Beyond a doubt, the least favorite speakers I have ever owned were the KEF LS50's. I had a 180-wpc Plinius integrated amp which drove them poorly and they were bright and harsh sounding. Of all the speakers I have personally owned, they were simply awful. My Spatial Audio M4 Triode Masters cover all the bases for me. I have heard Salk speakers at many shows and I kinda think they are much underrated. Oh, overrated as well, to my ears, are Harbeth speakers and very much overpriced.
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MY LIST OF SPEAKERS FROM 1973 TO 2019:
Rectilinear III Highboys (outstanding speakers!)
AR bookshelfs
JBL L100
Electro-Voice Sentry 100's
Spica TC 40's and TC 50's
JSE Infinite Slope 3's
Goetz MS3 Towers (I had them for 20 years, made by a boutique designer)
KEF LS50 (My least-liked speakers among the bunch)
Von Schweikert V22
Usher BE-718
Totem Hawks
SVS Black Towers heard at CAS.
Klipsch Cornwalls (modded to Cornscala's)
Tyler Acoustics Lynbrook's (fine speakers, but way way too big for my room)
Dynaudio A10, A 25, A35
KEF Model 5, 6, 21 and 28?
Blumenstein Orca's
Green Mountain Audio Rio and Eos HX
GR Research LGK
ELAC Debut B6 (didn't care for them much, rockers might prefer them)
Dali Zensor 1 and 3's (both outstanding monitors)
Linkwitz Lxmini's
Spatial Audio Hologram M4 Triode Masters (By leaps and bounds, the finest speakers I have ever had in my system)
Revel M22 (Excellent monitors)
Optimus Pro LX5 (with new woofers from Dayton Audio, these are very musical)
Gallo Strada's (small speakers with a big sound, sounding much like electrostats)