Explaining Binaural Beat Frequencies:
EEG and the brain's state
EEG (Electroencephalography) technology is used to measure brain's electrical vibrations from the surface of the scalp. The resulting EEG pattern will contain frequency elements mainly below 30Hz. The frequencies are categorized into four states as follows:
State of mind
0.5Hz - 4Hz
4Hz - 8Hz
Drowsiness (also first stage of sleep)
8Hz - 14Hz
Relaxed but alert
14Hz - 30Hz
Highly alert and focused
The dominant frequency in the EEG pattern determines what shall be called the current state of the brain. If the amplitude of the alpha range frequencies is highest, then the brain is said to be in the alpha stage. Note, that other frequencies still exist and it is impossible to give any "exact frequency your brain is operating on". However, later references to the brain states use the simplification of assuming that such a single frequency exists.
Entraining the brain to a desired state
If external stimulus is applied to the brain, it becomes possible to entrain the brain frequency from one stage to another. For example, if a person is in beta stage (highly alert) and a stimulus of 10Hz is applied to his/her brain for some time, the brain frequency is likely to change towards the applied stimulus. The effect will be relaxing to the person. This phenomenon is also called frequency following response.
When the brain's state is close to the applied stimulus, entrainment works more efficiently. Thus, when doing a sweep from one frequency to another, the starting frequency should be as close to your current brain state as possible. The sweep speed should be such that your brain's state changes steadily with it, so that the difference never gets very large. In practice, it is difficult to determine your brain state without extra equipment (like EEG devices). However, you can quite safely assume that during the day your brain is in the beta stage (about 20Hz) and you can start the sweep from there. If you are already somewhat relaxed, you can use a start frequency of 15Hz or a few Hz lower.
Stimulating the brain with binaural beat frequencies
The easiest way of applying stimulus to the brain is via ears. Other senses could be used as well, and vision is actually used quite often (often in addition to hearing). However, humans cannot hear sounds low enough to be useful for brain stimulation, so special techniques must be used. One such special technique used is called binaural beats.
If the left ear is presented with a steady tone of 500Hz and the right ear a steady tone of 510Hz, these two tones combine in the brain. The difference, 10Hz, is perceived by the brain and is a very effective stimulus for brainwave entrainment. This 10Hz is formed entirely by the brain. When using stereo headphones, the left and right sounds do not mix together until in your brain. The frequency difference, when perceived by brain this way, is called a binaural beat.
The effect of the audible frequencies used
To get a stimulus of 10Hz, you may use tones of 500Hz and 510Hz, or 400Hz and 410Hz, or 800Hz and 810Hz, or so on. The only requirements are that the tone is heard well enough and that it is below about 1000Hz. Below 1000Hz, the wavelength of the skull is sufficiently small so that the sound waves curve around it.
Reducing sleep needs
Some people have found that half an hour a day of the Theta stage can replace up to 4 hours of sleep.
Treatment of certain mental diseases
Brainwave entrainment is used in treatment of depression, low self-esteem, attention deficit disorder, drug and alcohol addiction and autism, to name a few.
Brainwave entrainment has also been found helpful in alleviating headaches and migraines.
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