Hi, very cool! this stuff is very rarely mentioned, yet change in listening distance changes all reflections, often quite considerably. When one moves closer to speakers delay of first specular reflections compared to direct sound increases. Also their spectra changes due to different angle from speaker to reflection point, and reflection angle in relation to HRTF changes as well. Also ratio of direct to overall reverberant sound (noise in room) changes. All these affect perception some. Also the system could be run with less power and heat and excursion, and so on.A few things I find problematic:
Listening distance is single most effective way to change how a system sounds everyone should experiment with it, and it should always be given as context in any speaker/system evaluation in my opinion, has huge effect on perceived sound and as such important piece of context.
Moving oneself is also simplest, fastest and cheapest way to optimize sound of a HiFi system, way simpler than moving speakers, and instantly AB testable as it's realtime adjustment to perceived sound. But, I feel it's often ignored because idea of "main listening position" doesn't exactly promote it. Practical issues don't promote it, usually sofa is where it fits, as are the speakers. Nobody mentions listening distance in any reviews because there is no brand behind it paying for it, quite contrary system sales would likely drop if people knew about this super power, moving the butt. And, perhaps listening skill or interest toward this kind of optimization isn't high enough for everyone to be able to utilize it independently without somebody else coming over and demonstrating helping to realize there is a difference. I bet many hifi enthusiast could benefit a lot optimizing listening distance, and utilizing ability to change listening distance to improve listening skill and further refine the setup.
I bet that even with suboptimal room acoustics and speaker directivity one can get pretty nice sound, just shrink size of listening triangle enough. In a typical practical livingroon scenario speakers reside both sides of a tv, quite close to wall behind. Very likely sofa is too far away because a carpet and a table must fit between. So, go and sit on the foot rest, or on the table you might have, and take a listen. Better yet, clear out anything between sofa and speakers so you can move freely and find the good listening distance. Eyes closed. Adjust toe-in and speaker spacing if needed.
Won't fix all issues, for example the SBIR, or room modes might be unfavorable which would require some other arrangement. Still, in my opinion single most important adjustment one can do is optimize the listening distance.
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