When you hit a tuning fork, tuned to a particular sound frequency such as the note B, and hold it close to the strings of a guitar, you will notice that the B string on the guitar will vibrate because it has entrained on to the same frequency of the tuning fork. Interesting enough, the other strings will not vibrate. Only the one with the same tuning as the tuning fork.
It may be that you had the volume too loud, but I would expect you to hear the effects of that straight after you’ve stopped listening, not on a day you haven’t used them. It might be something similar to muscle memory, where you suddenly remembered the sound and sensations it gives you as if you were hearing it again. I don’t know how long you’ve been using this type of thing for, but maybe it’s something that will settle down and disappear once you become more accustomed to the sound.
This research investigates the brainwave entrainment process and aims to demonstrate the usefulness of such an approach within the framework of cognitive performance improvements. In the introductory part the theories regarding the neurophysiological structure and the psychological processing of the cognitive system are discussed, for each of their components that are considered to be relevant for this research. The hypothesis states that the stimulation with binaural beats and stroboscopic light, synchronized at 10.2 Hz frequency, will produce a positive change in cognition. The research variables are the cognitive performance (the dependent variable) and the brainwave entrainment (the independent variable). The brainwave entrainment program consists in the synchronized application of Alpha binaural beats and stroboscopic light, at a 10.2 Hz frequency, in a 30 minutes long session. The difference was made by the stroop effect based exercise that was used as a frame. There were 60 participants, divided into two independent samples. The two independent samples t test for the means differences was used in the statistical analysis. The obtained results by evaluations and by statistics confirmed this research's hypothesis, stating that the stimulation with binaural beats and stroboscopic light, synchronized at 10.2 Hz frequency, will produce a positive change in cognition.

That all said, we are all different and have our own different limits. So I generally advise that you just be aware of how you are feeling, and if you feel like you are getting a bit fatigued from it, it’s probably time to stop or at least take a break. When listening over long extended periods, I recommend that you keep yourself well-hydrated. Your brain needs a good supply of water to function well, especially if you are studying hard and increasing your brainwave electrical activity.
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:

Binaural beats are auditory brainstem responses which originate in the superior olivary nucleus of each hemisphere. They result from the interaction of two different auditory impulses, originating in opposite ears, below 1000 Hz and which differ in frequency between one and 30 Hz (Oster, 1973).For example, if a pure tone of 400 Hz is presented to the right ear and a pure tone of 410 Hz is presented simultaneously to the left ear, an amplitude modulated standing wave of 10 Hz, the difference between the two tones, is experienced as the two wave forms mesh in and out of phase within the superior olivary nuclei. This binaural beat is not heard in the ordinary sense of the word (the human range of hearing is from 20-20,000 Hz). It is perceived as an auditory beat and theoretically can be used to entrain specific neural rhythms through the frequency-following response (FFR)--the tendency for cortical potentials to entrain to or resonate at the frequency of an external stimulus. Thus, it is theoretically possible to utilize a specific binaural-beat frequency as a consciousness management technique to entrain a specific cortical rhythm.  
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.
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The phenomena of brainwave entrainment was first described in the scientific literature in 1973 by Gerald Oster in results published in an article in Scientific American entitled, “Auditory Beats in the Brain”. He showed that a specific brainwave could be induced when a person heard two separate, but closely related, sound frequencies, one in each ear. He discovered that when the frequencies heard by each ear differed by about 10 hertz, the brainwave pattern of the person hearing the sound would synchronize to the difference between the two frequencies. For example, if the person heard a 410 hertz sound in one ear and a 400 hertz sound in the other ear, their brainwaves would stabilize at the difference between the two, or 10 hertz. This technique is called binaural beats, and it is a fundamental principle of brainwave entrainment methods.
All of this is entirely understandable, even somewhat predictable. Unfortunately, it quickly becomes counter-productive. Such experiences, while having a certain feeling of solidity to them, are largely the product of our desires and expectations. Did your face get flushed? One look in the mirror confirms it did. Was this caused by the entrainment? No, it was not. It was the result of what was sought after and what was expected or even hoped for.
When stress overwhelms your nervous system, your body is flooded with chemicals that prepare you for “fight or flight.” This stress response can be lifesaving in emergency situations where you need to act quickly. But when it’s constantly activated by the stresses of everyday life, it can wear your body down and take a toll on your emotional and physical health.
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Binaural beats require two separate tones from two sources that are combined inside the listener’s brain to form the target tone. The lower frequency sound is called the carrier tone, and it is combined with a higher frequency sound known as the offset tone. Because of this, binaural beats must be listened to with stereo headphones or the effect is lost. Binaural beats create a hypnotic effect, but they are not the most effective tool for brainwave entrainment, and binaural beats are often ineffective for people with hearing loss.
Now you are ready to experience Delta with the Theta & Delta Deep Meditation tracks. These two tracks work together the same way the Alpha/Theta recordings do. If you have a full hour, definitely use both of these tracks together, starting with Theta Deep Meditation first. The combination of these two tracks is extremely powerful and will give you maximum benefit to your mind, body and emotions.

