Gamma was dismissed as 'spare brain noise' until researchers discovered it was highly active when in states of universal love, altruism, and the ‘higher virtues’. Gamma is also above the frequency of neuronal firing, so how it is generated remains a mystery. It is speculated that gamma rhythms modulate perception and consciousness, and that a greater presence of gamma relates to expanded consciousness and spiritual emergence.
Hi Ulka, thanks for your compliment on my article. Unfortunately, I haven’t come across any studies or much discussion about the problem with habituation and isochronic tones and how to overcome it. The consensus among experienced users is to regularly change the frequencies and music soundtracks you listen to. Adding music to the tones does change the waveform you are stimulated with, so that’s one of the main reasons why I provide different soundtracks for my isochronic tones sessions. I have released some tracks which use amplitude modulations in the music, instead of isochronic tones. It might be worth giving them a try if you haven’t already. I have them in a playlist on YouTube
Stress can either be perceived as feeling good/positive or bad/negative depending on the context, and the body reacts differently to both kinds. However, where the body isn’t so clever is distinguishing between very serious threats (like being robbed or starved) and events that are stressful but not actually life-threatening. Unfortunately, whether a problem is very serious or not, the body usually has no way of knowing the difference− — anything that causes you to worry, anticipate, regret, overthink or panic can send your stress levels through the roof.
Entrainment is a phenomenon by which some external sensory stimulation synchronizes brainwaves differently than the native rhythm. The most obvious example of this is photic driving – during an EEG the subject will have a strobe light flashed before them at various frequencies. The purpose of this is to see if it will trigger seizure activity. In many normal subjects the brain wave rhythm in the occipital lobes, which is the visual part of the cortex, will match its frequency to the frequency of the strobe light. This specifically is called photic driving, but the phenomenon in general is called entrainment.
A potential and generally desired result of brainwave entrainment is hemispheric synchronization. It refers to a state when the brainwave pattern of the right and left hemispheres become alike. It is said that a person with similar activity in both hemispheres tend to be happier, more optimistic and more emotionally stable and less prone to mental illness. Studies found that increased levels of synchronization are found naturally in people who meditate regularly and people who are very happy with their lives in general.
  That said, you achieve the best results when you listen to the tones in a relaxed, quiet environment, investing your complete attention to the tones and the effect they have on your inner self. Experts recommend that even isochronic tones be heard via headphones to cut out distractions from external noises. The best thing to do is give it your entire, undivided attention, so that you can experience the outcomes quickly and easily.
In 1956, the famous neuroscientist W. Gray Walter published the results of studying thousands of test subjects using photic stimulation, showing their change in mental and emotional states. He also learned that photic stimulation not only altered brainwaves, but that these changes were occurring in areas of the brain outside of vision. In Walter’s words:
When the track is over you can continue to meditate without the help of the entrainment track.  When you are ready to get up, thank your Higher Self for the experience and remove your blindfold, keeping your eyes closed.  Stay seated with your eyes closed for a few moments, then slowly open them and take a moment to let your eyes adjust to your environment’s light. 

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.

^ 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.
“The great neuroscientist W. Gray Walter carried out a series of experiments in the late forties and fifties in which he used an electronic stroboscopic device in combination with EEG equipment to send rhythmic light flashes into the eyes of the subjects at frequencies ranging from ten to twenty five flashes per second. He was startled to find that the flickering seemed to alter the brain-wave activity of the whole cortex instead of just the areas associated with vision. Wrote Walter, “The rhythmic series of flashes appear to be breaking down some of the physiologic barriers between different regions of the brain. This means the stimulus of flicker received by the visual projection area of the cortex was breaking bounds— its ripples were overflowing into other areas.”
