Here are some screenshots from various EEG studies that I did with subjects receiving the sound meditation in which I use harmonic overtones-producing instruments to a clearly audible level. Basically, it shows to what extent the brain activities (the peaks in different colors) in both hemispheres diminish or even flatten when certain harmonic overtones-emitting instruments are played, and the level of synchrony and coherence that resulted in both hemispheres. Notice the numbers on the bottom in both hemispheres. These are the brainwave cycles measured in Herz (Hz. cycles per second).
These are very complex scans and there’s a lot more I can say about each one.