I haven’t seen any research relating to using brainwave entrainment/isochronic tones and bodybuilding, so I’m afraid I don’t know how effective it would be to help with that. I have a few different tracks for increasing energy but I recommend this 1-hour track, which would fit better than my shorter tracks for a training session: https://www.mindamend.com/shop/energy-and-motivation/high-energy-builder/. The effects from these tracks are mainly felt while you listen to them, so I recommend listening to the energy tracks while you are training/lifting weights etc. I don’t currently have any tracks to help trigger the testosterone hormone.

Stress is a significant individual and public health problem that is associated with numerous physical and mental health concerns. It is estimated that between 75% and 90% of primary care physician visits are caused by stress-related illnesses (2). Cardiovascular disease, obesity, diabetes, depression, anxiety, immune system suppression, headaches, back and neck pain, and sleep problems are some of the health problems associated with stress (4,8). These conditions are some of the most burdensome health problems in the United States based on health care costs, the number of people affected, and the impact on individual lives. Extreme levels of stress were reported by 22% of respondents from the 2011 Stress in America™ survey, and 39% reported that their level of stress had increased during the past year (3). More than 80% of the survey respondents at the WorldatWork Conference in 2012 reported that stress moderately or significantly contributed to their health care costs (6).

Maybe a favorite popular song, a certain piece of Classical music, a raucous dance beat, the pulse of Reggae, Indian, or African drums, or the chanting of Gregorian or Tibetan monks, but you probably know how the sound of music, drumming, or chanting is capable of transporting you into an altered and joyous state of mind and uplifting your spirits.

These brainwaves are actually a bit of a mystery. They’re the highest frequency you can achieve, but scientists are a little dumbfounded by them. Unlike the next set of brainwaves (Alpha and Beta), Gamma brainwaves don’t’ really translate to feeling active and alert. Rather, what’s been discovered is that in Gamma, neurons are firing so harmoniously, that people often feel like they are having a spiritual experience. This brainwave state has been associated with expanding consciousness and understanding the value of universal love and harmony.
Isochronic tones work just the same in delta as they do in alpha, theta and beta and they are widely used in the brainwave entrainment community to help people sleep. Like you, I’ve also seen some websites saying they don’t work in delta, but it’s a bit like the game of Chinese Whispers, where someone makes a comment and then after it gets passed around and shared a lot the message gets distorted and appears to be a fact. I don’t know of any scientific reason why they wouldn’t work in delta. I remember some people talking about this on a brainwave entrainment forum many years ago. They were saying they found isochronic tones a bit too abrupt for using to help them sleep and they preferred binaural beats, as they thought they were a more soothing sound. That was just a personal preference shared by a couple of prominent forum members at the time and some people then took that as a fact for everyone. That’s where I think that belief originated from.
If anybody would like to look over the scientific evidence concerning brainwave entrainment and isochronic tones, I’ve done a lot of research over the years which I’ve collected at the PubMed website of NCBI – a branch of the National Institute of Health – that provides access to a large library of medical journal articles. I’ve made my list public so you can look through the journal articles that were published concerning this topic. Here’s the link: http://www.ncbi.nlm.nih.gov/sites/myncbi/1tmDFOl0XtyA4/collections/51531796/public/. Most of the collection only gives access to abstracts or summaries unless you’re at some kind of educational institution that has a subscription to the particular journal that article is in, but I actually find abstracts really helpful. So have at it, read away. And if your psychiatrist/therapist thinks you’re nuts for feeling better after listening to isochronic tones, just whip out your 82-page collection of scientific journal abstracts written by her peers and give it to her to read. 🙂
John Dupuy is the CEO of iAwake Technologies and travels internationally to teach and inspire on the subjects of Integral Recovery, Integral Transformative Practice, and the use of brainwave entrainment technology to deepen one’s meditation practice and in the treatment of addiction, depression, and PTSD. John is the founder of Integral Recovery® and his book Integral Recovery: A Revolutionary Approach to the Treatment of Alcoholism and Addiction  won the 2013 USA Best Book Award. John also hosts interviews with leading innovators in the spiritual technologies field on Spiritual Technologies 2.0 Live and co-hosts the popular Journey of Integral Recovery podcast.
This depends on how ready your brain is to absorb the impact of the tones and how responsive it is. Most people experience a feeling of relaxation and calm right from the first session. The degree to which you feel these hinges on how well your brain reacts. Use it over a few days and you can experience unmistakable signs of stress reduction and improved clarity of mind. After a while, when you brain gets trained in allowing better communication between the right and left hemispheres, you will sense that the feeling of mental clarity and calm carry forward even hours after a session.
Cortisol is an arousal hormone, stimulating alertness and attention. Cortisol levels rise and fall in connection to circadian rhythms—cortisol levels rise to their peak levels first thing in the morning, just in time for you to be active for the day. Too-high cortisol levels are associated with insomnia, as well as more time spent in light sleep, rather than deep sleep.
The Delta brainwave is experienced by us every night in dreamless sleep. It is also experienced by advanced yogis and monks who can enter the Delta frequency during deep meditation. This frequency assists in both emotional and physical healing, as well as enhanced immune functioning, significant stress reduction, and even anti-aging benefits. The Delta frequency is a terrific way to experience deep repair on the physical, emotional, and psychological levels.
Some research suggests that the benefits from brainwave entrainment can last a lot longer, and still be seen for some time after you've stopped using it.  Study participants have still maintained improved test scores a few weeks after the stimulation had ceased.  Research on the long-term benefits has so far been minimal though, so how long the effects last is still up for debate.

