Suggested boxes are something like this based on testing and data thusfar : X-10 : Sealed – 0.75 to 1.0 Ported – 1.25 to 1.75 X-12 : Sealed – 1.0 to 1.5 Ported – 2.25 to 2.75 X-15 : Sealed – 2.0 to 3.0 Ported – 3.5 to 4.5 X-18 : Sealed – 4.0 to 6.0 Ported – 5.0 to 7.0