Apparently Arturo Melocchi became familiar with this technique - referred to as the lowered-larynx technique - around 1930. He learnt it from a Russian voice teacher who had learnt it in China, but I am unfamiliar with any further origin or tradition. Melocchi taught in turn the technique to Del Monaco, who, from what I have heard, initially had a rather thin voice and had difficulties with being heard in the opera (I believe this claim comes from Del Monaco himself). Del Monaco changed his initial voice teacher, Raffaelli (after Luisa Melia-Palazzini), for Melocchi in 1935 and obtained eventually a strengthened vocal delivery, brassier sound, more baritonal, with more heft. It consisted in lowering the larynx, keeping the jaws open as if yawning, but it was considerably difficult to sing this way and the trade-off was loss of modulation and dynamics, and Del Monaco sang in a declamatory manner most of the time. This was perhaps his best and worst quality at the same time. Much heft where needed but also a lack of subtlety and softness where needed. Yet Del Monaco was somewhat fascinating in roles which probably were not considered suitable for his voice. Other tenors were not equally successful in applying the technique and sang fortissimo without modulation whatsoever, which was pretty tiring, hence the comments that Melocchi's technique suited Del Monaco and no one else.

However, Corelli also used the technique, he went to Melocchi a couple of times, but mainly picked it up from a another Melocchi-student and friend, Carlo Scaravelli, besides putting Del Monaco's singing to scrutiny, and adopted a less extreme variant of the technique. Corelli didn't keep his larynx low at all times, as did mostly Del Monaco - and furthermore, as low as it would go - but instead modulated the position of the larynx, making it "float," as he said. In that way he managed to colour more than did Del Monaco. And cartainly, Corelli was known for his excellent diminuendi...

Corelli claimed in an interview with Stefan Zucker for New York's WKCR-FM that he lost his voice after studies with soprano Rita Pavoni, i.e. he lost his high notes and continued his studies as a baritone. The technique he used led him to close his throat as he overused the throat muscles preventing the voice from passing through freely and he claims that the technique taught by Melocchi helped regaining his freedom in singing and his high notes.

Mario del Monaco's brother, Marcello Del Monaco, also studied with Melocchi and later on taught a number of Italian tenors who became dominant in Italy during the 60's, counting Nicola Martinucci and Giuseppe Giacomini, as well as other less known tenors such as Limarilli, Cecchele, Merighi and Rumenean tenor Murgu. Apparently a similar technique was taught in the US by vocal teacher Douglas Stanley during the 20's and 30's.

Apart from a muscular, thick and non-modulated sound, and at times difficulties with legato, the Melocchi technique also strains the vocal chords immensely, and Melocchi was often referred to as a "throat-wrecker." It seems Del Monaco was rather worried that this might shorten his career, but it seems the advise he got was that it was better to shine brighter if shorter, than longer and less bright...

Still, teachers who advocate the technique, make a distinction between pushing the larynx down with the throat muscles and holding it low or down by expanding with the muscles against the ribcage. The first causes strain and damage, the latter does not. The question is providing the right resonance cavity for strong voice production, for which the muscles around the throat must be strong, providing a solid wall and the more the throat is approximating the tube of a horn, the more powerful the sound will be.