For music mind you. I’m not talking about hitting numbers on test tones.
If you want to meter super high on a 40 hz test tone, 4 cubes at 40 hz is a good box, but that is way too peaky even on music for me. they will murder a 40 hz test tone though. You should build it both ways man. Test them out and post some vids.
If he is taking cabin gain into effect, that makes sense to me.
You won’t even notice it until you listen to hip hop.
If your going to throw that type of wattage at them, I’d definitely lower the box size some, and do a big ass port tuned in the low 30s. I don’t want to override your box builder here Bobby. Maybe he has done 200 boxes for these specific subs. I’ve done 3, and I’m not the one listening to them every day. I have the Dayton ultimax.