Do larger planar speakers produce more accurate sound?

Sure they do chungjh. That's why so many people buy and enjoy them.

Some do have that sort of nasal coloration, some do not.  I am not a fan of most of the current production compression driver systems (e.g., Klipsch, JBL), but systems made with some very special drivers from the like of Western Electric, International Projector Company, Yoshimura Laboratories, G.I.P. Laboratories, Goto, ALE, and Cogen, for example, coupled with the right horn can sound great and not sound like megaphones.  It is the bane of serious horn fans that the most popular and common horn systems, like those from Klipsch, JBL and Altec, do have that tendency if one does not work to reduce that problem and select the right components to complement these drivers.  It is also VERY unfortunate that the best of these drivers can be extremely expensive.  I have a fried seriously looking at a single $14,000 driver which he would buy on-line in a heartbeat if the seller would do something as simple as take a dc resistance measurement.  

My first Magnepan experience was with the MMGW, the small wall-mounted speaker that’s maybe 38”x10”. A friend had them driven by a triode tube amp of maybe 40-50 watts. No bass to speak of, I think about 100hz is it. But the sound! It just came out of the air. A violin was simply a violin, a piano, etc. So I ordered a pair   and found a nice little subwoofer to go with them. At some point a familiar, favorite piece of music played and it just grabbed me emotionally like never before. So that’s what they can do, large or small. That mid-range where so much of music (and life) resides is what they do best. I still have them in my living room, where my wife was thrilled they were so inconspicuous (off-white covers) and didn’t need floor space. I have 1.7s in my listening room with 200 watts and life is good. Sure, when I was auditioning them I was drawn to another setup in another room. Wow, what realism. Oh, $50k+ Wilsons. Very nice, but I kept the $1,400 Maggie 1.7s.

I disagree with some comments that full range ribbon planars need volume to shine. This is a matter of the amp providing ample current. I have the Apogee Duetta II Signatures (about to be completely updated by Music Technology). They sound excellent at very low volumes as well. The whole frequency range is full and very engaging just as it is at louder volumes. I’m using a beast BAT VK-600 solid state amp with bat pack for extra joules of energy when needed (coupled with a BAT VK-5i tube preamp). Don’t get me wrong the large panels such as the Full Range and Diva are also very special speakers, but they have added challenges where they tend to have a dark sound to them if not optimally matched with the proper amplification and cabling. Also, they are more sensitive to the listening space and require a large room to truly shine. While the Duetta Signatures go down to around 28 Hz (stock) the FR and The Diva go to the lower 20s. These large panels also need multiple amps and with that comes the added expense and additional layer of complexity trying to get amp synergy. I like the flexibility and relatively forgiving nature of the Duetta Sigs. One thing I will say is like all Apogees they are very sensitive when it comes to speaker cables. I’ve always used the Symos Jason Bloom recommended and have been extremely happy with them since ‘88.