So, what we’re doing is combining these two parts, the awakening of complete stillness and deep relaxation with the rhythmic sounds, and embedding all frequencies within the music from right at the upper limits of human hearing to the lower limits. There is multi-level entrainment within Journey—I’ve layered in everything I know about audio brainwave entrainment into this track. 
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.
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.
The functional role of neural oscillations is still not fully understood;[6] however they have been shown to correlate with emotional responses, motor control, and a number of cognitive functions including information transfer, perception, and memory.[7][8][9] Specifically, neural oscillations, in particular theta activity, are extensively linked to memory function, and coupling between theta and gamma activity is considered to be vital for memory functions, including episodic memory.[10][11][12]