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 different frequencies or something, you can't do much with a single source (and we're talking at least a few dozen resonance chambers, or else the sheer width of wavelength ranges makes this precision impossible). 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. Possibly he just modified the angle of the elements in the speaker to all aim at his head, which would actually be reasonable (yet not have much effect on quality, just volume), but it doesn't sound like that's what he did.

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