When the two different sounds are heard, the brain tries to find the middle ground between them. (“www.chriscade”) “For instance, if you play a sound at 100hz in one ear, and play a sound at 108hz in the other, the brain will make the middle sound: 104hz.” (“What Are Binaural Beats? How It Was Discovered? – Binaural …”)
This is what is known as frequency followed response. “The brainwaves want to follow the sound and match it.” (“What Are Binaural Beats? How It Was Discovered? – Binaural …”) This process is called entrainment.