Loudness is a psychological percept measurable only through human report

Evidence

It is worth noting that loudness and intensity are two distinct concepts. Loudness is a psychological perception associated with sound, and is therefore a perceptual variable. We cannot measure it directly — we can only measure the loudness of a sound in the context of other sounds. Further, loudness measurements rely on human reports of loudness. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 675

Categorization

• DEFINE: Core conceptual definition — loudness is unmeasurable directly and requires human listeners, unlike physical intensity.