(turn your volume down first!)
The existence of brain-waves is now well established, and still being scientifically studied. They are wave patterns of sychronised neuron firing that occur in the brain, detectable by EEG and MEG. The main ones are classified by Greek letter names as alpha, beta, gamma, delta, and theta waves. Research has been done on their relationship with meditation and "states of consciousness".
The main brain wave frequencies (Hz or cycles per second) are exampled here (click to hear - please turn volume DOWN first). Each wave-band has a demo here of the low end of the range, and of the high end.
Delta wave low:
Delta wave high:
Theta wave low:
Theta wave high:
Alpha wave low:
Alpha wave high:
Gamma wave low:
Gamma wave high:
Brain-wave rhythm frequencies fall across the same frequency range in which regular amplitude modulation patterns occur in the sound of many singing bowls. Singing bowl normal modes of vibration tend to occur in pairs with closely similar but different frequencies (see Singing Bowls - the Secrets of Sound and Striking). This feature creates the characteristic "beating", pulsing or warble of many singing bowl partials (sound ingredients).
This range of frequencies is widely encountered in the amplitude modulations of musical sounds in general. Due to equal temperament tuning, the major thirds and sixths in the central compass of the modern piano contain alpha frequencies, the perfect fifths and fourths, delta frequencies, and the major tenths down into the bass, theta frequencies. Most people may not be aware of them, but they are there.
A given singing bowl is usually limited in the way it can create these rhythms, due to the physics of the bowl, but in some kinds of bowls, such as Zen bowls, the rhythms are especially prominent.
Brain-wave chimes (featured in the CDs Brain-Wave Chimes & Brian-Wave Chimes 2) create sounds like the ingredients or partials of singing bowls, but unlike singing bowls, are able to create distinct rhythms wholly across just one brain-wave frequency band, including the low, mid, and high part of the band. The separate ingredients are also tuned to harmonic intervals. So the sound is a unique, harmonic sound, concentrated with rhythms from just one brain-wave frequency band.
The complete set of brian-wave chimes consists of delta chimes, theta chimes, alpha chimes and gamma chimes. The gamma chimes are perhaps the most unfamiliar kind of sound.
These are loud! Please turn your volume down fist.