Theta waves have a frequency between 4 and 7.5 hertz, making them slower than more wakeful alpha but faster than the dreamless slumber of delta. Theta brainwaves are the frequencies of nighttime dreams and REM sleep when the brain goes through bursts of activity and eye movement. People also experience theta waves in a state of light sleep, deep relaxation, during meditation and prayer, and when daydreaming. Theta waves produce an experience of inward wakefulness where we become disengaged from the outside world while engaging in inner activity. At the lower frequencies of theta, sleeping states are experienced, and at the higher range of frequency, awake relaxed states are experienced. 
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.
There are many sources of binaural beats on the internet and YouTube to check-out and experiment with yourself – I recommend using headphones for optimal effectiveness. However, like most things, not all binaural beats are created equally (especially if they are free on the internet) and therefore not as effective or enjoyable to listen to. This is why I HIGHLY recommend the binaural beats created by master audio technician, music producer and meditation teacher, Cory Allen – which can be found here:
There are primarily three ways to elicit the frequency following response through an audio: binaural beats, monaural beats, and isochronic tones.  Binaural beats was the first method to be discovered, and has been used since the 80’s, after being first made known and popular by Robert Monroe of the Monroe Institute (the institute is still around today, though Mr. Monroe has passed away).  Binaural beats basically work in this way: one specific frequency/beat is played in one ear, let’s say, 1115 hz., while one slightly different frequency is played in the other at the same time, let’s say, 1120 hz.  What the brain will naturally do while exposed to these two frequencies in either ear is create its own “phantom” beat, that is the difference between the two frequencies.  In this case, it would be 5 hz., which is the frequency of the theta brainwave state.  Therefore, your brain would be led into the theta state.  At the same time, your brain working to combine these frequencies also ends up synchronizing its two hemispheres, and functioning in a whole-brained fashion while the listener is using the audio.

Hemispheric synchronization: Whether it’s optimal or suboptimal to operate in a state of hemispheric synchronization remains unknown. Some speculate there are numerous benefits of brain waves operating in “sync” as a result of entrainment. There may be an increased communication between the right and left hemisphere of the brain – which could improve certain functions. However, it is also important to realize that increased hemispheric synchronization may not be as beneficial as many have speculated.
I’m sorry to hear you’re having these troubles. First off, I disagree with whoever told you it was a good idea to listen to 6 subliminals a day. I suppose I would need more context to better understand. Are these binaural beats or brainwave entrainment audios? If so you are definitely listening too much, and can harm yourself (just as the article mentions above from over-doing it). Even if they are not brainwave entrainment audios, I cannot imagine it is effective or the best idea to listen to so much so often. I would pick one subject that correlates to the most important goal for you and stick with it until you have achieved it. Remember to steer clear of that tempting idea of getting “all that you want for nothing”. Even subliminals are a tool. You still have to use the tool to do the work.
Another small scale study with 30 children were entrained with a starting frequency of 14 Hz and ramped up to 40 Hz. Following the excitatory-based protocol, they were then given a protocol that started at 40 Hz and decreased to 14 Hz over 6 weeks. The results indicated that the children significantly improved in arithmetic abilities based on the WISC-III.
Sound and light are the most popular methods to entrain the mind, yet there are a few other options in our toolbox. Using vibrational energy from sources such as magnets and electricity has been proven to help overcome addictions, depression, and even treat neurological disorders such as Parkinson’s. In this section, we cover these alternative forms of brainwave entrainment.
The basic idea behind the Laxman light and sound technology is that the gentle pulses of light can lead one to the state of mind associated with that particular frequency range. The various pre-programmed “sessions” found in the Laxman mind machine can be used for different purposes, including meditation, stress reduction, accelerated learning, restful sleep, increased creativity, and goal setting.

Brain Wave Entrainment is any procedure that causes one's brainwave frequencies to synchronize with a periodic stimulus (sound, vibration or light) having a frequency corresponding to the intended brain-state (for example, to induce a trance, dreams, sleep or relaxation.) It is also called the Flicker-response because of how staring at a campfire or the flickering of a burning candle can lull you into a state of calmness and serenity. There was an extensive article on this phenomenon by Gerard Oster in Scientific American in 1973. It may sound novel, but in many ways, this is old tech.

You also may find that after pushing yourself really hard, now you have pushed yourself a little too much, and you’re getting into overwhelm. You may want to ride that overwhelm like a wave to where it’s pushing you just a little bit, but not so much that it will push you over the edge and have you take a dive. So, maybe on Saturday, after pushing hard all week, you might decide to put on the releasing tracks. In this way, you can still experience a very deep and blissful meditation, but without all the push from the carrier frequencies and the biofield amplitude.
Jump up ^ Bittman, B. B., Snyder, C., Bruhn, K. T., Liebfreid, F., Stevens, C. K., Westengard, J., and Umbach, P. O., Recreational music-making: An integrative group intervention for reducing burnout and improving mood states in first year associate degree nursing students: Insights and economic impact" International Journal of Nursing Education Scholarship, Vol. 1, Article 12, 2004.
If you find that you are really heavily into overwhelm, you can just turn the volume down and meditate with the biofield amplitudefrom your iPod, CD player, PC, or Mac transmitting a very healing biofield technology that allows you to dig deeper into meditative states without putting your nervous system on edge. Now you are pushing and purifying your nervous system without bludgeoning it.

Meanwhile, the therapeutic benefits of listening to sound and music is a well-established principle upon which the practice of receptive music therapy is founded. The term 'receptive music therapy' denotes a process by which patients or participants listen to music with specific intent to therapeutically benefit; and is a term used by therapists to distinguish it from 'active music therapy' by which patients or participants engage in producing vocal or instrumental music.[37] Receptive music therapy is an effective adjunctive intervention suitable for treating a range of physical and mental conditions.[38]