The mechanism, briefly.
Three things move during a session. Cortisol drops, heart-rate variability rises, and vagal tone increases. Each of these is measurable. Each is associated, in the peer-reviewed literature, with better sleep, lower inflammation, more accurate emotional regulation, and recovery from cognitive load. None of this is mystical. It is the body responding to a precisely held environment.
The acoustic instruments (Himalayan bowls, gongs, crystal bowls, chimes) are tools. The skill is in how they are played and, more importantly, in how the room is held.