Been looking around at speakers and soundbars a bit a came across Audiosmiles LMB v3 Kit. Some seriously impressive performance (58 Hz - 20 KHz -6dB) from a such a small box (120 x 205 x 135 mm WHD). You can read a pretty good review with analyisis at Audioholics.
Looks like their has been a few versions since a Kickstarter in 2016 and there are other interesting projects including the assembled LMB v3 on the founder, Simon Ashton’s website. He has also written about his latest v3 design in two papers (LBM White Paper & Port Design Study).
Interestingly enough, after reading the built guide and with a bit of googling around, it would not be hard to knock up something similar (or more suited to a particular need say a passive speaker arrangement or soundbar or slightly bigger drivers to extend the range/power) as the drivers are Dayton Audio ND91-4 and Peerless by Tymphany PMT-30N18AL04-04 tweeter (actually listed on my local distributor as a full range which is like why it needs a custom waveguide and has such a low resonate frequency). Dayton Audio drivers are commonly used in DIY projects and Peerless seems to be aimed at consumer OEM’s applications eg they mention Tv’s/sound bars in their product guide and someone tore down a 2015 Denon soundbar which used Peerless drivers.
As you may appreciate, the bass player will never understand as those are not bass frequencies ;>