I have question about a nearly-unheard of oktavism technique. It is similar in nature to subharmonics. Apparently there is a technique where you "swallow your larynx" and depress is a very large amount using muscles almost never used for singing. Then, once it is extremely depressed, you can sing notes 2-3 steps lower than your usual low. I've been told by multiple people the oktavist of the Kovcheg ensemble, Pavel Myakotin uses it for notes between B1 and D2.
I've also been told some operatic singers, in addition to some Bassos, use it.
Does anyone know anything about this? I'm interested in it very much.