Over-arousal in certain brain areas is linked with anxiety disorders, sleep problems, nightmares, hyper-vigilance, impulsive behaviour, anger/aggression, agitated depression, chronic nerve pain and spasticity. Under-arousal in certain brain areas leads to some types of depression, attention deficit, chronic pain and insomnia. A combination of under-arousal and over-arousal is seen in cases of anxiety, depression and ADHD. more...
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♥  I'm an ADHD high school student and I've found that this sound really helps me to get my homework done. Normally, I would be up very late writing essays and studying for tests because I can't sit down and focus on them, but this helps me to focus and also keeps me awake even late at night so I can continue to work. I love this site and I know I'll use it for a long time!
For example, if a 530 Hz pure tone is presented to a subject's right ear, while a 520 Hz pure tone is presented to the subject's left ear, the listener will perceive the auditory illusion of a third tone, in addition to the two pure-tones presented to each ear. The third sound is called a binaural beat, and in this example would have a perceived pitch correlating to a frequency of 10 Hz, that being the difference between the 530 Hz and 520 Hz pure tones presented to each ear.

I am fortunate to be working with Deepak Chopra, M.D., and Dr. Rudy Tanzi, co-authors of the bestselling book Super Brain, on a technology called Brain Wave Entrainment. Deepak is very well known, but Rudy is an amazingly interesting person as well. He is the Kennedy Professor of Neurology at Harvard Medical School and Vice-Chair of Neurology at Mass General Hospital. Rudy co-discovered three of the four original Alzheimer's genes and today runs the Alzheimer's Genome Project. He also plays the keyboards, including, at times, for Aerosmith. He is kind of a real life "Buckaroo Banzai."
The quickest way to relieve stress is to release endorphins through exercise. An easy way to do this is through shaking and dancing, a form of expressive meditation that loosens your joints as well as clears the mind. It’s one of our favorite techniques to teach in conflict and disaster areas, such as Haiti. Start by standing with your feet shoulder-width apart, knees slightly bent, shoulders relaxed, and shake your whole body for a few minutes (we recommend 7-8 minutes). Then, stop for a minute or two and pay attention to your breathing and physical sensations. Finally, turn on fast music – anything that gets you energized, and allow the music to move you. Don’t feel the need to follow any specific dance moves, just do whatever feels good for you in the moment (it might help to close your eyes). Dance for about 5 minutes, or until you feel satisfied.
The Frequency following response (FFR), also referred to as Frequency Following Potential (FFP), is a specific response to hearing sound and music, by which neural oscillations adjust their frequency to match the rhythm of auditory stimuli. The use of sound with intent to influence cortical brainwave frequency is called auditory driving,[39][40] by which frequency of neural oscillation is 'driven' to entrain with that of the rhythm of a sound source.[41][42]