Because half the useful brainwave frequencies (.3-40Hz) are below the hearing range of the human ear (20Hz-20,000Hz), several techniques have been developed to overcome this physical limitation.
This is a quick overview of the different techniques, with a short sample of each.
Note; If you have not already done so, please read ‘What is brainwave entrainment’ first. This will tell you what brainwave entrainment is (and is not), and provides the proper warnings and instructions.
Most audio brainwave entrainment is ‘embedded’ into musical soundtracks to enhance the listening experience. Any full spectrum soundtrack can be used, from a symphony to nature sounds to simple background noise.
Music modulation allows for higher intensity levels than with beats alone.
Monaural brainwave entrainment is a single pulsing beat. It can be heard as a ‘click’ or pulse in the music, created by the convergence of two tones emanating from a single speaker.
Monaural beats are considered to be more effective than binaural beats, however they can more easily interfere with any music they are embedded in.
Monaural beats are used without headphones.
When we hear a sound, we locate the direction it is coming from by detecting the minute the tone differences between each of our ears. Our brainwaves begin to pulse (phase resonance) at the difference between the tones, and using this ‘phase difference’ we detect the direction of the sound.
Binaural beats ‘trick’ this direction finding system by playing a different tone in each ear; for example, if a 300Hz tone is played on one ear, and a 312Hz played in the other, your brainwaves will begin to resonate at the difference between the tones (12Hz, below normal hearing range).
While not quite as effective as monaural beats, binaurals aren’t as noticeable to the ear and improve the listening experience.
Because different tones are played to each ear, headphones are needed for it to be effective. Binaural beats played through loudspeakers become monaural beats.
Often used in combination with monaural and binaural beats, isochronic tones are regular beats of a single tone embedded into a narrow audio bandwidth of the music itself. One frequency band of the music oscillates, leaving the rest of the music untouched.
Isochronic tones are considered the most effective form of audio entrainment, and make for the most pleasant listening experience. If done well, the tones are not noticeable to the ear.
Sound and Light entrainment
With so much of the human brain dedicated to vision, sound and light brainwave entrainment (aka. audio-visual entrainment (AVE), light and sound machines, photic entrainment or mind machines) is far more powerful and much faster acting than audio beats alone. It can elicit a brain response in seconds.
Sound and light brainwave entrainment uses monaural, binaural, or isochronic beats, along with glasses fitted with diodes (or a computer screen) that flash in time with the audio beats.
Sound and light entrainment is quite forceful. Start slow and work your way up, DO NOT overdoo it. Use with due caution.
EEG Active Entrainment
EEG active entrainment is sound and/or light entrainment which changes according to what is happening in your brain at any given moment. The EEG brainwave sensors monitor your brain activity in real-time, and alters the entrainment to suit.
Though the equipment is similar, EEG active entrainment is not to be confused with neurofeedback. Neurofeedback encourages you to change your brain activity yourself rather than ‘pushing’ it there with brainwave entrainment.
Electromagnetic (EM) Entrainment
As with most things, there is an exception to the rule – and that is EM entrainment. Some consider it a form of entrainment; others consider it something else entirely. Either way, it is worth a mention.
Electromagnetic entrainment does not use sound or light. It uses small pulsing electromagnetic fields (at about the same intensity as a large headphone speaker) to directly interact with the neurones.
Brainwaves themselves are electromagnetic in nature. As EM entrainment uses the same method as the brain itself, it is very fast acting (the brain responds in milliseconds). Most importantly, electromagnetic entrainment is region specific, meaning that you can train brainwave frequencies in a certain spot (rather than having to train globally over the entire cortex as with sound and/or light entrainment).
At its best, EM entrainment is used in combination with EEG equipment for real-time monitoring. The EEG can check the brain’s response to each pulse, and shift the frequency as required. It can help ‘un-stick’ stubborn mental patterns, or encourage activity in one area while leaving the others alone. It is quite an advanced tool (see Neurofield).
This is the only type of entrainment that we use clinically.
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