Tell me if I have this right.....

The Low pass slope on the subwoofer is 24dB per octave and I have a crossover at 80Hz. Let's say a 60dB signal across the band (20Hz to 20kHz) is sent to the sub (digital connection). That signal would be 60dB from 20Hz to 80Hz and start sloping down dropping to 36dB by 160Hz, and 12dB by 320Hz. Is that correct?