They do indeed have a very narrow sweet spot... Nothing else comes close in my experience. I can't see this not causing colouration etc though personally... When in the sweet spot you will be hearing the full correct amount of treble from the ESL's plus the treble from the tweeter I would have thought...
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Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
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