Like this
Target Level = 75 dB
target level 75 db.jpg
Target Level + Low Pass Filter (Subwoofer Cutoff) @ 80 Hz
subwoofer cutoff 80 hz.jpg
This House Curve adds an 8 dB rise from 80 Hz down to 30 Hz.
house.jpg
Target Level + Low Pass Filter + House Curve = Target Response
house curve +8.jpg
Filter your measured response to hit the target.
predicted (Custom).jpg