The binaural beat effect is real and well-established in auditory neuroscience. When two tones of slightly different frequency are delivered separately — one to each ear, via headphones — the brain cannot process the discrepancy as two distinct sounds. Instead, it perceives a third, phantom frequency: the mathematical difference between the two. A 200Hz tone in one ear and a 207.83Hz tone in the other produces a perceived beat of 7.83Hz.
This part is not in dispute. It's a documented feature of how the auditory system processes interaural timing differences, first described in the scientific literature in the 19th century.
The entrainment claim — and its limits
The more contested claim is what happens next: that sustained exposure to a binaural beat causes the brain's own electrical activity to "entrain" — synchronise — to that beat frequency, shifting the dominant brainwave state toward whatever frequency the beat is tuned to. Some EEG studies report measurable shifts in this direction, particularly toward theta-range states associated with deep relaxation. Other researchers have struggled to replicate strong effects, and the field is best described as promising but unsettled rather than conclusively proven.
Why theta, specifically
Theta-range binaural beats — roughly 4 to 8 hertz — are the range most associated in the research literature with hypnagogic states, deep meditation, and reports of altered consciousness. It's also, not coincidentally, the range that sits closest to the Schumann resonance's 7.83Hz fundamental.