Some do it better than others. ;-) Planars have been mentioned, Joseph Audio. ProAcs are well-known for "disappearing" and throwing a big, open, coherent sound stage. That's one of many things I like about my old Response 2's. I'm rarely, if ever, concious of them. Nesteroviches disappear amazingly well for an old-fashioned "box" speaker, but they're getting hard to come by and the drivers aren't replaceable.
Speakers that disappear
I once listened to some speakers where i was surprised by their disappearing act - I don't remember the brand - I think they were stand mounted. I am currently looking for speakers - not too big - and was hoping for recommendations - I know other components matter too but I understand some speakers are noted for this trait and some don't. I listen mostly to classical and vocals, lighter pop - no hard rock (I assume the Beatles and 60's count as "light" :) ) Speakers I have
Harbeth PS3ER XD,
Martin Logan Stylos Speakers (wall mounted)
Aurum Cantus Leisure 2 Speakers,
Enigma Speakers - Enigma Oremus
Had Focal Aria 906
Thanks!