SDA - SRS Questions ( moved to here )

Loco57

:oThankyou for allowing me to join your forum, I have a couple of questions that I hope some one here may be able to help me with. I have a pair of SDA SRS speakers that I bought new from the dealer in Melbourne Australia and I am in the middle of modifying them for a better sound.

I have the following Quoestions:
How do I determine the series of these speakers? Drivers are marked with March 1986 and the tweeters are the dead fish eye type.

On stripping the cabinets I found that in a lot of cases the glued joints were only on one side and the amount of tipped in glue just run everywhere was incredible.

On one of the speakers I have rewired the internal wiring with 12 gauge OFC good quality wire and soldered all the board and speaker connections, my question on this is that why is the polarity crossed on both the vertical Bass/Mid speakers between two and three on both sides?

Doesn't this present a potential short of the polarity when wiring back to the crossover? I have a great deal of problems getting my head around that one if it is right. To my knowledge the cabinets have never been apart is it possible that they were wrongly wired at the factory?

If someone could let me know what series this speaker is and what wiring configuration is correct and if possible a wiring diagram I would be eternally greatfull.

Currently I am running these speakers in bi Amp mode with a Stax CAY pre amp and a pair of RB1090 power amps, the modifications to the first cabinet are as follows.

All angle joint surfaces internally have been braced with 25mm Hardwood quad after all the original excess glue was removed ( literally someone just tipped a whole pot in and let it run ) then approximately 10kg of spray in body deadner coating all internal surfaces.

Fabricated an 18mm mdf duct under the tweeters between the cutouts sealed at the top of the cabinet and open just above the crossover to allow cables to be run. put an additional 18mm mdf panel behind the ABR to give it a bit more meat.

Replaced the speaker terminal block with a 2.5mm thick stainless steel plate fitted with three sets of gold lock h/d binding posts for both bi amping and SDR Cable.

Cut and rolled two sets of five thick 25mm Dacron filling fitted under the Bass/Mid drivers full length of the cabinet, silicone sealed the top timber section of the cabinet so no vibration.

As I have only modified one cabinet so far I wanted to gauge the difference between the two a little hard to gauge just yet as the amps are brand new and sounded very harsh at first but as the night wore on it all started to mellow.

The modified speaker has less volume at the same setting but showed a distinctly tighter more defined sound and the tweeters sounded more defined and less shrill at volume.

As for image it appeared to be slightly to the right but I am not convinced that all is right in that area as it still doesn't sound quite right so I need some help.

Thankyou in advance and I look forward to being a part of this forum.

Boywonder

Be careful stuffing the enclosure as you will probably change the tuning of the passive radiator, as adding a little fill can increase the "effective" enclosure volume but too much (as well as 20 lbs of sound damping goop and additional bracing) will decrease enclosure volume.

You are sort of flying blind without checking the system resonance (fc I think) of the unmodified system and comparing it to the modified cabinet. Also, the stuffing changes/cabinet stiffening should not have any impact on the tweeters, as they do not rely on the compliance of the air in the enclosure for proper operation, only baffle geometry and crossover slope, etc. You can measure system resonance with a SPL meter, function generator (to make sine waves), an ohmmeter, and an amplifier.

I would guess that the polarity issue on the mids has to do with the fact that they are the dimensional drivers getting the difference siganl from the opposite channel. One of the experts here can probably explain the wiring in detail.

here is link to the schematic:

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

nms

Be careful in there - you're adding a lot of stuff without knowing how it'll affect the sound!

Oh, and if they worked before, obviously the wiring was right (I can't grasp how it works either from staring at the schematics).

hearingimpared

Welcome to Club Polk.

Loco57

Thanks for the Pdf link hopefully I will find what I am after, I understand what you say about the dampening effect of the Dacron and body deadener with the bracing as my aim was to make the cabinets more ridgid and less resonance. With the sound from the modified cabinet being noticibly tighter and no after ringing as per the stock cabinet I believe this an improvement.

Removing some of the Dacron is no big issue just a matter of tuning as I could have possibly gone overboard a little, tweeter enclosure was just an experiment probably less resonance from the main drivers as a result, smoother sound.

The Quad bracing has noticibly reinforced the cabinet even prior to the body deadener being sprayed in just tapping the cabinet showed this, now if I can just get this wiring issue sorted then I can fine tune then do the other cabinet.

LAS, what can I say the wife just doesn't pay me the same amount of attention anymore so I have to do somehting with my time or I would go Loco!

Loco57

NMS,
its funny but looking back I always thought soething was just not quite right with the speakers but could never put my finger on it, the sound was harsh at times and the image different! I put this down to the SDA effect?

Originally I drove these speakers with a pair of Lux M300 amps but unfrotunately a recent lightning strike took these out and they are at the repairers to see if they can be saved hence the RB1090 amps at the moment ( I actually bought 4 of these for an 8.2 system I am building up ).

H/I If you really are hearing Impaired its a waste of a nice 2 channel rig!

McLoki

harsh sound I would say comes from the SL2000 tweeters. (kind of white - fish eye - looking) Big upgrade by replacing them with the new RDO tweeters. If you do have the SL2000, you have the original SDA SRS speakers.

The different image is part of the SDA effect. (you do have the interconnect cable connecting the two speakers together don't you?)

Michael

heiney9

It would be nice if all the posts associated with this thread got moved too! I said something but I forgot what I said or rather how I worded it. I hope that "lost" post doesn't get subtracted from my post count :D:).

Because the dimensional drivers in SDA's run out of phase that may be why you notice the wiring of some of the drivers like it is. Follow the schematic closely and/or use the unmolested x-over of the other speaker as a guide. SDA's aren't wired like a conventional speaker.

