Helmholtz resonators are the basis of mechanical acoustics...
As you know i used them in my first room a lot ...
Distribution and location matter ...
Now in my second room with smaller speakers , i designed a new porthole for them using different straws tuned for this goal exactly as when we compute the right size of the neck volume and diameter of the resonator body ...
Then you understand my perspective ...
My goal was first learning acoustics then improve my sound without cost ...
Thanks for the information...
My best to you ...
In the late 70’s Randy Hooker aka RH Labs. Made a subwoofer that was a helmholtz resonator. It was a passive subwoofer down firing into a slot. It was huge in comparison to modern subwoofers, about 3 feet by 2 feet by 2 feet. They made beautiful if somewhat colored bass. Inside the enclosure the driver was housed in a larger compartment which was slot loaded into a smaller compartment. It resonated at 20 Hz forcing the driver to go down low. It was a pleated 12" paper driver, nothing special. There were no subwoofer drivers back then.