Based on 8.8 cu .ft. internal

Well four 6" will give you 113 sq. inches

4-6" @ 5.5" long roughly will tune to 64hz this is taking into account there area if put inside the box (flush outside)

4-6" @ 35" long to try to tune to 32hz which may not be feasible, depending on box size

So you need to figure out whether your going for pure spl or daily also, you might be better staying with a rectangle port.

Garett

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RD Audio Dealer
DD Dealer

Aaron's 97 Cavalier Trunk

1 Z1
1 9515
1 Not so good Optima Battery
4 runs total of 1/0

Certifiied:

152.0 Iasca
150.4 Db Drag

Cavalier is being changed to RD equipment, still a single 15" though