H9

heiney9

SDA's are a unique bird and don't respond well to drastic changes so be careful with all your messing around. I'll reiterate Follow the wiring schematic very closely. If you screw with the internal wiring by trying to change it you will lose the SDA portion of the speaker and who knows what possible damage could come to the drivers, x-over and/or amplifier.

The umbilical cord that runs between the speakers connects the dimensional drivers and if those are wired incorrectly you may end up with a dead short or some other unwanted electrical situation. If you don't understand how they work it's best to leave them alone until you do.

Welcome to CP and don't take my post the wrong way.

H9

heiney9

Also be aware that some SDA's (yours) can not be run with non-common ground amplifiers. The Rotels you are running in bi-amp mode are common ground. You wouldn't be able to bridge an amp and run the SDA's or use stand alone mono blocs or other non-common ground designs.

H9

Loco57

Bang on McLoki fish eyes is what I have! And yes the interconnect lead is attached although not a lot of difference to tell the truth.

H9 its called a Seniors Moment after a while you just don't notice.......all this moving posts what are you a fencing contractor?

Just for the record I am neither a Crossover or A molester, all items in the original cabinet are as they were delivered this is how I know the wiring on the molested oops altered cabinet is correct to the original layout I think!

The common ground issue with amps on these speakers I am well aware of and its implications for both electronics and speakers so no fear in that department, I will study the downloaded Pdf and try and work it out from their.

Thanks for the information gentlemen.

Loco57

By the way what are the New RDO tweeters? Are they a direct replacement? No cabinet mods? ect.

heiney9

Loco57 wrote: »

By the way what are the New RDO tweeters? Are they a direct replacement? No cabinet mods? ect.

Direct drop-in replacements using a Silk Dome. They were R & D'd by Polk and are a smoother more refined tweeter than the sl2000. The sl2000 has a documented +5dB peak at around 13.5kHz which can be fatiguing and to my ears has a nasty resonance on certain female vocals and a "ringing, unnatural" tone on piano. The RD0194-1 takes all this away and most feel it's a night and day improvement over the sl2000.

While your in there many of us have refreshed the x-overs with higher quality non-electrolytic caps and Mills wire wound resistors. I have a pair of 1C's with Sonic Caps, Mills and RD0 tweeters and they are superb. I also refreshed a pair of Monitor 5B's with Solen caps, Mills resistors and RD0's and they were transformed into a very nice pair of speakers for my office rig.

These types of upgrades, while pricey, will really give you a vast improvement in sound. Bass will tighten up considerably, the sound stage will open up considerably and everything will be smooth and effortless. Very open, slightly laid back, detailed, etc. I wasn't completely convinced until I made the changes and it was well worth the investment. Only regret I had is why I didn't do it sooner.

Purchasing the RD0's and x-over parts is an expensive endevour and fitting the new 60% larger parts on the board is a PITA, but it can be done if you know your way around PCB and can use a soldering iron.

There are many many posts with pics, instructions and hints to do this. Pull up a chair search the archives and have some fun.

H9

Loco57

Thanks once again H9 I will do a search and see what I can find on the subject, I assume the RDO tweeters are avaialble from Polk?

McLoki

BTW - direct replacement. No mods needed to the cabinet.

Michael

Loco57

Well you guys sure a friendly bunch full of all sorts of top information, just to update you had an extended listening session last night and found a couple of interesting things. It appears one of my new RB1090 decided not to play the game running exttremely hot and very noisy through the speakers Harsh sound ect.

On closer inspection it revealed that all was not well from the factory ( so much for QC ) this am has only done 3 hours work if that, a loose binding post and abviously not to well internally so as a result I swapped it out for the third amp still in the box.

And well well it appears most of my alleged problems have vanished, seems I didn't stuff up the rewire after all. Both amps now running nice and cool with a noticable improvement in the sound quality as the nigh went on, definately a more defined image and tighter bass/midrange on the modified cabinet even the volume is now equal between them.

As a result I do believe I will modify the second cabinet to a simular spec with a bit less Dacron filling and then progress to the change to the RDO194-1 tweeters and the electronics upgrade as it should be very interesting to see the final outcome taking into account the experience of others who have gone this way.

While I am not a complete idiot I am no electronics wiz either if I can persuade one of you fine gentlemen to walk me through the required steps and exactly what items I need to buy and replace I would be only to happy to photograph what I have done and post it for others to have a look at and possibly follow the same route.

Structurally the modified cabinet is now light years ahead of the original build not that I am saying the original is flawed it is possible that Matthew designed a certain resonance into the cabinet for his purpose? It may be a feature of the model but more likely a commercial consideration at the time as unless you are buying a Mega dollar speaker only an true sound nut would take the time to go to this extent for an unknown gain.

I will place an order with Polk for the tweeters and take some photos of what I have done to date as the stainless steel binding post plates look quite trick, now if I can just figure out how to post pics!

P.S. I assume I can just go to Polk online and place an order for the tweeters?

nms

P.S. I assume I can just go to Polk online and place an order for the tweeters?

Call them, the number is on the support pages.

As for walking you through, if you search for "SDA SRS upgrade" (and check the "only search post titles" box, you'll get a lot of threads outlining how to upgrade the crossovers. Granted they're not really a how-to, but if you read through a couple of them it becomes clear how to do it.

Loco57

Thanks I will ring today and order, I assume shipping to Melbourne Australia is not an issue?

nms

Loco57 wrote: »

Thanks I will ring today and order, I assume shipping to Melbourne Australia is not an issue?

Uhhh, might be. Be very sure to mention you are a Club Polk member otherwise the shipping is going to really hurt!