Measurement of Loudness, Part I: Methods, Problems, and Pitfalls

It is a matter of everyday experience that sounds vary in their perceived strength, from the barely perceptible whisper coming from across the room to the overwhelming roar of a jet engine coming from the end of an airport runway. Loudness is a salient feature of auditory experience, closely associated with measures of acoustical level (energy, power, or pressure) but not identical to any of them. It is a relatively straightforward matter for a person to note whether one sound is louder or softer than another, or to rank order a set of sounds with regard to their loudness. To measure loudness, however, in the typical sense of “measuring,” requires more than just ranking the experiences from softest to loudest. It entails quantifying how much louder (e.g., determining whether the ratio or difference in the loudness of sounds A and B is greater or smaller than the ratio or difference in loudness of sounds C and D).