String tone of any basic frequency is always a function of the fundamental and it's harmonics which vary from instrument to instrument. Otherwise a given frequency, bass or not would sound the same from every string instrument. To speake about string tone without the harmonics, or indeed any instrument without its harmonics makes no sense.
Bass- at what frequency does it change from sounding like a string to just a low tone?
I have two subs and speakers I like. I have little experience comparing them to anything else. As the frequency of a given note goes lower, at some point in my system it stops sounding like an instrument making the sound and instead it just sounds like the sound. I’m not crazy about this, but maybe that’s how it is for everyone?