Polk SDA2s and dimensional tweeters

geppy1

Hi, I have had Polk SDA 1s,1Cs and 2B TLs . I recently sold the 2B TLs and for some reason a month later grabbed some beatup SDA 2s with the SL 2000s side by side I was thinking i could put the drivers in my RTA 12s. Anyway I listened to them and they sound good maybe slightly bright. but not harsh at all.. I then disconnected the outside tweere and now they sound really nice and balanced. In fact they sound alittle more full then the 2Bs did with a better midrange . Then again there are 2 stereo drivers verses 1 in the 2B

I also noticed something else. With the dimensional tweers hooked up I played the 3rd song on Jackson Brown's Running on Empty and JB is talking to a bandmate about Mozart and the band member is righ in front which is not the way any other speaker does it. He is usualy way to the right. When I disconnected the dimensional tweeters he moved out to the right like normal and yes the outside 6.5 dimensional speaker was working. I noticed the same thing on Bob Siegers last track on Against The Wind. Back up singers at the end of the song , first to the right then left then right then left. With the dimensional tweeters hoked up it did not do that.

Point is they seem to sound way better and more balanced with the outside tweeters disconnected and as a whole seem slightly more filled in in the midrange then the 2B.

Not that it really matters but did Polk ever come out and say discconnect the outside tweeters?

BKphoto

i think that is a standard thing to do...seems i've heard it before...

westmassguy

The 3nd generation SDAs did away with the side by side tweeter arrangement. It was determined that the dimensional tweeter detracted from the sound quality with some recordings, as you've discovered. I doubt Polk would recommend disconnecting the tweeter, but most do. I rebuilt a pair of 2s a few months ago, and with the new RDO tweeters, the held their own against my 2ATLs. The 2nd stereo driver is called a bass driver. It crosses over very low. It's purpose was to make up for the loss of bass caused by the dimensional woofer being out of phase. This was later corrected with the "full compliment sub-base drive circuit" starting with the 3rd generation.

Dawgfish

One of the first mods I did on my original CRSs was to disconnect the dimensional tweeters and replace the stereo tweeters with RDO-194s. It made a huge difference. I've since done the hurricane nut, armaflex, dynamat, and polyswitch mods. A little over $100 in mods and a little elbow grease has taken these things several wrungs up the ladder. I'll probably redo the crossovers one day, but they sound so good I'm not in any rush to do so.

motorstereo

You could also pad the tweeter with a 1 or 2 ohm resistor to tone it down a bit rather than completely unhooking it. I did that to the dimensional tweeters on my CRS's and it helped with the spacey sound.
There's something about completely unhooking a driver that just didn't seem like the right thing to do to me.

pitdogg2

I wonder what the effect would be to run 2 stereo tweeters out of the stereo side of the crossover?

westmassguy

pitdogg2 wrote: »

I wonder what the effect would be to run 2 stereo tweeters out of the stereo side of the crossover?

Very hot top end. The dimensional tweeter is at a reduced level, and out of phase

pitdogg2

yes i understand that but with the appropriate resisters I'd think you could tame that.

westmassguy

Yeah, but then you'd have two different point sources 12" apart. You'll loss imaging, some detail, and lobing, comb filtering may be a problem

pitdogg2

westmassguy wrote: »

Yeah, but then you'd have two different point sources 12" apart. You'll loss imaging, some detail, and lobing, comb filtering may be a problem

gotcha like old Sansui's or Kenwood speakers that had drivers all over the place with many tweeters and a super tweeter.:)

westmassguy

What I do is either paint the old SL2000 satin black, or if I have a defective pair of SL2500s, I'll put those in, for aesthetics, to match the RDO-194s

geppy1

I was in the biz back in the day and even remember at that time talk of disconnecting them What i find strange is the shift of people onstage Another thing on X over points Later units had the 6.5s coveing 50-2000. These cover 50 to 2500. Less load on the tweeter and i think that makes a difference Not a big difference but it is in the critcal midrange.//vocal area. One of the reasons I really like 10s very open midrange with the 6.5s covering 60 to 3000 and the 10 inch taking care of the low bass and the tweeter just the very top.

