The amount of level you feed into the SubPac from your source device directly affects the bass output of the unit. For example: You have set your phone’s headphone level to just under a quarter way up. You can hear music playing softly through the SubPac but you want to feel more bass. So you turn up the intensity level and quickly run out of room. It’s maxed out. To feel more bass all you need to do is turn up the source.
But now it is uncomfortably loud in the headphones but the bass level is good. The best thing to do in this situation is use headphones with a built in level control. This will allow you to turn down the music to the level you need, but also feel the full range of bass dynamics.