yes, tune to your net volume. Then add all the additional volumes to get your gross box. I assume you're using WINISD, or something similar? Keep in mind that you'll get close but it's never exact. It really does not matter too much as long as you're pretty close...it will sound good. I used Alpine's recommended sealed set up for 2x12'' new type r's, and I love it. I needed space so I decided to go sealed, but I think it's as loud or louder than my previous 3x12" Infinity's in a 4 cube, big port box with similar power. This box is only 1.7 cubes gross internal. Anyway, let me know how it works out.

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2004 300M SPECIAL
Alpine CDA 9833
Alpine Pxa-h701
Alpine Rux-c701
Rockford fosgate p400-4
Rockford fosgate p4004
Hifonics BX 1205D
JBL c608 GTi
JBL p963
Infinity 2.5" center channel
Alpine type R 12"(2)
200 amp alternator
yellow top battery
0 awg power and ground (welding cable) 300 amp anl fuse
all active SQL set up with 2000 watts rms