Polk SDA-CRS problem

Hartsfield

I recently acquired a pair of SDA-CRS speakers and stands. They came with a 20' interconnect cable. All of the drivers appear to be operating, but the balance is way off, with vocals being markedly to the right. Testing with pink noise and an SPL meter revealed that output is identical in both speakers. Shifting the balance by 5 db to the left improves balance, but the vocals are far from being distinctly centered. They sound large, as if filling the wall behind them.

What could be causing this? Crossover component failure?

westmassguy

Hi, and welcome to CP. First, we need to find out which model CRS you have.
Are they:
Dual Tweeter, with Blade/Blade Interconnect?
Single Tweeter with Blade/Blade Interconnect?
Single Tweeter with Pin/Blade Interconnect?

Hartsfield

They are Dual tweeter, with Blade/Blade Interconnect.

I downloaded "Quick Tests to Determine Functioning of SDA Loudspeakers," and here is what I've discovered. All of the drivers are functioning in a monaural pink noise test. The document suggests this shouldn't happen. Does that help you identify the problem?

If it's of any help, I'm using a calibrated Bryston 4B-ST amp, and verified channel balance with a pair of 4412's.

westmassguy

Those are 2nd Generation CRSs.
Disconnect the Interconnect Cable, and play some regular music. The Stereo Image should be dead center. With the cable disconnected only the Inner Woofers and Tweeters should be working. If the Image is not centered, check that each tweeter is working. Use a paper towel tube or similar and place it over the Tweeter dome. If one is weak or not functioning, it could be the Tweeter itself, or the Polyswitch.

Hartsfield

I unplugged the interconnect and tested channel balance with pink noise and an SPL meter. Once again the channels are within 0.5 db of each other. I then moved the right speaker to be exactly 36" (originally it was only 18") from the side wall, and things improved.

I now believe the problem is being caused by reflections from the side wall. The SDA's are different from standard monitors in that they are not to be toed-in. Being too close to one side wall and further from the opposing wall appears to cause an imbalance in perceived amplitude. Since most monitors are toed-in the impact of reflections are not as noticeable.

Is it necessary to have them equally spaced between side walls for the crosstalk cancellation to work as designed?

Also, I noticed that some CRS speakers only have one tweeter. What is the difference? I apologize for asking so many questions, but I'm new to Polk and this type of speaker.

boston1450

Yes. Any SDA speaker placement is very important. No toe. Ive never heard the 2 tweet CRS but i enjoy my CRS+ single tweet alot

boston1450

You may find this helpful. Look thru the SDA Handbook for your model & you may find helpful info http://vr3mods.com/uploads/SDA_Handbook_2011_Rev2.pdf

motorstereo

A quick and easy thing to do is use a D cell battery to make sure there isn't one driver wired out phase. That would lower output on one side and shift your imaging.

westmassguy

That's a real quick way to fry a tweeter. I spoke with him this morning, went over a few thing. It was the proximity to the side wall that was causing the imbalance.

motorstereo

westmassguy wrote: »

That's a real quick way to fry a tweeter. I spoke with him this morning, went over a few thing. It was the proximity to the side wall that was causing the imbalance.

Glad to hear the problem has been solved. FWIW I've checked many speakers over the years using a 1.5volt d cell (including my own 1.2tl's) and never fried any tweeters. Just a quick touch will let you know if the drivers are in phase and won't harm a thing.