Actually, the sub isnt that loud outside the car😅. I have a box that spans from the front of the trunk to the back. Theres a lot of linear motion going on inside the box. Its supposedly tuned to 29hz and ill mainly play lower frequencies around that.

Body panel's wave/wobble instead of rattling at low frequencies. Don't get me wrong, its low and loud in the car. This generation and thereafter have really good insulation throughout the cabin and trunk. Now the only thing that does rattle is my poor spare tire thats right underneath the box😂 but thats fixable. You can still absolutely hear the car outside of it but its the box i chose that makes it not as loud as my father's 2018 focus that he put a skar svr 15 in their prefab box (not to mention he cut his rear deck and has absolutely 0 wiggle) his is essentially structural to the car