I recently devote myself to poor audio.
I recognized that the most important thing of the audio hobby is technology.
Important information is found everywhere around usual life.
UP4D technology was found from poor audio trial.
Limited materials like rough woods limited enclosure design, driver layout, size and so on.
It made me realized the advantage of unparallel driver layout.
Now I am trying the next UP4D application.
I try UP4D cavity resonator system.
Previous one was pipe resonator.
Cavity resonator system is somewhat advantageous for size and shape compared with pipe resonator.
Now I will incorporate pipe resonator with cavity resonator.
I will see what it can.