A rudimentary internet search for “equal loudness curve” results in page after page of articles and posts on Fletcher-Munson (FM) curves. While some articles mention that the 1933 findings have been replaced a couple of times over, most do not. How can 90-year-old findings based on a small set of participant data that has been challenged and replaced still dominate the majority of conversations on equal loudness? What further improvements to the current standard is being called for by the published literature?
This literature review first outlines the historical timeline and published debate around equal-loudness-level research and standards in an effort to understand why FM curves still dominate popular discussion. Despite early contradictory findings, there was a decently long stretch between Fletcher & Munson’s findings and the next determination. With the new contours of the 1950’s paving the way toward ISO 226, there is a corresponding increase in articles critical of the newer findings.
Researchers begin to question the adequacy of equal-loudness-level contours as a representation of perceived loudness among the general population. Articles point at shortcomings in representative age , gender and listener location in several of the contours/standards. Additional published works also layout errors in ISO 226 methodology and conclusions . Challenges to sample size and make up, method and mathematical discrepancies are all found in published critiques.
It may remain undetermined whether the length of time FM curves dominated as the default data set or the increasing controversy over every new method and standard is the cause of the continued popular use of “Fletcher-Munson curves” instead of more current phraseology. What is clear is researchers are calling for and exploring more nuanced and inclusive understanding of how we perceive loudness.
