There are 3 variables to consider
These variables can greatly effect the quality of the SubPac experience.
Using the straps there are 3 positions (high, medium and low) that the SubPac can connect with your body. The bass is transferred and interacts with the air and water inside your body so it is important to find the right feel and pressure for yourself. Once you find a good placement where all the low frequencies feel equal, don't change it. A good indicator of the right placement is if you feel the lower notes towards the seat and the upper notes towards the shoulders. Sweeping through the frequencies with a tone generator is a good test of this.
The S2 works best with firm chair backs with little padding. The chair, SubPac and your body are all interacting with each other so its also best to experiment until you find the right combination.
This has the most effect on the experience. A low input level (quiet headphones) will result in higher intensity knob settings. Sometimes in order to balance this, users will find themselves in the 65 to 75 percent area on the intensity knob. This spot on the dial is the beginning of the ramp to full intensity that is meant for either really strong intensity or recordings with weak bass. Playing material at full scale with little dynamic range at this setting can be difficult to adjust. It's better to recalibrate with a little more input and a little less intensity in this situation. Follow this link to the calibration file http://thesubpac.com/download/subpac-guided-calibration-file/