A pulse inverts when reflecting off a fixed string end

Evidence

Up to now, we have skirted an important issue: the string ends have been fixed, as is normally the case in musical instruments. Nonetheless, we should consider the possibility of free ends, arranged by connecting the end of the string to a small massless ring allowed to frictionlessly ride up and down a vertical post. Pulses behave differently when they meet a free versus a fixed end, in analogy to pressure pulses in the air columns arriving at closed and open ends of tubes. It is best to think of the string displacement as analogous to pressure: positive displacement (positive y) of the string corresponds to compression above the background atmospheric pressure, and negative displacement corresponds to rarefaction. Using this analogy, a string tied down at the end corresponds to an open tube, where the pressure is being held fixed at the background atmospheric pressure. Therefore, we expect a pulse arriving at a fixed end of the string to return inverted, just like the pressure pulses did at the open end of the tube. — Eric J. Heller, Why You Hear What You Hear- An…, 849

Categorization

• XREF: The fixed-end-reflection mechanism connects to how open/closed tube resonances shape wind instrument timbre.