Brain waves are electrical activity patterns caused by the neurons of the brain communicating with each other. Brain waves can be detected using sensitive medical equipment such as an electroencephalogram (EEG) monitor. Brain waves provide an indication of the mental state of an individual. In other words, the appearance of brain waves is directly connected to what a person is doing, thinking or feeling. The different Brain states are: Gamma, Beta, Alpha, Theta, Delta. You have your own unique brain wave patterns that function habitually. Some of these brain wave habits are useful, and others need some fine-tuning. When your brain is functioning efficiently, your brain waves are “in sync” with your activity, but stress or lack of sleep can interfere with this natural harmonious relationship. To restore this harmony, at Gaia Meditation, we have developed a wide range of free audio programs, including meditation music, relaxation music, sleep music and plenty other Sound Healing programs.
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.
I wouldn’t personally recommend listening to delta wave frequencies for depression, so I’m not sure who advised you to do that? People with depression usually have a higher ratio of theta and delta wave activity, so I would normally recommend listening to high alpha wave and low beta wave frequencies, to help balance things. I have some 10Hz alpha tracks for serotonin release, which you can try for free on my YouTube channel here: I also recommend you give these SMR (low beta wave) tracks a try: I hope that helps.
Monaural beats have similarities to binaural beats, but the two separate frequencies are delivered through a pulse pattern and mixed before they reach the listeners ears, resulting in the advantage of being audible without stereo headphones. However, using stereo headphones intensifies the effectiveness of monaural beats and is recommended for the best effect. 
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.
However, those with ASD are sometimes also diagnosed with ADHD. Although they are different conditions, some of the symptoms can be intertwined, which it appears may be the case with your grandson. So I would start by trying out my tracks for ADHD. You can try those out for free on my YouTube channel and I’ve put them together in a playlist here: The corresponding MP3 versions for those tracks can be found on my site here: I hope that helps.
Theta brainwaves in the frequency range of 6 to 9 hertz are known as thalpha waves because of their proximity to alpha waves. They are seen during states of high suggestibility, during hypnosis, and during paranormal experience and are also connected to an increase in human growth hormone (HGH) levels and higher blood flow to the brain. Theta brainwaves sit between the realms of the subconscious and conscious mind, making them an especially useful brainwave state for developing creative thinking, working through emotional problems, and integrating subconscious and conscious experience. 

Isochronic tones are the newest technological advancement in the field of brainwave entrainment. Isochronic tones are regular beats of a single tone. In fact, an isochronic tone is a tone that is being turned on and off rapidly at regular intervals, creating sharp and distinctive pulses of sound. This effect called “Amplitude Entrainment” tends to excite the thalamus and causes the brain to generate the same brainwave frequency (“frequency following response”) as the tone. The thalamus, vital structure lying deep within the brain, has multiple important functions: it is involved in sensory and motor signal relay, and the regulation of consciousness and sleep. Therefore, the use of isochronic tones is a very effective way to induce a desired brainwave state.

Wouldn’t it be a blessing if you could find a way to move through each day with a greater sense of peace and harmony, with heightened creativity and intuition, with a sharper intellect and a more positive outlook? For many people today, the deep, effortless meditation that brainwave entrainment provides is the key to a more fulfilling, peaceful and successful life.
After you fully understand the above principles, the next source of poor results to consider arises from faulty expectations and misunderstandings about what meditation and brainwave entrainment are, and what the experience of either one of them is like. Meditation and Brainwave entrainment aren’t synonyms but the misunderstandings about them do have some overlapping areas. Some misunderstandings are common to both while some are unique to one or the other.
Given that brainwaves control and connect such a vast range of human experience from thought to feelings to actions, it is easy to see how the deliberate control of brainwaves can affect mood, behaviors, motivation, and even physical health. Brainwave entrainment is a safe, simple, and scientifically proven method for quickly guiding the brain into a beneficial brainwave frequency to facilitate healthy sleep, lower stress, heal emotional problems, and improve physical health.
The mantra technique as taught by Michael at Project Meditation is an excellent example of an outward technique. Since the vast majority of people have somewhat active minds, this mantra technique is a good bet for most of us. Even mantra techniques have some differences. Some require rigid concentration while others are more relaxed, such as Michael’s technique. There are some that use chanting which is helpful for a person whose mind is hyperactive.
Slightly higher-frequency entrainment can lead to hyper suggestive states of consciousness. Still higher-frequency EEG states are associated with alert and focused mental activity needed for the optimal performance of many tasks. Perceived reality changes depending on the state of consciousness of the perceiver (Tart, 1975). Some states of consciousness provide limited views of reality, while others provide an expanded awareness of reality. For the most part, states of consciousness change in response to the ever-changing internal environment and surrounding stimulation. For example, states of consciousness are subject to influences like drugs and circadian and ultradian rhythms (Rossi, 1986; Shannahoff-Khalsa, 1991; Webb & Dube, 1981). Specific states of consciousness can also be learned as adaptive behaviors to demanding circumstances (Green and Green, 1986).  

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]