BKphoto

[QUOTE=geppy1;2043014 One of the reasons I really like 10s very open midrange with the 6.5s covering 60 to 3000 and the 10 inch taking care of the low bass and the tweeter just the very top.[/QUOTE]

then you would really like my frankin 10b-2A's

machone

What if two stereo tweeters were tamed with resistors and then were mounted vertically? Would this stacking eliminate two point sources? I know that there is not enough room in the enclosure but what if we thought outside of the box (literally). Do tweeters have to be mounted inside the enclosure? For a test one could be mounted in a solid block of wood and secured to the top of the enclosure. I am new to this forum so please don't ban me!

F1nut

Bad idea. What can be done and has been is to remove the SDA tweeter entirely, move the regular one to the center, then seal off the original holes. Apply new vinyl on the front and it's like the SDA tweeter was never there.

westmassguy

F1nut wrote: »

Bad idea. What can be done and has been is to remove the SDA tweeter entirely, move the regular one to the center, then seal off the original holes. Apply new vinyl on the front and it's like the SDA tweeter was never there.

That's not even necessary Jesse. I mentioned earlier in the thread that I had rebuilt a pair of 2s, and just put a dummy SL2500 in place of the Dimensional Tweeter for aesthetics. I did the exact same upgrades on the 2s as my 2As, Sonicaps, Mills etc.. Comparing them side by side with my 2As, the soundstage, detail, and crosstalk cancellation were identical to my 2As. The only difference that was noticeable on certain recordings, was the deep bass wasn't as strong as my 2As. The 2s lack the sub-bass drive circuit, and my 2As, had the Erse SuperQ Inductors. If I had the original sub-bass drive inductors, they probably would have sounded the same.

machone

Boy am I enjoying this forum! Very exciting as I have a pair of SDA-1As that I bought in Atlanta in the early 80s. They are in excellent condition and I want to upgrade them to their maximum potential. I have not ordered any parts so I am starting with a clean slate. Westmassguy: Is it possible that I could eliminate the SDA tweeter and upgrade my SDA-1As similar to your SDA-2ATL?

westmassguy

machone wrote: »

Boy am I enjoying this forum! Very exciting as I have a pair of SDA-1As that I bought in Atlanta in the early 80s. They are in excellent condition and I want to upgrade them to their maximum potential. I have not ordered any parts so I am starting with a clean slate. Westmassguy: Is it possible that I could eliminate the SDA tweeter and upgrade my SDA-1As similar to your SDA-2ATL?

I see no reason why you couldn't

F1nut

westmassguy wrote: »

F1nut wrote: »

Bad idea. What can be done and has been is to remove the SDA tweeter entirely, move the regular one to the center, then seal off the original holes. Apply new vinyl on the front and it's like the SDA tweeter was never there.

That's not even necessary Jesse. I mentioned earlier in the thread that I had rebuilt a pair of 2s, and just put a dummy SL2500 in place of the Dimensional Tweeter for aesthetics. I did the exact same upgrades on the 2s as my 2As, Sonicaps, Mills etc.. Comparing them side by side with my 2As, the soundstage, detail, and crosstalk cancellation were identical to my 2As. The only difference that was noticeable on certain recordings, was the deep bass wasn't as strong as my 2As. The 2s lack the sub-bass drive circuit, and my 2As, had the Erse SuperQ Inductors. If I had the original sub-bass drive inductors, they probably would have sounded the same.

There was someone here years ago that at first disabled the SDA tweeter, but wasn't happy with the results, he then moved the regular tweeter to the center as I noted above and reported that fixed what he wasn't happy with. It seems perfectly logical to me that an off center tweeter is less than ideal.

Mystery

F1nut wrote: »

It seems perfectly logical to me that an off center tweeter is less than ideal.

Then what do you say about mirror imaged speakers that have tweeters off center?
Same looks when only the inner tweeters are used in SDA 2's.

F1nut

Then what do you say about mirror imaged speakers that have tweeters off center?

SDA's are different animals.

westmassguy

F1nut wrote: »

westmassguy wrote: »

F1nut wrote: »

Bad idea. What can be done and has been is to remove the SDA tweeter entirely, move the regular one to the center, then seal off the original holes. Apply new vinyl on the front and it's like the SDA tweeter was never there.

