Rick, just for the sake of technical accuracy, those controls aren't actually gain controls, even if some manufacturers use that term. Amplifiers, including those in subs, have a fixed gain, typically around 30dB, which increases the incoming voltage on the order of 25-30 times. That doesn't vary. What is varied by that loudness control(which is a variable resistor)is the proportion of the incoming voltage that is sent into the amplifier to be subjected to the fixed gain. At the highest setting essentially all of the incoming voltage is let through to be amplified, while at the lowest setting nearly all of the incoming voltage is blocked.
