royjohn wrote at 2015-09-11 15:02:17
This is a four year old question at this point, but, as there is little information available on basso profundo and oktavist, I will add some information.
Operatic basses such as basso cantante descend to low E, and, as Pamela said, basso profundo roles to low D. There is a low C for Baron Ochs in Rosenkavalier. Basso profundo is usually considered to have a low C, but there are certainly singers who sing lower or who are close to low C, but "no cigar." You sing the roles which fit your range, but only those in which you are comfortable with the tessitura and other demands.
The main repertoire for the oktavist is Russian choral music and church music. An oktavist descends as far as G or F below the basso profundo's C. Some oktavists feel a transition to a register below chest voice, and there is documentation of a subharmonic vibration pattern (see the article by Svec, Schutte and Miller, "A Subharmonic Vibratory Pattern in Normal Vocal Folds"). However, the goal of vocal training would be to make any register changes smooth and hard to notice.
Bass voices continue to deepen with maturity, possibly even into old age. Some will naturally have a very low voice early and some will develop it with time. The famous oktavist Vladimir Miller has said that he had a weak low Bb at eighteen years old, yet he now has the low F.
As to the power of very low notes, they do not carry over an orchestra as high notes do. Generally composers understand this and the orchestral sound is reduced where notes below G2 are sung. If you have a strong bass voice and your low notes are consistent in volume as you descend the scale and seem large and dark, that is enough. A bass's low C is never going to be quite as loud as his C two octaves above.
While very low bass voices may still reach E or F above the bass clef and sing operatic roles in the E to E (or F) range, they may be more comfortable in a tessitura that is generally lower. In training the voice, it is important to work on and claim the extremes, but not to sing notes that are a strain.
A young, very low voice might need to sing songs in keys that are lower than other voices until the higher notes are comfortably reachable. A good teacher will know how to let the voice find where it is most comfortable and guide the student to attempt only that which is right for him at his stage or development.