I bought the Polk SDS-400's off of Ebay about 4 months ago out of couriousity. SDS in this case stands for "Stereo Dimensional Surround". These are small bookshelf sized speakers that resemble an old pair of Polks I had but I can't remember the model, someone will look at the pics and be able to tell though. I believe everything is the same but the crossover. which George Grand has stated is a Hafler DynaQuad circuit.
Thanks to Ken for mailing me a copy of the owners manual. Both outputs from the power amp connect to the right speaker and then the left is sent over via a 1/4 inch plug. All speaker inputs are the generic spring loaded type. Speaker cable is somewhat limited due to the small terminals and then it really gets tight inside the 1/4 inch plug. The best I could do with using Radio Shack plugs is lamp cord since I was worried about the positive and negative ends being so close inside.
There is a 5 position rotary switch on the back of the right speaker that lets you choose how much effect you want. 4 positions for "SDA" if you will, and 1 to bypass everything and operate like a regular bookshelf.
Power rating: 20-100 watts/channel
Freq response: 35hz-25khz
1" Tweeter, 6 1/2"Driver
Listening: The SDS-400 was designed for surround but the manual states they may also be used as mains which is how I tested them. Even though they are rated for 100 watts I used my Denon monoblocks that are rated for 250. These have an A and B output so I was able to switch back and forth between my 3.1's. The first thing I did was compare output between the 2 sets of speakers. Using my Ref 50's test generator I measured the 3.1's and 400's from approx 8 ' away on a set volume vice power output as I have no way to check that.
(bypass position) 80db
Surround 1 78db
Surround 2 76db
Surround 3 75db
Surround 4 71db
These speakers need lots of juice to get them going. When they came out I imagine it was all pro-logic where your rear speakers weren't asked to do a lot. These days they just wouldn't cut it for surrounds unless you had plenty of power IMO.
The bypass mode is well........to be bypassed. Anyone buying these as a bookshelf will be dissapointed. The sound is cluttered and of little clarity. I can remember hearing speakers in the Walmart auto stereo display that do a better job.
Surround 4 and 3 mode improves over the bypass nicely. The soundstage for 3 and 4 is very narrow sounding though. It also sounds like vocals are coming from 20' behind the instruments while taking quite a bit of power to achieve decent listening levels.
Surround 2 or 1 is where this speaker finally had me spending some time to AB compare with the 3.1's. I have a strong feeling that some individuals that don't care for the SDA sound may actually prefer the little 400's. The soundstage opened up very well, not quite as wide as the 3.1's but you could still get some of the SDA effect. Mids and highs were very acceptable although not much on the low end until they were fed healthy power. I brought my 20-39pc+ in to help out the bass and it was just what was needed. (an SVS will normally help though)! The first surround setting gives you the most out of these speakers as far as I'm concerned. It still takes a lot to drive them but the quality of sound is enough to satisfy me as long as I have a sub to fill in the bass.
I've actually been messing around with these speakers for awhile now and some days they just seem to be less fatiguing on my ears than the 3.1's. Strange, I wouldn't get rid of my 3.1's for these but I could survive if the time came for whatever reason. I would like to try a 3000 tweeter in these to see if that would make any difference but I think that would involve some cutting. Maybe one of those Winter projects.