Hi Thor,
Just to confirm, I did get your email and I passed it on to my associate Scott to answer. He's away on vacation until Saturday, and he'll address all of your other questions as soon as he gets back.
> My room seems unnaturally even, without big dips or bumps, which seems to go against what appears on most sites selling products. <
Yes, but if your room is very large that would account for some lack of peaks and deep nulls. You didn't mention the size of your room in your email to me, or in this post, so I can't comment further without knowing that.
> the measurement (C/slow on a Radio shack analogue meter) changed by up to 5dB as I moved around in the room (even though the meter is stationary...) <
Sure, that makes sense. The response at any given cubic centimeter in a room is the combination of the direct sound from the loudspeaker(s) plus
many competing reflections. So when you move around your body is blocking at least one of the reflections compared to where you stood before. It also makes sense that this will be more pronounced at higher frequencies.
> Was my body functioning as an absorber and affecting the sound pressure around the meter? <
Probably not an absorber as much as a simple barricade.
> By simply moving my head and/or changing my height (stooping over) I could hear nodes and modes, and the dramatic change of loudness, from almost non existent to exceedingly strong. <
This too is very common. In fact, this is the main reason I put test tones on the RealTraps site - to hammer home how bad the LF response is in most rooms, and also how severely the response changes over even small distances. Here's another article, on my personal web site, that examines this even further:
http://www.ethanwiner.com/believe.htmlThe main purpose of this article is far removed from acoustics, but the research and measurements shown are relevant to your questions.
--Ethan