From the GR research video, fast speakers are called tweeters. A fast sounding subwoofer returns to rest faster, it has more moving mass and is slower moving. They go on to talk about servo subs and how they correct for that, I’m also aware 1/4 wave TL subs do well in this regard but I believe a well designed ported speaker can as well. I’m not sure measurements capture this although a poorly placed subwoofer would exacerbate it. I’m not discounting what you’re saying, I’m saying I don’t understand what you’re saying.
REL guys talk about signal hitting your subs and speakers at the same time, are you saying my SVS may have a timing issue? Would that be affected by changing distance? Is the a measurement I can get with a Umik-1 and REW that would help me discover the problem?