Synchronized Audio Convergence

Start with two audio amplifiers, each with its own speaker -- a computer is programmed to control this special sound system. Place one speaker 150 ft. in front of you, the other 150 ft. behind. One amplifier plays the word “Half”, the other the word “Bakery”. The sounds take a moment to travel. The amps are synchronized so that you hear the word “Halfbakery” where you're standing. Now try this experiment with two additional amps & speakers, placed to your left and right. Each speaker plays only one syllable of “Half-Ba-ke-ry”. The sounds will form the word at your position.

Move or add speakers, farther or closer, play longer messages, and program the synchronizer to adjust. Now have the system chop the sounds into even smaller bits. The various short bursts from the speakers won’t make sense unless you’re standing at the point of convergence, where you’ll hear the complete audio. Scramble the speaker patterns, use odd electronic signal phasing, add a “pink noise” hiss – make it even more alien to bystanders, and still crystal clear to the target listener. It might be possible to encode your message into an otherwise ordinary song!

Since this is a “private message” of sorts, maybe it’s at a certain tile in a public place where you’d stand to hear affirmations, your fortune, etc.