Audio beamforming is a thing.

What he did doesn’t sound like it’s capable of achieving that. Unless he tried to make a bunch of separate chambers for standing waves for different frequencies or something, you can’t do much with a single source (and we’re talking at least some dozen resonance chambers). Beamforming is usually done with phased arrays of ultrasonic transducers, and measurement of how audio echoes in the room.

Might have been trying to make directional speakers, otherwise (transducer arrays are often used to make that!). But that’s ALSO not doable with such a small change, you need a bunch of bullshit like at least a cone, or once again by using more sources.

Could also simply put up some lazy ass half domes behind the speaker and behind where he would be sitting, but that’s ALSO not what he did