I am building a box for 2 12" memphis mojos and they call for 4ft^3 each. i emailed tech support and they told me with some xpecs i gave them that a 35(side to side) x 16(top to bottom) x 20 (front to back) box would give me about 6.5ft^3 airspace and the correct port size would be 4.5 x 14(lenth of box top to bottom) and 14" deep tuned to 40Hz. Is this correct? Will that give me the groundshaking bass im not getting with the subs in the sealed box downifiring that i have them in now? THANKS!!!!