Understanding the gain control on a powered subwoofer.
Why is a gain control needed?
The gain control on a home audio subwoofer allows us to calibrate the bass levels produced by the subwoofer to match the output from the speakers in the system. This will ensure optimal system sound quality.
A gain control and a volume control are the same thing---right?
No. While adjusting them can result in similar results(increase or decrease in volume) the gain control functions differently. A volume control adjusts the output levels. A gain control adjust the output levels *relative* to the input levels. That is an important distinction.
The gain control position is an indicator of how "hard" the subwoofer is working in the system---right?
Incorrect. The gain knob can be set very low and the subwoofer may be working at its maximum limits. Conversely, the gain control can be set very high and the subwoofer may be coasting along and never even approach its maximum output limits. And when you see someone say/post "this subwoofer is very powerful, I only have my gain control set to 25% and the bass over powers the entire room". this really tells you nothing in regards to the subwoofer capabilities. Well, it may tell you it has a very sensitive gain control but that's about it.
At the risk of over simplifying a bit, all the gain control really does is control the sensitivity of the input (RCA jack or XLR) jack on the subwoofer. By adjusting the gain control you are adjusting the amount of bass produced by the subwoofer RELATIVE to the input signal strength your receiver/processor sends it. The maximum output capabilities of the subwoofer never change. There is no "correct" setting for gain controls. You should simply adjust them as needed to ensure proper bass levels during your calibration process.
Power Sound Audio