After a lot of work, learned a ton, designing and tinkering, I'm finally happy to present the LittleJet speakers!
(Italian language, but you can skip to 5:39)
(how everything fit inside)
(the final back design)
*** Sine sweep full spectrum, recorded with Spectroid APP on a Honor8 smartphone and built in microphone at 50cm far (see the red line; not smoothed) ***