Cheap planter pots as speaker enclosures - genius or garbage?

I ran flower pot pods for a season in my old Civic and yeah, they work, but not the way people think. The deadener adds mass wich lowers the resonance a bit, but the pot walls still flex. Mine buzzed against the trunk trim on anything under 80 Hz and I could push the sidewalls in with a thumb even after two layers of tile. It sounded better than nothing, which is a low bar.

I went with MDF rings behind the factory cutouts in my old wagon and honestly the cost difference is nothing. A half sheet of 3/4 MDF from the big box store was maybe fifteen bucks and I had it cut at the store so I only did one screwdriver job with a jigsaw. Traced the stock opening, cut rings, glued them in with construction adhesive, screwed the speakers straight to the rings. Whole thing was one Saturday afternoon including a beer break.

The difference was night and day compared to what you're describing. Before the rings the mids were thin and everything below the vocals just leaked into the trunk and turned to mush. After sealing them to real wood the bass acutally showed up in the cabin and the speakers stopped bottoming out on heavy tracks. Thin plastic pots flexing behind them would undo half of that. MDF is rigid and it stays glued, no buzzes against trim. I get that the pot route costs almost nothing up front, but you spend just as much on deadener rolls and then you're still guessing at the air volume. With a ring and the stock cavity you know exactly what the speaker sees. For a daily driver wanting door speakers that sound like something, wood is the boring answer that actually works.

Yeah the MDF route is the way to go. I did the same deal in my sedan years back, rings glued behind the stock holes, and I went one step further and ran a bead of silicone around the edges before mounting. That sealed up all the air leaks into the trunk and the midbass finally had some punch to it. Took me an afternoon with a hole saw and some clamps while the glue set. Never looked back after that.

On the volume question, you can actually answer it yourself without guessing, since a sealed pod only needs to be a sensible fraction of the driver's specs and nobody eyeballing a planter is going to hit an exact target anyway. Fill the pot with dry rice, dump it into a measuring jug, subtract a rough guess for the magnet and basket, and you have a real number instead of a shrug. That said, in my experiance the bigger variable with these improvised enclosures is cone alignment, because if the baffle isn't flat and centered the surround binds on one side and you get distortion long before the wall flex matters.

Reading this makes me feel better about the planter idea I tried in my old car with a cheap bucket from the dollar store. It buzzed so bad I wrapped it in that rubberized paint from a spray can, helped a little but it still sounded hollow. One thing I never figured out, does the filler material like stuffing or pillow fluff matter in something that small, or is that only for big boxes?

The plastic flex thing killed me for a while too. What actually fixed my cheap bucket pods was lining the inside with fiberglass mat and resin, just brushed it on like making a skateboard mold. Took one weekend, stank up the garage, but the walls went from rubbery to knocking on it like a table. Before that the deadener was doing basically nothing no matter how many layers I stacked.

Only warning I'd give is wear gloves and do it outside, that resin is nasty stuff. If the flower pot shape works for your openings it's worth a shot, otherwise rings are less mess.

Update: skipped the flower pots after reading the first reply about the walls flexing and buzzing. Went the MDF ring route behind the openings, ran a bead of silicone around the edges like the sedan guy suggested, and holy cow the midbass actually hits now. Cost me one Saturday afternoon and half a sheet. shoud've done it that way from the start.