Peavey's spec sheet for the 18" low rider say that for a 9 cu ft box it should have two 6 " vents 12" long, it also states that the inside ends of the vent should have a minimum distance of one vent diameter from any interior wall of the enclosure. I have read in other places that there should be a minimum distance from the speaker of two times the vent diameter. I went exactly 6" from everything on the vent and the numbers don't work for a 9 cu ft box. I would need about 2500 cu inches of bracing to offset the size of the box based on those rules. I have looked at other pictures of boxes and they do not seem to adhere to any vent diameter guidlines, some next to the box wall, some next to the speaker. Other vent locations are an option but i have already cut the vent and speaker holes on 3/4" oak plywood. any suggestions? Am I interpreting the diameter rule wrong?