How did shaping hands around the mouth function as a crude acoustic director?

It was designed to push sound waves forward rather than letting them scatter in all directions.

The technique of cupping hands around the mouth served as a basic acoustic director by physically manipulating the sound waves emanating from the speaker. Instead of allowing the energy from the voice to radiate outward in a disorganized spherical pattern where it would quickly dissipate and lose volume and clarity, the shape formed by the hands served to channel and direct the bulk of the acoustic energy forward, aiming it toward the intended listeners. This action provided a modest increase in projection and allowed the sound to travel a slightly greater distance before succumbing to the normal physics of sound propagation in open air. However, this required significant physical effort and consistency from the speaker.