Dan, I do not know where you have seen a lot of food for thought, all posts above were about nothing, as I said I really do not know what this thread is all about. If your interest is the relationship between measurable and auditable and extreme frequencies then it is a noble subject but I don't think it is what you are talking about. You were talking about general applications of RTA, but I generally have difficulties is to talk with audio people about RTA.
Generally a RTA’s are very accurate and the microphones are the one which create discrepancies. Getting at good-quality an instrumental calibrated microphone is mandatory. An alternative way would be to build a correction chain in mic-preamps and to calibrate against reference microphone… however a properly calibrated microphone and RTA are just very beginning of the entire RTA saga.
Audio people attribute to RTA some kind of supernatural meaning, without spending efforts toward interpreting the RTA measurements. RTA measurements themselves are completely bogus and irrelevant unless they are viewed in intelligent format. Where to measure? How to measure it? What kind signals to use? How to correlate all conditionals parameters with what RTA outputs? And of course the most important is how to or correlate the result of RTA measurements we is listening experiences of the given playback installation. I do not know how for others but it took for me approximately 5 years to measure and to listen until I begin to understand what is really important in the RTA interpretation.
Also one very-very important moment that unfortunately many audio people do not “get”. RTA shows just amplitude but does not show the reasons for that amplitude. We, as humans of course register amplitude but we also are capable to recognize and to be influenced by them means by which the amplitude was reached. That is very imperative concept because the correct understanding of amplitude is possible ONLY in context of the methods which created that amplitude. So, answering the questions that you did not ask: the linearity of frequency response is very positive and very important thing but only if the linearity was achieved by only “proper ways”. The Cat
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche