Fletcher and Munson’s 1933 loudness data remain essentially accurate today.

Evidence

Modern measurements are now included in the international standard (ISO 226-2003), which report equal-loudness contours very similar to Fletcher and Munson’s data illustrated in Figure 4–5. Even today, these contours are commonly called “Fletcher-Munson” curves. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 753

Categorization

• XREF: The longevity of Fletcher-Munson curves echoes classic results in other perceptual sciences that survived later measurement improvements.