The intensity level you use may depend on several things, including earbud fit, personal comfort, type of music, and signal quality, to name a few. The Intensity levels range from 2 to 25, and there is no magic number. Many users find a stronger signal at a lower intensity in Formula Mode and Ambient Mode. This is due to the signal processing that occurs in Audio Mode.
Every person will experience NERVANA differently. We suggest starting at the lowest intensity level and gradually increase the intensity during the first few minutes of use. You will find that there is a “sweet spot” between two levels -- the lower level being just right and the higher level being a little less comfortable.