there are multiple "perspectives" within an acoustical space of which to view from.
take Non-Environment control rooms for example. a NE response (in the time-domain/ETC measured at the listening position) will show the direct signal and then drop off to the ambient noise floor. the speaker-to-room response is effectively anechoic - no indirect energy from the speakers (via the room / reflections) is allowed to impede the listening position. the direct signal is all that is heard/processed/measured at the listening position (for "accuracy").
now, some people will assume this "effectively anechoic" response as measured at the listening position must mean that the room itself is dead/anechoic - which can be quite uncomfortable to be in! but this isn't true at all as the front wall and floor are reflective.
so, the speaker "sees" an anechoic room (speaker-room response), but the human/listener does not. when the human speaks, moves about, etc ... there are indirect room reflections. the difference is that in this case the human is the "source" and "receiver" - and this "response" is NOT anechoic as energy reflects from the floor and front wall. but when the speaker is the "source" and the listening position (mic) is the "receiver", then the response is anechoic.
so you can indeed construct the room such that the speaker-to-listener response is anechoic and accurate ... while the room itself does not "sound dead" to the listener. it's all about perspective
it's not just the time-arrival but the gain of the energy. you'll find Binary Amplitude Diffusers (RPG BAD, for example) common in many home theaters. simply using absorption to attenuate the high-gain, sparse, early arriving signals can quickly lead to a dead room (from the human's perspective) - especially when confronted with many rows/seating positions (thus, many "reflection points"). using BAD can provide mid-LF absorption while also offering HF spatial dispersion. spreading the energy out in many directions (diffusing) by nature lowers the gain of the energy that reflects specularly to the listening position. thus, you can have some energy/reflection but it is low enough in gain as to not be destructive. it also provides a sense of "reflected energy" to the humans as they talk and move about the room and restrict the "deadness".
Very interesting (and the rest of the post which I have deleted for the sake of quoting bandwidth) and I thank you for taking the time to type it.
I think what I have managed to achieve then, probably by luck as much as anything, is the sort of thing you describe above, to some extent at least. The room is well-damped but it is not by any means totally 'dead', although some may feel that it is I guess if they are only used to highly reflective, typical living rooms. I have the feeling I am listening to the speakers and not to the room, which is what I want to achieve.
My HT room is very small - more like a control room sort of space than a living room really, so I suspect this helps me to achieve the result I am after. I sit in the near field by anyone's definition of that I think (about 8 feet from the main speakers) and so the opportunity to hear reflected or 'non-speaker' sound is limited, especially as the room is heavily treated. I realise that it may be preference but this is the result I wanted to achieve - to hear the speakers and not the room. I have, in the course of my work, spent many hours in control rooms during radio and cinema commercial sound edits, and the sound I hear in those rooms is the sound I like to hear at home. I agree this not may be everyone's taste.
My HT room is, of course, a dedicated room, so I don't actually have to 'live' in it at all - if I am in there at all I am watching a movie. This helps because, aside from the aesthetic considerations of lots of acoustic panels, the room does perhaps sound too 'inert' to double as a space where one would want to be in conversation with people (much like those sound editing suites I mention). All in all, I have never been happier with the SQ I am getting these days. My speakers are M&K S150s across the front and M&K SS150 Tripoles for surrounds and possibly these speakers suit the environment of my room well.