The lowest note on a five- or six-string bass guitar is about 31 Hz (low B, B0). Some players like a low D0 and so drop a hair lower. A four-string bass, or regular guitar, goes to about 41 Hz (low E, E1). If it is close-mic'd there will be percussive content well below that from fingers striking the strings. It is that sort of percussive stuff, from kettle drums to pianos and guitars, that I tend to miss in systems without a sub or sufficient low-end extension.
IME subs, and just speakers in general, distort "ambience" and decay by ringing after a pulse. The ringing can be electrical, mechanical, or both (in reality it is an electromechanical device so you cannot really separate them). The ring frequency may not be related to the tone that started it. That is one of the reasons I have for decades preferred servo subs, or well-designed regular subs, with big amplifiers (low output impedance) tightly coupled to the driver.
"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley