There are three main methods currently used for brainwave entrainment: Binaural Beats, Monaural Beats and Isochronic Tones.
Binaural beats are the oldest and most widely used technology. Discovered in 1839 by Heinrich Dove, but it wasn’t until 1973 when Gerald Oster wrote “Auditory Beats in the Brain” that scientific research on binaural beats erupted. Our brain produces different types of brainwaves. The frequencies of these waves range from Delta waves (0.5-4 Hz) all the way to Gamma waves (40 Hz+).
However, human ears are only able to pick up frequencies between 20 Hz – 20,000 Hz. Since our ears can’t grasp frequencies below 20 Hz, binaural beats work by fooling our brain.
How? When you listen to binaural beats with headphones, each ear is introduced to a different frequency. When you hear these 2 different frequencies, your brain reacts by perceiving the difference, called a third auditory beat or binaural beat which can then be used to change your neural rhythm.
For example, if you play 30 Hz in one ear and 25 Hz in another ear, your brain will perceive another auditory beat of 5 Hz. You subtract one frequency from the other: 30 Hz – 25 Hz = 5 Hz.
Brainwaves and brain states impact each other in a type of “feedback loop”. That means, when you introduce a sound which your brain picks up as 5 Hz (as in the example above) for a certain period of time, you trigger your brain to create that frequency (in this case a Theta wave).
Headphones are required for this method. Some people get headaches when wearing headphones.
Monaural beats are combined into one sound before they actually reach the human ear, as opposed to formulated in part by the brain itself, which occurs with a binaural beat. In order for the brain to hear and interpret monaural tones, the different elements involved must be of the same frequency (for instance 50 Hz in your left ear and 50 Hz in your right ear).
Although both types of tone are thought to be effective in entrainment therapy, monaural is a bit more flexible in that it doesn’t require the use of headphones in order to be effective.
In a 1973 issue of Scientific American, Dr Gerald Oster noted that Monaural waves create a far greater entrainment effect than binaurals. The benefit of listening to monaural beats is that the body can absorb the sound (up to a certain depth), whereas binaural beats listened to only with headphones are only ‘heard’ by the brain.
Isochronic tones are regular beats or pulses of sound of the same tone, with silence in between each pulse or beat. Similar to monaural beats, the beat is heard outside the brain, but it is not the result of an interference pattern between two different sounds. The same frequency of tones is output in each speaker and headphones are not required.
Isochronic tones are more pronounced than binaural or monaural beats, and as such produce arguably the strongest brainwave entrainment benefit.
Which Method Is Most Effective?
Studies that have compared the effectiveness of the three methods generally agree that each have their advantages and disadvantages.