So here's a question that should have an actual answer: at what hz point does the average human ear start to discern music, timbre, nuance?
Interesting question. In my opinion a single note is not music. To me music is a series of notes and rhythms structured together usually in some type of pattern. This can happen anywhere in the audible spectrum, so music would be all frequencies. Nuance probably is more open to interpretation. I feel nuance is more of a function of dynamics and is mostly affected by room acoustics including ambient noise, so in this case it also would fall anywhere in the audible spectrum. Timbre is one of the things that allows us to differentiate between instruments and I believe it is due to emphasis or de-emphasis of certain frequencies in the harmonic structure created by the vibration of the material that the instrument is made of so technically these also would cover the entire audible spectrum. Now having said that, I believe that it is the higher frequencies that give us most of the cues that we use to help us specify what we hear. At what frequency does that start? I don’t know, but my guess would be at the point where we can start to localize where the sound is coming from. For discussions sake I will take that a step further and say most of the information we use to determine timbre and other aspects of sound happen between 400 Hz and 4k Hz. Frequencies below that, in my opinion, creates warmth and the sense of power and frequencies above create the sense of greater detail.
Back to your original post.
if I were "very experienced" or had calibration tools, I could achieve similar results for much less money. (I'm not and I don't, but I also don't have the big bucks to throw around.)
Experience of course comes from doing, that is the same boat for all of us, but there are guys that have posted in this thread that can help you get started and send you down the correct path. As for calibration tools, this mic https://www.minidsp.com/products/acoustic-measurement/umik-1, REW (a free download) and a computer, and you should be good to go.
Nothing to be a feared of, we are here to help.