What I'm trying to find is, proof that ACOUSTIC phenomena is producing ELECTRICAL entrainment in the brain. I have always found this conversion (?) a bit dubious, and it seems like a simple matter to hook people up to EEG while doing Holosync, so thus, there would be science of it if this really worked. I am not a closed-minded person. I use holosync regularly in zen meditation. I just don't know if it is actually entraining my brainwave, or just placebo trance and relaxing sound effects, which is not as spiritually or scientifically interesting lol. I'm not sure why NONE of the material on binaural beat entrainment EVER focuses specifically on how/if/proof that electrical entrainment is produced acoustically. As shown in this video, I get the metaphor, the analogy, of how out of tune notes acoustically produce an acoustic beat frequency. But then, say we had a trombonist on either side of a copper wire, and they played 10 cents off of one another in frequency. You are suggesting that the copper wire would resonate ELECTRICALLY (!!?) with a voltage pattern at the acoustic beat frequency which is the difference between the two trombone notes? HMMMM!  You see how dumb it sounds when I put it that way, but then, I guess that's sort of kind of similar to how electric guitar pickups capture vibrating strings and convert it to voltage? If only anyone in the world knew about acoustics, meditation, and the human brain all at once! But, the reason I remain so skeptical, is that again, it just seems like these are not difficult science experiments to perform. Maybe. I'm no expert on all three of these topics.
It's like any sense. Sight, smell, etc... It all happens inside the brain.

The process of how, exactly, the little hairs of the human ear convert vibrations into signals that go down the auditory nerve is well documented ... but I think I may not be understanding your question.
unThinkMe