(turn your volume down first!)
Below are two more strongly interacting bowls:
Try listening to them one at a time, and then both together.
When they are both sounding, a complex, fast-beating inetraction can be heard, resulting from similar but different frequencies in a number of their partials. The main interactive soundscape generated, that is not present in either bowl alone, is this:
Listen to this soundscape, and then listen to it again below, in the whole sound of the two bowls:
Within this soundscape, is a double brain-wave rhythm frequency pattern, contating both a beta rhythm of about 18 Hz (beats per second), and a theta rhythm of around 5 Hz: