My owner's manual for my subs lists the ported box should be 2.0cu ft after driver and port displacement with a port size of 4x14" at 33hz. I want to shift the port to 28-30hz, would I just have to increase the overall airspace and change the shape of the port to get to the lower frequency? I am designing a custom ported box for my Boston G5's and I'm worried a 33hz tune won't give me the low-lows that I want. This is my first ported build. All help is greatly appreciated.