How does manufacturers figure out what is the best tuning frequency of their subwoofers? I looked at the specs of various companies and they all tune their boxes to different frequencies. Even the same speakers from a same company changes the tuning frequency from their 8 ohm model versus the 4 ohm model. Does it have to do with the resonant frequency? What is the general rule for the best sounding frequency to tune your box to and what is the frequency for the loudest.