i started sanding one enclosure to make it matte black instead of glossy black.
looks way nicer now, also sanded round corners and removes sharp edges.

i also applied the second 4" speaker to the back of the speaker to let it be a temporarily passive radiator.
then i measured the response at 1meter away, and found out that the bass response wasn't exactly what i hoped for.

but that's to be expected with such a small speaker in the middle of a 25 square meter room.
the measure showed a minimal rolloff above 15k when at 1meter distance, nothing too serious luckily.

the lower rolloff was lowered from 200hz to 100hz, but was a more steep one than the original measure (passive radiator effect?)
still, it goes as low 80hz with ease (-6db point) with the temp passive radiator.

overall very pleased with something as tiny as these speakers.

next steps are:
sand second enclosure
wait for the final passive radiators and mount them
screw the terminals in
solder the internal wiring
fill the internals a bit with dampening wool to help with possible resonances.