I use two sinus tones 57,5hz and 60hz to produce a resonance/interference tone, the third tone. The tones are triggered with ca. 5 sec. interval. First we hear the 60hz. tone and then the 57,5 hz. tone. They play all to gather for 30 sec. parallel for 20 sec. it is then they produce the 2,5hz. resonance tone, see fig.1. Delta waves lies in the range of 0,5hz. and 4hz. and is a state the human brain works in a deep sleep.
Two sinus tones 60hz and 54hz are produced trough the aluminum plates who resonates and create an interference tone of 6hz-Theta wave. fig.2 Theta waves lies in the range of 4hz - 6hz and is thought to accompany mental imagery and creativity.