A singer with a bass voice of the lowest range is a basso this
The basso profundo thus sings down to low D or even low Cand ... One of the 
four bassos is an oktavist who sings a whole octave below the ordinary deep 
basso, ... call unusually low choral basses oktavists even when these singers ... 
As far as requirements on the oktavist voice by Russian composers,... [DOC] [TLE] Questions from a Basso Profundo : singing - Reddit [PAR] Feb 7, 2015 ...