The 1935 Beasley survey first established US normal-hearing thresholds

Evidence

Due to the necessity of normative measures, Willis Beasley carried out a large survey to establish the thresholds of healthy listeners as part of a U.S. Public Health Service general health survey in 1935 and 1936. Beasley’s study was designed to obtain the audiometric thresholds for people who had good hearing (about 4,500 people), and people with presumed or suspected hearing loss were specifically excluded from data analysis. Using the Western Electric 2-A audiometer, the survey provided the first large-scale estimates of normal hearing in the frequency range from 64 to 8192 Hz reported in dB SPL (Glorig, 1966). — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 103

Categorization

• DEFINE: Defines the dB SPL vs dB HL distinction: physical reference vs perceptual reference, which underpins audiometer calibration.