If you do the math it turns out that a damping factor of ~8 causes a
frequency response deviation of 1dB max (if speaker impedance varied
from the nominal value to infinity), which is barely audible. That's
absolutely worst case. So any damping factor of 16 at all frequencies
and levels is almost certainly inaudible. Dick Pierce's article shows
that with a reasonable dynamic speaker a DF of 5 is quite adequate.

TB