Think about it for a moment...your mind is at work all day, every day. Every decision you make, every challenge that you face, every moment you go through in life, your mind is your constant companion, and it can be your best friend or your worst enemy. Your mind is something you need to take good care of, because your quality of life is directly related to your "quality of mind".
The mechanism for this is that when your eyes or ears are exposed to a particular frequency of pulses or beats, the thalamus first distributes this information to the entire brain, including the visual and cerebral cortex where neural activity begins to synchronize to the incoming frequency, producing hemispheric synchronization and a balance of brainwave activity across the brain.
Beware simple answers to complex problems, or easy methods for accomplishing difficult goals. If you combine this maxim with the advice to be skeptical of any claims that are being made in order to sell you something – then ironically you have a simple method (perhaps I should call it an “elegant” method) for protecting yourself from most scams and cons. Actually the application of this combination of maxims can be complex, but what it does do is trigger doubt and skeptical analysis. (And to be clear I am not saying that all simple solutions must be wrong – you should just beware them, meaning your skeptical senses should be tingling.)
Just so, when you reach a state of meditation you don’t “keep digging”, so to speak. The hole has been dug. All that digging has done what it was meant to do. Once your technique has gotten you into meditation, STOP DIGGING! You’re there. If you keep digging you will frustrate your ability to remain in meditation for any significant period of time. Only resume your chosen technique if and when you slip out of the meditative state. If you’re human then you WILL slip out of that state again and again. Don’t worry about that. That’s how the process works for all of us mere mortals.
Most of all, don't feel bad if you fall asleep. Your brain is still receiving many of the benefits of entrainment while you sleep through the audio tracks. In fact, many people report better, more restful sleep when they use brainwave entrainment to help them fall asleep. However, I recommend that you do not go to sleep with your brainwave track set to repeat, as that can be too much stimulation for the brain.
But we don't need any studies to tell us that different people can listen to different kinds of music and be affected. A lot of people who work out have a workout playlist on their iPod that keeps them energized. Some people listen to certain music to help them fall asleep. The Muzak company has built an industry on relaxing music that will keep people in the mood to shop. Music does affect our mood, and so we already have every reason to expect binaural beat recordings to produce the same effect. Different people may find certain binaural beats to be relaxing or energizing. But, we've never found any reliable indication that a binaural beat's connection to our brain is any deeper or more meaningful than any other music track. We do know for a reasonable certainty that specific claims made by most sellers of binaural beats are not credible, and that there is no reason to think that the effect they're claimed to produce will work for you.
With regard to listening without headphones specifically, you might find it irritating if you are someone who suffers from motion sickness, depending on how the track is created. If you were listening to binaural beats, they really need headphones to work properly. If you are in a room and closer to one speaker you may not even hear binaural beats properly, and if sitting off centre in the room generally, that may have unsettled you if you have motion sickness as the tones try to form a beat in your head. If it was just a standard isochronic tones theta track that shouldn’t be irritating if you have motion sickness.
Alpha is the next level down, between 8Hz - 12Hz, corresponding to being awake but deeply relaxed. It can be a little confusing that Alpha is lower than Beta, but it is named that way because Alpha was the first brainwave "discovered" (identified) by Hans Berger in 1929. Meditating in this state is very relaxing and most people find it very easy to become entrained in this frequency.
Brainwaves, or neural oscillations, share the fundamental constituents with acoustic and optical waves, including frequency, amplitude and periodicity. Consequently, Huygens' discovery precipitated inquiry into whether or not the synchronous electrical activity of cortical neural ensembles might not only alter in response to external acoustic or optical stimuli but also entrain or synchronize their frequency to that of a specific stimulus.