Auditory physiologist Christopher Shera will discuss the science of sound before a showing of director Rob Reiner’s rockumentary “This Is Spinal Tap” at the Coolidge Corner Theatre next week. The movie about the fictional British heavy metal band Spinal Tap, including the band’s celebrated amplifiers that “go to 11” instead of 10, will be shown March 18 at 7 p.m. as part of the nonprofit theater’s “Science on Screen” series. Shera studies how the ear amplifies, analyzes, and even produces sound. He is an associate professor at Harvard Medical School and holds a doctorate in physics and neurobiology from the California Institute of Technology. Before the film, Shera will discuss how sound differs from silence, how loud an explosion is, and how loud we can go. General admission tickets are $10 and can be purchased at the theater or online at www.coolidge.org .