The reason this rule of thumb is so useful is because there is a huge market for simple answers. A genuine elegant solution (one that accomplishes more with less) is highly valuable in the marketplace. We are used to technology delivering new easy solutions to previously difficult tasks. While most improvements are incremental, there are occasional breakthroughs that transform our lives.
In 1984 medical researcher Dr. Gene W. Brockopp published a paper making several conclusions of audio and visual entrainment (AVE). Such conclusions were that hemispheric synchronization caused by AVE is related to increased intellectual functioning, practiced use of AVE overtime leads to a cumulative effect, and AVE may result in the recovery of early childhood experiences.
Research done under Gerald Oster suggested that binaural beats may be used as a medical tool, especially for diagnosing neurological conditions. In particular, he noticed that untreated sufferers of Parkinson’s disease were unable to “hear” binaual beats but further research indicated successful treatment when the subject was finally able to perceive them at the end of a Parkinson’s treatment regimen. Oster also noted difference in perception in women based on their menstrual cycle, and posited that there may be some connection between the ability to perceive binaural beats and the woman’s levels of estrogen at the time.
A few years ago I was very sick with anxiety. I saw a Psychologist and he recommended the Audio Deep Sleep. I was uncertain at first and falling asleep with the sound sounded odd at first. As I progressed, I became at one with the CD and soon found, if I missed a night I soon missed playing the CD. Over the course of time I have done quite a bit of healing and found I was not using the CD much. Over the past few months I really missed it and found the CD hard to find. It wasn't until I happened upon this site and found the Deep Sleep CD. I played the sample and found myself missing the CD greatly and discovered my brain seemed to miss it just as much. I am grateful to you and just as much as my Doctor has given me my life back to a fair extent, I am am grateful to you as well. :)

^ Trost W. and Vuilleumier P., Rhythmic entrainment as a mechanism for emotion induction by music: a neurophysiological perspective. In The Emotional Power of Music: Multidisciplinary Perspectives on Musical Arousal, Expression, and Social Control, Cochrane T., Fantini B., and Scherer K. R., (Eds.), Oxford, UK: Oxford University Press; 2013, pp213–225.
Besides scientific literature, some authors have written of the promising research on meditation in books targeted for general audiences. One such book, Buddha’s Brain by Rick Hanson, PhD shares the current scientific research and investigations into meditation.[19] Hanson, a neuroscientist and researcher, explains to readers the scientific studies in plain language and discuss the impact of the results. Hanson’s main argument is that positive emotions, like love can be strengthened through meditation in a neuroplastic manner, citing dozens of scientific studies to support this claim.[19] Hanson’s viewpoint is representative of a larger popular movement to study and embrace Eastern phenomena including meditation in the Western world.
I have read something different about theta waves and learning languages. A University of Washington study tested students resting brainwave activity before learning French. They found that students with a higher amount beta/gamma and a lower amount of delta/theta activity were better at acquiring a second language. When you are dominant in theta, that is the lowest and most deeply relaxed awakened state you can be in. I think it would be much harder to really concentrate, fully understand and learn new information while in a theta state, so I would personally consider using theta while studying.
Please note: When you take one earphone out, move it as far away from your ear as possible. With some headphones you may still be able to hear the pulsating sound if the removed headphone is still fairly close to your ear; this is because your brain can still detect the frequency vibration coming from the headphone. In addition, push the earphone that’s still on your ear tightly to your ear, while moving the other earphone as far away as possible.