I saw these definitions somewhere or other --- a virtue is that, being based on octaves, they're easy to remember:

10-20 infra bass

20-40 low bass
40-80 mid bass
80-160 high bass

Greg
VP180, M80s, M22s, QS8(4), CSW S305s, EP500, Pioneer VSX-90
M2i, M3(2), Pio vsx-1020