If you go down enough octaves, tempo is tied to the drone note. Different chords have different rhythms. What you hear are not pure notes because I have the distortion and some harmonics turned up so that it's audible. But this is part of the point I would like to make about thinking in terms of notes as being simplistic. When you play fretless, there are no special notes anywhere. There are only special ratios of one pitch relative to another. They make interesting rhythmic patterns that you can hear below the audible tones:
Imagine your BPM being midi note -24 or whatever it maps to... something absurdly low. Then the drone note is some octave up. double time is an octave. triplets are a fifth in some octave, etc.... it could be interesting to connect the two by having a sound with some absurdly low octaves in it.