Room interaction is much greater for panels due to the forward and rear radiation. They are also more challenged to create the higher SPL's needed in large spaces..
Your best bet would be a narrowly focused Appolito type design such as a Dunlavy SC V or similar...these will limit the room interaction somewhat at the expense of a smaller sweetspot.
However, I would add that in general a wide dispersion speaker tends to sound the most "natural". Although a speaker that also radiates to the rear can actually over excite the room (this can simulate typical reverberant concert halls, school halls, churches and typical venues where you get a lot of ambient reflected energy - so classical concert hall goers will often favor panels foor the exciting ambient sound field. Listeners who crave accuracy tend to favour near-fields or Dunlavy designs)
Hudson - actually, insanely varied surfaces and room irregularities are a good thing with audio reproduction as they tend to disperse sound waves. That being said - windows are not. You want to treat the windows with Marigo Labs window dots, which work extremely well and have a huge WAF compared to draperies heavy enough to do any good. You should be better off with the electrostats ( M-L) than the Maggies, because the 'stators have a much narrower dispersion pattern than the planars with the ribbons. Be advised that both require a fair amount of room behind the speakers to sound their best. Have FUN!
Dipoles interact with the room differently from monopoles, and have different setup requirements for good performance. Briefly, dipole bass is smoother in-room than monopole bass, but you don't want the reflected backwave energy arriving at the listening position too soon. I suggest about 5 feet between the speakers and the wall behind them.
Also, with a hybrid electrostat, the line-source-approximating panel will have different radiation characteristics than the point-source-approximating woofer. The sound pressure level will literally fall off more rapidly with distance from the woofer than from the panel (anechoically, 6 dB falloff per doubling of distance for a point source vs 3 dB per doubling of distance for a line source). In a long room like you have with hybrid electrostats at one end, the relative balance between woofer and panel will change by about 4 dB as you go from a fairly close listening position back to the far end of the room.
I used to have a room somewhat similar to yours (mine was 31 feet long by 13 feet wide by 9 feet tall), and large fullrange electrostats worked well in it. That 4 dB variation with distance is what I measured in that room with a hybrid electrostat. I think that big Maggies would be a better choice for your room than a hybrid electrostat.
In my experience, loudspeakers with fairly uniform, preferably not-too-wide radiation patterns are a good choice for problematic rooms. Some dipoles fit this description, as do some monopoles.
I aggree with all of what Jwpstayman said, with exception of the M-L's having a "much narrower dispersion pattern." I'm using Maggies(MMg's) in my bedroom system and having very little in the way of secondary reflections from the side walls(and they are close) Excellent freq. response curve, imaging and sound stage(especially for such a small room). I only treated the wall behind my listening position(a bean-bag on the bed) with Auralex to prevent standing waves. I wouldn't hesitate to go with either Magnepan or Martin-Logan in your situation, as they are both excellent system manufacturers, and given the power, will generate realistic SPLs(at least their larger systems will). If you should need further room treatment, check these out: (http://www.asc-hifi.com/picture-panel.htm) Let your wife pick the pictures(good for the relationship). Peruse the rest of the site for some really good pointers on room acoustics. Happy listening!
Thanks all for your fantastic and detailed responses.
Jwpstayman: It's more the asymmetry that is disturbing to the ear. Immediately to the left of the listener's location you have the windows, whereas to the right you have the empty space where the room doglegs into the kitchen. That leads to a really annoying image instability - as a singer goes up and down their range they will move from side to side. I'm assuming this problem is caused by the windows, though there's other things that could be a factor (the exposed ductwork on the left and not on the right; the chaise of the leather couch). I'll definitely look into the Marigo dots - hopefully they will mitigate the problem somewhat (the double cell blinds on the windows now don't do much).
Duke: That's incredible detail, thanks. It never would have occurred to me how quickly the drop-off in perceived volume would differ as you moved around the large room. I'm not sure I can afford a full-range electrostat but the larger Maggies can be found around $1000 which seems like a feasible replacement for my PSB Image T45's.
Hudsonhawk, Maggies and Martin Logans are definitely competitors. If you read a lot of online comments, you'll find that people pretty much agree on what the tonal balance of Maggies is whether they like them or not, but then you'll find a diversity of opinion on what the tonal balance of Martin Logans is. I think the reason for this can be traced back to the Martin Logans radiating as a point source at low frequencies and as a line source at midrange and high frequencies.
Used Maggie 1.6's should work well in your room, assuming you have a fairly powerful amplifier.
save your pennies. martin logan is producing a full range electrostat, the clx. yes it will exceed your budget, significantly. it will not have the disadvantages of a hybrid electrostatic speaker. it will, unfortunately, set you back around $8000.
I don't know what your budget is but a used pair of Legacy Whispers would fit the bill nicely. They have a compound dipole bass alignment provided by four 15" woofers per side. They have a dispersion of <90 degrees at all frequencies which would meet the directivity requirement that Duke mentions above. They are designed to NOT interact with the room and having owned a pair I have to agree. Even though I have a pair listed on Audiogon right now, they have been sold so I am not trying to sell mine here. If I had a large enough room to set them up in in my new house I would keep them without a doubt. They are an incredibly enjoyable speaker system. Just my 2 cents worth and I hope this helps.
Good responses so far. Line sources are not immune to side wall reflections but seem more forgiving than typical point sources. All I can add is that line arrays (Selah, Pipedreams) have a similar radiation pattern to panels and that there are also line source/hybrid monopoles (Newform Research, Wisdom, VMPS) which may suit your requirements.
A nearfield listening position will also minimize room interaction, although it takes some getting used to.
Then again, there's always headphones...
Thanks for the interesting ideas. I like the idea of the Maggie 1.6's, though my main concern is that I can only move them out 3.5 feet or so from the wall. Hopefully that would be enough.
One thing I like about the Maggies is that there are matching centers and surrounds avaiable, and my system is about 70/30 home theater / music.
Those are very interesting suggestions, Ngjockey. The Newform Research stuff looks like it would be in my price range and reminds me of the Lineaums that I used to have. The only problem with them is that they didn't fill the cavernous room, which is why they were replaced with the more robust PSB's.
I just bought some used Innersound Kayas because they are designed to not interact with the room like most speakers. They work great in my 15x13 room. They sounded great in the much larger room of the dealer i bought them from also.
Innersound is out of business but Roger Sanders the designer is back in biz. The new company is called Sanders Sound. Roger will still provide service for Innersound speakers.
Also Innersound speakers and Sanders Sound speakers are more directional than Martin Logan because the panels are flat. The compromise is a small sweet spot but much less room interaction at mid to high frequencies.
Here's an interview of Roger Sanders by AudiogoN at The Show...
Sanders Sound hits the Sweet Spot