One technique to activate both sets of vocal folds would be lowering the larynx with the lips rounded and protruded and the vocal cords relaxed, according to La Scena Musicale. This should result in a three-note chord: one fundamental tone, one fundamental tone one octave higher and one amplified overtone.
Humans have only one set of true vocal folds for voicing, in addition to a false set of vocal folds that typically do not vibrate, clarifies the Greater Baltimore Medical Center. However, nomadic herders and monks in Tibet train their vocal cords to vibrate at two different frequencies simultaneously, as La Scena Musicale describes. In Western tradition, sounds are produced using glottal fry, modal singing (chest register) and falsetto. Modal singing and falsetto are common to Western voice training, though the technique of vibrating both sets of vocal folds would combine glottal fry and modal singing, less common in the Western tradition and the basis of the techniques used by the Tibetan monks.