I'm trying to design an SPL competition enclosure for a single tempest with maximum SPL at 43-47hz in mind, (tuning frequency of car). I've been crunching numbers in WinISD and Adire Audio but am still undecided on a design. The size range preferred is between 70 and 200 liters. I have two flared 3" diameter vents I can adjust length. The tricky part is the smallest flared port possible is still about 6" from flared tip to tip. So for a box that's 100L, tuned to about 40hz but it asks for a port that's 13cm which is the length of a flared port without a center tube. (am I right?) The other designs such as bandpass 4th and 6th order were interesting but they don't have the option of having the ports plugged for a "sound quality" conversion like a vented sub does. Basically what I'm looking for is a box that has maximum SPL at about 45hz that has the option of the ports being plugged for sealed operation. I guess that another limitation is the minimum size of the flared port which would be a center tube of 0". Any advice or suggestions from fellow bass people would be appreciated. Here's my first design: Box volume = 100L Dual Ports: Length = 13cm (Which is 0" center tube) Res. Freq. = 39.5hz Result 1w/1m = 93db @ 43hz (with a -3db downpoint at 39 & 57hz) Has an 8-10db boost over a 100L sealed box. I still don't know if I should just slightly alter Adire's SBB4 design by decreasing the volume and tuning it slightly higher for a just plain SQ car sub. (SBB4 = 194L tuned to 18.8hz). Do you think I'll be capable of SPLs to enter in a competition? I have a bridged 600 watt amp @ 4 ohms 12V for it. I also have a 1 farad cap, 4 gauge wiring, and the whole back of a Toyota 4runner to work with.