Bass Control +3 db: how does it affect 100/50/25 hz?

If I set the BASS Tone Control at + 3 db, what does it mean for 100 hz, 50 hz and 25 hz? I can not find what kind of frequency curve will be applied and at what frequency it starts.
The information helps to prevent overloading the bass-loudspeaker (e.g. port-vented system: +3db at 100 hz, +6 db at 50 hz? That's a lot of energy).