Controversies concerning the brain, mind, and consciousness have existed since the early Greek philosophers argued about the nature of the mind-body relationship, and none of these disputes has been resolved. Modern neurologists have located the mind in the brain and have said that consciousness is the result of electrochemical neurological activity. There are, however, growing observations to the contrary. There is no neuro-physiological research which conclusively shows that the higher levels of mind (intuition, insight, creativity, imagination, understanding, thought, reasoning, intent, decision, knowing, will, spirit, or soul) are located in brain tissue (Hunt, 1995). A resolution to the controversies surrounding the higher mind and consciousness and the mind-body problem in general may need to involve an epistemological shift to include extra-rational ways of knowing (de Quincey, 1994) and cannot be comprehended by neuro-chemical brain studies alone. We are in the midst of a revolution focusing on the study of consciousness (Owens, 1995). Penfield, an eminent contemporary neurophysiologist, found that the human mind continued to work in spite of the brain's reduced activity under anesthesia. Brain waves were nearly absent while the mind was just as active as in the waking state. The only difference was in the content of the conscious experience. Following Penfield's work, other researchers have reported awareness in comatose patients (Hunt, 1995) and there is a growing body of evidence which suggests that reduced cortical arousal while maintaining conscious awareness is possible (Fischer, 1971;West 1980; Delmonte, 1984; Goleman 1988; Jevning, Wallace, & Beidenbach, 1992; Wallace, 1986; Mavromatis, 1991). These states are variously referred to as meditative, trance, altered, hypnogogic, hypnotic, and twilight-learning states (Budzynski, 1986). Broadly defined, the various forms of altered states rest on the maintenance of conscious awareness in a physiologically reduced state of arousal marked by parasympathetic dominance (Mavromatis, 1991). Recent physiological studies of highly hypnotizable subjects and adept meditators indicate that maintaining awareness with reduced cortical arousal is indeed possible in selected individuals as a natural ability or as an acquired skill (Sabourin, Cutcomb, Crawford, & Pribram, 1993). More and more scientists are expressing doubts about the neurologists' brain-mind model because it fails to answer so many questions about our ordinary experiences, as well as evading our mystical and spiritual ones. The scientific evidence supporting the phenomenon of remote viewing alone is sufficient to show that mind-consciousness is not a local phenomenon (McMoneagle, 1993).  
Sleep and stress tend to cause a vicious cycle – if you’re stressed, then you can’t sleep, which makes you ill-prepared to handle the stressors of the next day, leading to more stress. To relieve stress before bed, try some relaxation techniques (see below) and disconnect from technology as much as possible an hour before bedtime. To ensure the proper amount of rest (7-8 hours is recommended), set an alarm reminding you to go to bed.
Dealing with sudden stress—a phone call with bad news, a last-minute assignment from your boss, or an argument with your spouse—triggers a cascade of physical and mental symptoms that can be hard to stop. The first thing to do? Pay attention to your breathing pattern, and make an effort to start taking slow, deep breaths as stress relievers. “Breathing can change how we feel because emotions and breathing are closely connected,” says Emma Seppala, PhD, author of The Happiness Track and a Stanford University psychologist who’s done research on yogic breathing. “A revealing research study showed that different emotional states are associated with distinct respiration patterns.” In a follow-up study, participants actually started to feel the emotions that corresponded to an assigned breathing pattern. “This finding is revolutionary: We can change how we feel using our breath!” Dr. Seppala says. Deep breathing gets more oxygen to your brain and may lower levels of the stress hormone cortisol.
When we first use brainwave entrainment, we may not have anything specific in mind that will happen, but we hold a general expectation that “something” should happen. As we begin the process of entrainment we are on high alert looking for any little indication that something is happening. Pretty soon we identify some feeling or twitch or unusual perception. The moment we focus on whatever it is, the act of focusing on it magnifies the thing. Since we were already viewing the situation with an expectation that it was the entrainment that was going to produce some sort of result, we automatically associate whatever our phenomenon is with entrainment.
Many people experienced in using alpha brainwave entrainment report that the state of mind associated with alpha waves is a time when they feel most consciously connected to their subconscious mind. The intense experience of hypnagogic sleep, reported by some people as a feeling of being awake and asleep at the same time, is also associated with alpha brainwaves.
Infra-Low brainwaves (also known as Slow Cortical Potentials), are thought to be the basic cortical rythms that underlie our higher brain functions. Very little is known about infra-low brainwaves. Their slow nature make them difficult to detect and accurately measure, so few studies have been done. They appear to take a major role in brain timing and network function. 
Deep breathing is an easy stress reliever that has numerous benefits for the body, including relaxing muscles and quieting the mind. Breathing exercises are especially helpful because you can practice them anywhere. Perhaps more importantly, they work quickly so you can de-stress in a flash. The ​​​karate breathing meditation is a great exercise to start with, and this basic breathing exercise can be done anywhere to help you reverse your ​stress response, get back to being more proactive (rather than reactive), and face stress with greater resilience.
If you can't spend a full hour in meditation, try the 30 minute Theta Standalone Meditation. This track takes you a little deeper into exploring the Theta frequency than the first Theta track, so it can also be a progression if you have used the first Alpha/Theta combination. If you do have a full hour for Theta, use the 60 minute Theta Standalone meditation.
Brainwaves, or neural oscillations, share the fundamental constituents with acoustic and optical waves, including frequency, amplitude and periodicity. Consequently, Huygens' discovery precipitated inquiry[citation needed] 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.[16][17][18][19]