By simultaneously combining the sounds of two didgeridoos, a desired state of consciousness can be induced in the listener. For example, when one didgeridoo is played in the key of Bb (fundamental frequency of 58 Hz) and a second didgeridoo is played in the key of C (65 Hz), the difference between the frequencies is manifested as a subtle pulsing (in this case 7 Hz). The listener’s dominant brainwave state will sync with this pulsation in a frequency-following response known as brainwave entrainment.
Entrainment is a phenomenon seen is a wide variety of different natural circumstance. In the field of chronobiology, the study of biological rhythms in living organisms, entrainment is the synchronization of a circadian rhythm with the rhythm of an external pattern, such as the synchronizing of women’s menstrual cycles with the phases of the moon or with one another in a group.
If brainwave entrainment leaves you with unwanted side-effects (see below) or discomfort, you’re probably encouraging a range of brainwaves that are already excessive in some area of your brain. The way around this is to get a brain map to see what your brain’s strengths and weaknesses are, and see what (if any) brainwaves could use some encouragement.