[pbronez]

If you want to DIY something similar, check out the LXmin and other Linkwitz designs

https://www.linkwitzlab.com/Store/LXmini.htm

[westurner]

In this video, they explain that the bandpass port for letting air out of typically the back of speakers is essential for acoustic transmission including bass; and they made an anechoic chamber.

"World's Second Best Speakers!" https://youtube.com/watch?v=EEh01PX-q9I&

TechIngedients also has a video about attaching $6 bass kickers to XPS foam to make flat panel speakers about as good as expensive bookshelf speakers.

"World’s Best Speakers!" https://youtube.com/watch?v=CKIye4RZ-5k&