Evaluation of loudness for noise assuming environmental noise conditions: A study based on Stevens' power law

In recent years, metrics for loudness that model the human auditory system in detail have been developed, and their application to environmental noise assessment is highly anticipated. For calculating loudness of stationary sounds, ISO 532 provides two methods: Part 1 (Zwicker method) and Part 2 (Moore–Glasberg method). Both methods estimate loudness from sound energy using formulas derived from Stevens' power law. However, differences in the definition of the power exponent are considered a key factor leading to discrepancies in loudness values for the identical sound stimulus. To understand the quantitative relationship between sound energy and loudness in the context of environmental noise, we conducted loudness evaluation experiments using the magnitude estimation (ME) method with three broadband noises simulating environmental noise and 1/1-octave band noises with center frequencies ranging from 63 to 1000 Hz. The exponent in Stevens' power law was derived and analyzed. Results showed that the exponent ranged from 0.17 to 0.25, and it tended to be larger for low-frequency or low-frequency-dominant noise.