Like billiards, with acoustics, it's all about the angles
Sound waves reflect the same way billiard balls do: the angle of reflection equals the angle of incidence. This is also called a specular reflection.
At least that's how sound reflects when hitting a smooth surface.
When the surface is craggy, like if it has bumps, angles, ridges, pyramids, or convex curves, some of the sound diffuses, or scatters.
If a surface is small, like a person standing a few feet away from a wall, the small surface of the person would not reflect the sound waves. Instead, the waves would continue around the preson and reflect off the wall.
This is the 3rd in a series of 4 videos introducing the fundamental principles of acoustics. The videos are produced by Michael Ermann, a tenured professor at Virginia Tech’s School of Architecture + Design, and author of the book Architectural Acoustics Illustrated (Wiley, 2015), which “translates the field of acoustics into the graphic language of architecture.”
All four videos, along with many others on a variety of architectural and construction-related subject matter, are available at Amber-book.com, a website that provides study materials for students preparing to take the ARE (Architectural Registration Exam), the professional licensure examination adopted by the United States.