De institutione musica I.14: Quis modus sit audiendi.
Let us now discuss the manner of hearing. For something of this kind is accustomed to happen in sounds as when a stone thrown from afar sinks into marshes or still waters.
For first it gathers the wave into a very small circle, then spreads the rounds of waves in larger circles, until the motion, wearied, rests from stirring up the waves. And always the later and larger ripple is spread by a weaker impulse. But if there is anything that can hinder the growing waves, that motion immediately returns and, as if to the centre from which it had set out, is rounded again in the same ripples. So, when the struck air has made a sound, it drives another, nearer air, and stirs in a way a round wave of air, and so it is spread and is heard by all standing around at once. And the voice is fainter for him who stands farther off, since a weaker wave of the struck air reaches him.