Binaural (two ear) beats are auditory brainstem (i.e., hemispheric) responses from two different sound impulses, each at a different frequency, entering opposite ears, that take the form of a single frequency response sent to the cortex. The frequencies of the presenting waves can be anywhere below 1000 Hz, but the difference between them must be between 1 and 30 Hz (Oster, 1973). When this occurs, the part of the brainstem that integrates auditory stimuli perceives and locks on to (entrains) to the frequency difference between the two sounds.
For example, a frequency of 470Hz and 440 Hz enter opposite ears simultaneously or in close proximity. The difference between the two, 30Hz , is the frequency that is integrated and sent forward from the experience (Oster, 1973). This Frequency Following Response (FFR) is the potential of the brain to follow the frequency of an external stimulus.
FFR give binaural beats their tremendous therapeutic potential. However, it took some years, the marriage of several fields of study, weathering a crisis in one field and the disastrous collapse of scientific knowledge in another, to bring us to where we are today. However, to understand these mysteries a little better, an elementary physics lessons is needed.
Everything resonates (vibrates) at a frequency peculiar unto itself, and humans are capable of hearing from approximately 25 Hz to 19,000 Hz of them, though some hear more at the lower end and some at the upper. The average human voice is 250 Hz, whereas the average man hears at 17,500 Hz and woman at 18,000Hz. Dolphins put out and can “hear” 200,000 Hz. Dogs can detect frequencies as high as 45,000; the domesticated cousins of the King of Beasts, however, weigh in at nearly twice that. The elephant, on the other hand, can pick up sounds only as high as 10,000 Hz but can detect frequencies as low as 5Hz (Henderson, 1996) . Interestingly enough, the elephant puts out a frequency of 3-4 Hz, which not even it can hear. Presumably, elephants and all around them feel this vibration—the shaking of the earth—as the distant herd draws nearer.
As we have seen, binaural beats are the perceived auditory “beats” that are the integration of tones used to alter brain patterns through FFR. “Beat” is a misnomer, however, because there is no actual beat to it. In the “Behavior of sound waves,” Henderson (1996) explains:
“Beats are the periodic and repeating fluctuations heard in the intensity of a sound when two sound waves of very similar frequencies interfere with one another”. The beat is said to “oscillate,” go from zero amplitude to a larger amplitude, back to zero amplitude throughout the pattern, as when a middle C and D are played together on the piano. “Interference” occurs between the loud sound made at the peak on the beat pattern when the waves are apart and the no sound made in the lower area when they are joined. Together the result is the discordant waa-waa sound that is heard when two dissimilar notes are played at the same time.
Another important property is beat frequency, the “rate at which the volume is heard to be oscillating from high to low” per second (Henderson, 1996). This means that if two complete cycles are heard every second, the frequency is 2 Hz. The beat frequency of binaural beats is always equal to the difference in frequency between the two notes producing the beat. But the frequency of 2Hz cannot be heard by the human ear,
But what if the two sounds have frequencies of 256 Hz and 254 Hz . A beat frequency of 2 Hz will result but this cannot be heard. Nor does it need to be, because by now operations have moved to inside the brain where the frequency of 2 Hz will be detected. But as the sound itself is slightly lower than our elephant’s thumping, the human ear is not going to be hearing it. Beats are rare in nature, writes Oster (1973); in nature “sustained pure tones are rare” (p.94). At the same time, we can see how any number of unpleasant beat frequencies might repeatedly reach us during the course of a working day: a heating system, traffic, aircraft passing overhead, the hum of a computer’s motor (Oster, 1973). The ear may not hear the beat, yet it is detected.
The importance of binaural beats is the resulting process within the brain. It is necessary to understand why the two sources of sound must to come to the listener through separate ears. They were first discovered, according to all sources, before the advent of stereo output devices, using tuning forks positioned at each ear by a German researcher, H.W. Dove, in 1839 (Oster, 1973). If this original article was even translated, it appears to have disappeared—but everyone refers to it.
Binaural beats, as we know the science today, was pioneered by Gerald Oster (1973), who saw it as a way to diagnose hearing difficulties and possible brain disorders. His research revived the interests in binaural beats and introduced oscillator output to replace tuning forks. Like much of the research that followed his, it was exploratory; there was no null hypothesis. Yet researchers from many areas with varied interests now began to explore the brain’s response to stimuli, beginning with auditory stimuli. Frequency-following responses most remarkably, could clearly be seen in EEGs; the brain’s frequency followed that of the sound stimulus (Smith, Marsh, & Brown 1975).
Brainwaves, the measurable markers of various states of consciousness, are studied as a part of and are regulated as a function of brain’s reticular formation, which through a complex net of nerves, stimulates the thalamus and cortex (see Fig. 2). This is the RAS or reticular activating system, a large, net-like area of neural connections extending down both upward and downward from the brainstem (Anch, Browman, Mitier, and Walsh, 1988). The RAS terminates near the scalp, where the neural electrical activity makes electroencephalography (EEGs) possible.
