I love the MBL 121s.
I had been a fan of MBL for many years but they’d always been way beyond my budget, especially the big 101s. I happened on a deal for a used pair of 121s about 9 years ago and grabbed them.
I particularly loved the tonality of the 101s - I found them extremely subtle and rich in terms of reproducing instruments and voices.
As it turns out, the omni mids and tweeter of the smaller 121s really do give that same gorgeous tone as the big speakers, though reduced in size. There is a extremely natural detail, and such a wide tonal pallete to the sound, not to mention the famous MBL 3 dimensional imaging. On some recordings, especially some natural vocal recordings I have recorded in an old hall, it’s eerie how realistic the sound is. Closing my eyes it’s more effortless to think "I’m there" than any other speaker I’ve owned.
And despite the low sensitivity, I’ve actually found the 121s fairly forgiving in terms of amplifiers. They sound bold and beautiful using 140w of conrad johnson tube amps, and even sumptuous with 14W from an old Eico HF81 integrated tube amp. Though I’m sure they would strut their stuff even more, in ways, with some expensive juggernaut of a solid state amp, I’m very happy with their performance with my tube amps.
My room is 13’ x 15.’ It’s fairly well damped acoustically with a good combination of acoustic absorption, and live surfaces (walls). I tend to like listening from between 6 - 7 feet away from the speakers.
They also have pretty good "balls" insofar as they have a solid, punchy midbass presentation.
All that said, I normally use my larger Thiel speakers doing duty. I like the fuller range sound and certain aspects of the Thiel sound as well.
But I’m never going to sell my MBLs. They produce a sound that is too special and I want to be able to visit that sound whenever I want.