Over the years I’ve owned Maggei IIa’s, Tympani 1D’s and Tympani 4a’s before switching to electrostats (Martin-Logan). When I last upgraded speakers I auditioned the 3.7’s and 20.7’s Same dealer but unfortunately not on the same day in the same room and with the same equipment. So take these comments with a large grain of NaCl (salt, that is).
Both are exemplary. The 3.7’s were driven by a McIntosh front end and monoblocks. The 20.7’s by Classe electronics. I thought that the 3.7’s were a bit “livelier,” but there was a definite bass roll-off starting around 40Hz, as evidenced by ear and the Studio 6 RTA app on my iPhone. They would definitely need a pair of good subs if the last octave on the bottom is important to you. From the midbass up, they were very similar to the 20.7’s in most aspects. I thought the 3.7’s were a tad more coherent (maybe due to the more compact size), although the 20’7’s threw a grander sound-stage and had that satisfying planar bass slam in spades. Nothing quite like it.
As you know, the issue with maggies is that you need to bring some serious amps to the party - moreso with the 20.7’s. I had to play the 20’7’s a good 4 db louder (again, as measured) to get the same “toe-tap” involvement compared to other designs. IMHO, maggies need to be “biased” (by playing at louder levels) into a range of linear response to get dynamic contrasts right. That, in turn, pushes a lot of energy into the room that needs to be absorbed or dealt with in some manner.
From what I can recall, this aspect of the design is less of an issue with the 3.7’s.
Lastly, your preferred music plays a role. I thought the 20.7’s excelled on orchestral recordings but were less nuanced on, say, jazz trios and solo acoustical instruments where lower level dynamics play a bigger role.
I ended up going with Martin-Logan Summit X’s in my final head-to-head comparison with the 20.7’s, partially due to my personal situation at the moment - knowing that I would be moving several times in the next 3 years or so until we were settled in retirement. The weight, size and room persnikityness of the larger maggies tipped the choice in favor of the more svelte 'stats with bass controls to help in room setup. This situation also lead me to rule out the 3.7’s as I didn’t want to deal with the complexity of subs during our transition years.
All that said, I think the 3.7’s are the most ridiculous best-buy in audio of all time. Crazy good for what they cost.