Binaural Hearing enables us to locate sound. Since our ears are positioned in opposite directions it takes different times for the same sound to travel to each of our ears.
Even though the time difference is only a fraction of a second, our brain measures the different times and translates it into distance and direction.
Our eardrum or tympanic membrane is the small skin inside our ear separating the outer ear from the middle ear. This eardrum picks up sound waves and transmits them to the inner parts of the ear. If one eardrum is damaged the person becomes deaf in that ear.
A sound is a vibration in the air. These sound vibrations are measured in Hertz (Hz) or cycles per second. Humans can hear sound frequencies from 20 Hz to 20.000 Hz, but the human hearing range diminishes with age.
The Hearing Range can of course vary from person to person. Although we cannot hear them, we can actually feel sound vibrations from 4 to 20 Hz, for example with a hand on a speaker.
Most animals have binaural hearing but at different hearing ranges. Just think of a dog whistle. It is outside our hearing range but pefectly audiable to any dograce.
Here is a comparison of the hearing ranges of different animals:
The human brainwaves have been measured between 0,5 Hz to 30 Hz. A person is considered clinically dead when the brain stops emitting brainwaves.
If you would like to influence your brainwaves with sound you would have to trick the brain to make it respond, since the frequency of brainwaves are outside the human hearing range.
Because of binaural hearing and the way our brain is structured into to two main halves, the effect of binaural beats is possible. As you know our brain is cross wired, the left brain controls the right half of the body and the right brain the left half of the body. Equally that applies to the ears.
When the brain perceives binaural beats it actually creates two standing waves in each hemisphere, and these standing waves entrain the brainwaves. With brainwave entrainment we influence the brain to the desired frequency.
If you would like to relax you need to stimulate the brain with binaural beats to the alpha brain wave state, the relaxed state just before you fall asleep or during a light sleep stage.
Even when a person is deaf binaural beats can work. By putting the headphones with the binaural recordings behind the ear, the sound waves travel to the brain through the scull and entrain the brain just the same.
A thorough explanation about the functions of the ear you can find at this excellent web page www.cyberphysics.co.uk written by a British teacher for students: Well written and easy to understand