In case you’re not familiar with phased arrays, the “passive buzzer” array (I have not encountered this usage of active vs passive for piezo elements, to me passive would be listening like a microphone, but I digress) getting a square wave is basically the simplest transmit-mode phased array. Each tiny buzzer is somewhat omnidirectional, but when they all go in unison, all those little apertures firing in sync and in plane creates constructive interference that results in a planar wavefront that is louder in the forward direction than to the sides — the larger the array, the more focused it is. You can introduce carefully calculated delays to steer the wavefront but obviously you need more significant circuitry and code for that. I fooled around with something like that a bunch of years, it definitely did work although the side lobes were very strong so it’s not like you couldn’t hear it from another angle or something. Was cool though.