Sound spreads three-dimensionally rather than traveling on a fixed beam

Evidence

So far we have only considered sound as a disturbance that propagates in one direction. However, in reality sound propagates in three dimensions. This means that the sound from a source does not travel on a constant beam; instead it spreads out as it travels away from the radiating source, as shown in Figure 1.10. — David Howard, Jamie Angus, coustics and Psychoacoustics, 280