That's not even necessary Jesse. I mentioned earlier in the thread that I had rebuilt a pair of 2s, and just put a dummy SL2500 in place of the Dimensional Tweeter for aesthetics. I did the exact same upgrades on the 2s as my 2As, Sonicaps, Mills etc.. Comparing them side by side with my 2As, the soundstage, detail, and crosstalk cancellation were identical to my 2As. The only difference that was noticeable on certain recordings, was the deep bass wasn't as strong as my 2As. The 2s lack the sub-bass drive circuit, and my 2As, had the Erse SuperQ Inductors. If I had the original sub-bass drive inductors, they probably would have sounded the same.

There was someone here years ago that at first disabled the SDA tweeter, but wasn't happy with the results, he then moved the regular tweeter to the center as I noted above and reported that fixed what he wasn't happy with. It seems perfectly logical to me that an off center tweeter is less than ideal.

Actually, it's not off center. It's on the centerline of the stereo drivers.
The dimensional driver is outputting a reduced, out of phase signal, which should have no affect on the stereo tweeter.

machone

Is it unusual to have a crossover that is different than the published diagram?
My SDA-1A crossover is slightly different than the one that I downloaded.
1. My system uses external fuses and I don't see any polyswitches.
2. The resistors in series with the tweeters (SL1000) are 4 ohm not 3.5 ohm.
Everything else is identical to the SDA-1A diagram. No large caps or extra circuitry.
Note:
The bass drivers are MW6600X
The stereo driver is MW6600X
The SDA driver is MW6501
This is the right hand speaker. I have not opened the left hand speaker yet.

F1nut

Actually, it's not off center. It's on the centerline of the stereo drivers.

You know what I mean. There is a reason Polk put the tweeter(s) in the center on all later models.

F1nut

Is it unusual to have a crossover that is different than the published diagram?

Not at all, Polk changed things on the fly in those days.

machone

I looked at the revision block on the diagram and sure enough it shows that the resistor was changed from 4 to 3.5 ohms, the fuses were deleted and the polyswitches were added.

westmassguy

F1nut wrote: »

Actually, it's not off center. It's on the centerline of the stereo drivers.

You know what I mean. There is a reason Polk put the tweeter(s) in the center on all later models.

Jesse, you should know me better. I wasn't being facetious, or disrespectful. Your recollection was one persons opinion from several years ago. My point was, I rebuilt a pair of 2s for a customer, soup to nuts. I did listening test when I first received them, and besides the awful SL2000 Tweeters, there was an odd phasey sound with certain recordings that I had never heard before. My CRS+s and 2As do not produce that effect. I disconnected the dimensional tweeters, and listened again. The odd effects of the dimensional tweeters were gone, but the interaural crosstalk cancellation remained. After the rebuild with new caps, tweeters etc., they sounded wonderful. They held their own for the most part, against my 2As. My 2As have 198s and a bit more detail, and go a little deeper due to the sub-bass drive circuit.
For all we know, on the single tweeter models, they moved it to the center for aesthetics. Look at the 3.1, it has an MTM arrangement for the stereo drivers, and a single dimensional woofer off to the side. Why was it done that way, instead of putting the tweeter in the center? Who knows, I'm not privy to that information.

F1nut

David, I'm not doubting your findings. It just makes sense to me that the tweeter in the middle would lead to a more coherent sound. I vaguely recall that was the reason Polk gave.

I forgot about the 3.1TL's, good point. They are a bit of an odd duck.

westmassguy

F1nut wrote: »

David, I'm not doubting your findings. It just makes sense to me that the tweeter in the middle would lead to a more coherent sound. I vaguely recall that was the reason Polk gave.

I forgot about the 3.1TL's, good point. They are a bit of an odd duck.

See that's where I find it odd that they would center it for SQ. The dimensional woofer is out of phase and rolled off below the tweeters output. It's certainly possible that some lobing occurs due to proximity of the woofer below. This would be mitigated by moving the tweeter to the center, like Monitor 10s for example, but the 10s dual woofers are receiving the same signal. I have to say the 2s I did sounded real sweet.

machone

Westmassguy: Would my SDA-1As benefit using a Erse SuperQ Inductor for the bass drivers like your 2As? From what I have read it seems people are using it with speakers with the sub bass drive circuit and looking at the diagrams I see that the 1As are wired different than the 2As.

machone

My SL-1000 tweeters are flat and then are recessed flush with the face of the enclosure. It looks like the newer tweeters used for upgrades are not flat and will stand proud of the face of the enclosure. Would this interfere with the grill?