This is the term I use to describe what I do with my voice. Sometimes I incorporate words and c﻿hants, so it could be called "mantra chanting", but often I simply utter monosyllabic﻿ sounds of different keys/tones to create different vibratory sensations. I usually feel inspired on the spot to weave these sounds into a simple song-like structure to accompany the atmosphere of the given space and the vibes of the participants in the class. Occasionally I sing while playing some recorded music, and if this is the case I harmonize with the background music so that the experience and effect of the sound-relaxation can become amplified.
In a typical group session I employ this technique during the shavasana when the participants lie down on the floor to relax for 5-10 minutes at the end of the class. In private classes the clients have often requested me to do this for 40+ minutes to make it a session in its own right.