In pro this comes up in "bass managed" speaker placement in ATMOS systems. When you roll out the bass of a small speaker, how much does the total SPL capability change? The answer is you have to measure it. We did so at the ATC factory and it only gains around 1dB total output SPL to use a HP filter (bass management). There exists out there some manufacturers that state massive improvements in SPL when bass managed, I'm not sure how they arrived at these new measurements and conclusions. So I think from a practical standpoint, you'll get a little improvement in total SPL by filtering out LF, but its less than you'd guess.
Speaker relative efficiency/sensitivity when using a high pass filter
Is there a formula/algorithm/rule of thumb for calculating how a speaker's power requirements might change when the lower frequencies are handled by a subwoofer? Specifically for a ported speaker with a supposed frequency response down to 35Hz and an a 89dB sensitivity with a second order crossover at 80Hz. I know it goes down but by how much? I recognize that power requirements increase as frequency decreases but is the difference enough to allow for a less powerful amp? I would think so.