I recently bought these speakers used for $500 and they are truely amazing. These are full-range electrostatic panel speakers (no cones). They are just under 8 feet tall and around 11" wide. They are comprised of two electrostatic panels, one panel wide with one stacked one atop the other (Acoustat also made a 2+2 and 3+3 around this vintage which were respectfully 2 panels wide, and 3 panels wide). New these speakers apparently sold for $1800 in the early to mid eighties. I should also mention that Acoustat is no longer in business.
I've been listening mainly to Stax electrostatic headphones since 1985 mainly because I haven't been able to find a speaker that I liked, that sounded as good as the Stax, and which I could afford. I happened across these at a local dealer that also sells Martin-Logans, and I finally decided to give them a listen (after listening to the Logans and really liking them). Wow, here was a speaker that was really fast, clean, and open. I mostly listen to Pop/Jazz and I love the female voice (Kate Bush, Sara McLachlan, KD Lang, Melissa Etheridge, Loreena McKennitt), acoustic guitar, harp, and percussion. In otherwords I love midrange clarity, good high frequency extension, and fast transient attacks, and these electrostatics (plus all the other electrostatics I've heard) excel at these things. When properly set up in a room (which is difficult) they portray a soundstage that was on par with the Martin-Logans. On Philip Glass's 'Akhnaten' (Act I Scene 3), there is a GlockenSpeil that is so well defined in space that you can hear each pipe in it's own spatial location as it is struck. Also Sting's 'The Soul Cages' track 6 has two acoustic guitars layered on top of each other yet each is very well defined both lateraly and front to back. Plus you can hear great detail in each guitar (especailly when I upgraded my speaker cables to Goertz MI 1).

On the down side these speakers don't have very deep bass extension (maybe 40HZ, the Martin-Logan arieus's seemed to go just a tad lower), but the bass that is there is extremely well defined with lots of texture, and definately not boomy which I hate. Also the sweet-spot is very small. Moving even a few inches side to side will cause the 3D nature of the image to collapse, although there is little effect on tonal balance (something I did hear with some of the Magneplanars; move off center and there was a noticable treble fall off). These speakers also do not play very loud, nor do they have huge macro dynamics (ie orchestral triple forte won't be much louder than double forte). But micro-dynamics is great. Also these are not easy speakers to drive, but they aren't impossible either.

For the right styles of music, these are truely exceptional speakers (especially for what they are selling for used). If you have listened to Martin-Logans, Magneplanars, Apogees, or Quads and have been bitten by the 'panel bug', but don't have the cash resources that these speakers usually demand, keep your eye out for some used Acoustats. For the price of a good bookshelf speaker, you can get a truely high-end speaker that will certainly stay with a system through many upgrades. My only problem now is that I want to upgrade everything else to really make these speakers shine :)

Associated Equipment:
Amp: Parasound HCA500 (75Watt 4ohm, 20amp high current design)
Preamp: NAD 1155
CD: Philips 920
Headphones: Stax Lambda with SRD-7 (original design)
Interconnects: Tara Prism 22
Speaker cables: Goertz MI 1 (really great synergy with these speakers)

Rating: On absolute scale against other truely high-end speakers I've heard these rate 3.5 to 4, but given their price (used) they have to be a 5.

I had a blast with these speakers!They are floor standing Electrostats, almost 8 feet tall and they are dipoles.
I have never heard cat stevens sound better.
EXTREMELY amp critical, hard load AND ineffecient too.
They work well with acoustats own TNT amp.
Stay away from weird cables!
Lavinson worked best for me.
Had good sound from a KINERGETICS 200, but it kept blowing up.
Caution, this speaker will suck the life uot of a lot of amps!
But if you can get em singin, they are a blast.
I tried all kind of subs, nest luck ids to use crossover to roll off sub only!
Keep crossover OUT of 1+1's signal path, this means electronic crossover/
Recommended, only if you know what you are doing!

Having read the other reviews of this speaker, I just wanted to add my 2 cents worth. I have lived with my 1+1s for over thirteen years, using Acoustat's own amp and preamp. They do have a sweet spot, but with large rooms (mine was 24x21x10) the soundstage doesn't collapse as easily when moving from side to side. Moved far enough out from the back and side walls, these speakers will image as well as any I've heard (Thiel, Legacy, B&W, Vandersteen), throwing an enormously deep soundstage. Too, unlike many speakers, these throw an image that goes far outside the the speaker (this is viewed negatively by some reviewers of dipole speakers, so you have to choose according to taste). If you like "soundstage", these speakers are champs.
The original Acoustat company was purchased by Hafler, and subsequently by Rockford. A friend of mine tells me that there IS a person at Rockford that can still offer service (he just had his transformers and a panel replaced)and advice.

What these speakers do lack is KICK. If you like wide dynamic swings, a cone speaker will give you better service. If you like vocals and have the front-end that can deliver it, these speakers will let you hear an abundance of detail that is at times overwhelming. Too, unless these speakers are coupled with really poor electronics, the sound is never fatiguing.

Some people have pointed out that these speakers are hard to drive. To be driven properly, perhaps. But for smaller rooms, huge amps are not necessary. I drove mine with a 35W Yamaha receiver while saving up for the killer Acoustat amp. I've heard of some that use 35W tube amps to elicit the last bit of sweetness from the speakers with great success.

Overall, lacking in dynamics and the ability provide real slam, although they can definitely play loud. Ultimately listenable, never harsh.

During my college days I had a roomate that I shared a studio apartment with. He purchased a pair of used Acoustat 1+1's. Primarily, we used a 65 watt amp. A friend let us borrow a 500watt Crown Microtechf for a while. I have never listened to a loudspeaker that could touch the quality of these speakers. Even at soft levels I could tell a difference will the mega power; the 65watt amp just seemed to wake the speakers up. During the days that I enjoyed these speakers I usually found myself disdained at listening to anything else. I heard details in recordings that I had never heard before such as a singer smacking his lips between measures. I have described these speakers to people as 'speakers that can sing'. Here I am established with a family and profession years after college now looking for a set of these wonderful delights for my ears. I see that the company is no longer in business. How sad. What to do?