two mid drivers are changed through the crossover. That must be what changes the sound of the low end.

I am not sure how it all works all I know is? It does work.

dorokusai

But they're all connected thru the xover network, even if they're parallel or in series(?)....depending on how you look at it. They're not connected by just an inductor....although now I finally see what you mean in regards to that schematic. I was just looking at the lower dimensional array and stereo array bass drivers, not the "bass" drivers. Look at the path of them again. A 55uf and 7.5ohm is part of the path of the positive /negative side of those drivers.

EDIT: OK....main problem. Doro looking at the wrong crossover. Correct on the SDA1A....I'm staring at the earlier version one....sorry guys. Let me investigate this closer with Polk as there's a discrepency between the schematics for that model.

Joe08867

I looked at the wrong one the first time too.

leftwinger57

Hello again, This post is way out of my knowledge of these vintage speakers.The biggest problem that I have and I might be wrong here is that there is a jumper between both left and right speakers and then a lead to the amp.
If this is true I can't see many houses or wives putting up w/ a wire that goes across what ever your logistical layout may be. For me I took both my cables and ran them the same way and nothing is seen. If a hall seperates the room and there is no crawl space how would one hide this jumper if in fact I'm right and there is a bonding cable. Also a verylaborintensive way of hiding the wires would to pull the mouldindinds and use a quick dry putty to cover the finihing nail holes.
Again if your in a ranch style house there are many other ways of concealing said wires.

F1nut

Since you don't own any SDA's, why concern yourself with if's!?!

FTGV

Dudeman258 wrote: »

I see. I assumed the full range technically was delivered to each branch, and each passive component then limited what could go through it. If this is true, then where am I missing that there is a direct path to the LF drivers with only the inductor in between.

Please consider post #21 on this SDA recap thread (link below). If you can describe what it is I am not taking into consideration I would feel much better.

http://www.polkaudio.com/forums/showthread.php?t=65993

Walker

From the schem. of the SDA 1A it appears all 3 MW6501's in the stereo array are operating in parallel in the bass range but two are rolled off in the upper bass/lower midrange by a large series coil while the other also covers the midrange operating up to the crossover point with the tweeter.It has a standard second order low pass filter with a series coil /shunt cap.

dorokusai

There are also circuit paths on that board to parallel them in with the other mid-bass drivers, so they are in fact going thru the capacitors and resistors as stated previously.

FTGV

Where ?maybe we are looking at different models.?In the schem I looked at those three drivers do not see any additional passive components than the three I mentioned.

dorokusai

FTGV wrote: »

Where ?maybe we are looking at different models.?In the schem I looked at those three drivers do not see any additional passive components than the three I mentioned.

I'm just going by some boards for a different model, SDA2 that I have laying around. They're not exactly by the schematic either but when you look at the board, they are connected. It may certainly be different, just checking out what I have handy and what was available to me.

We'll get this sorted out between everyone involved here I'm sure.

FTGV

dorokusai wrote: »

We'll get this sorted out between everyone involved here I'm sure.

Since his inquiry was specifically in regards to the 1A the answer is already clearly provided in the schematic thus my comments are only specific to it.

dorokusai

Yeah I get it FTGV, thanks for additional clarification of your post.

FTGV

Even a casual look at the various SDA schems would show considerable differences in crossover implimentation from model to model and suceeding generations.

dorokusai

You're absolutely right. Even within that same model, they're all different.

FTGV

dorokusai wrote: »

I'm just going by some boards for a different model, SDA2 that I have laying around.

2,2A or 2B?

dorokusai

The final answer is that the xover schematic referred by Dudeman above is incorrect. It's even inside the SDA Compendium but so is the correct one. It has been removed from the list.

There IS a 55uf Capacitor and 7.5ohm Resistor inline with those woofers via 2nd order setup. No Polk loudspeakers work with only an inductor, period. NO first orders.

Dudeman258

dorokusai wrote: »

The final answer is that the xover schematic referred by Dudeman above is incorrect. It's even inside the SDA Compendium but so is the correct one. It has been removed from the list.

There IS a 55uf Capacitor and 7.5ohm Resistor inline with those woofers via 2nd order setup. No Polk loudspeakers work with only an inductor, period. NO first orders.

Wow, thank you for your help! So where can I go to see a correct schematic, and how did that incorrect schematic even come to be? It looks to be a genuine Polk part drawing.

At any rate, I can sleep at night knowing the truth

Thanks for the patience everyone. At least something constructive came of this.

Walker

dorokusai

The correct one is still posted. Darque Knight was researching his SDA Compendium when he compiled the schematics for the SDA series and was being thorough. When I was able to get access to all the historical schematics, I PDF'd everything I could possibly get hold of.

It's simply a first draft schematic and it's obviously genuine. The accurate version is the first one(from the section) that has the handwritten component values on it, which is what I was going by originally when we started this conversation. Hence, the reason we weren't understanding one another.

I knew I wasn't crazy when suggesting the values but also didn't think about that other copy being different at the time since I never looked at what you had posted until later. I have the direct copy originals, the SDA Compendium and other Polk stuff that I can't post for reference.

Whatever, problem solved. Thanks for the question Dudeman as it helped me clear an issue up internally and remove a confusing document from our help area. Good luck with your project.