The Pico 4 internal speakers are not that terrible, but they sound much better with some ear muffs.
This adapter was printed in PCTG, and the ear muff itself in TPU (although a stiff filament would probably be fine too). The adapter pinches the muff, allowing it to be moved in 4 directions, but for bigger ears a larger ear muff or longer adapter might be needed!
The adapter itself can move back and forth along the strap.
The author marked this model as their own original creation.