Loudness is perceptual and unmeasurable directly, while intensity is acoustic and directly quantifiable

Evidence

Although the perceived loudness of an acoustic sound is related to its amplitude, there is not a simple one-to-one functional relationship. As a psychoacoustic effect, it is affected by both the context and nature of the sound. It is also difficult to measure because it is dependent on the interpretation by listeners of what they hear. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 616 (#corroborates, via linked claim)

Loudness is mainly the perceptual correlate of sound intensity, which is usually expressed in dB SPL as sound pressure level on a logarithmic scale. However, loudness judgments are also affected by several other variables, including physical sound parameters like e.g. duration, spectral content and temporal modulation as well many more acoustic and non-acoustic factors, including the particular task or context and personal factors like the individual hearing status (Florentine et al. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610 (#expands, via linked claim)

Categorization

• XREF: connects to: Loudness depends on more than physical sound intensity alone — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610; Loudness growth with intensity requires experimental quantification, not intuition; Perceived loudness and physical sound intensity follow different, non-intuitive mathematical scales — George Michelsen Foy, Zero Decibels: The Quest for Absolute…, 53 (+6 more)

Related

• Loudness depends on more than physical sound intensity alone (similarity 0.95)
• Loudness depends on frequency, angle, duration, and envelope, not just level (similarity 0.93)
• Perceived loudness does not map one-to-one onto acoustic amplitude (similarity 0.92)
• Loudness growth with intensity requires experimental quantification, not intuition (similarity 0.92)
• Loudness scales with frequency squared, requiring large amplitude at low frequencies (similarity 0.92)
• Sound intensity level and sound pressure level are roughly equivalent (similarity 0.91)
• Loudness, measured in sones, depends inherently on frequency content (similarity 0.91)
• Loudness perception is essentially logarithmic (similarity 0.90)
• Loudness is a psychological percept measurable only through human report (similarity 0.90)
• Loudness is perceptual while intensity is physical and must be distinguished (similarity 0.89)
• Loudness perception involves central mechanisms beyond cochlear vibration (similarity 0.89)
• Loudness is measured by listeners assigning numbers relative to a reference sound. (similarity 0.89)
• Loudness is the sensation most directly tied to sound intensity (similarity 0.89)
• Binaural loudness constancy is partly physical and partly cognitive in origin (similarity 0.88)
• Loudness as perception can never be directly measured physiologically (similarity 0.87)

Broader Connections

• Loudness depends on more than physical sound intensity alone #expands (0.90) — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610
• Perceived loudness does not map one-to-one onto acoustic amplitude #corroborates (0.90) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 616
• Perceived loudness and physical sound intensity follow different, non-intuitive mathematical scales #expands (0.85) — George Michelsen Foy, Zero Decibels, 53
• Loudness is a subjective percept standardized against 1-kHz tone levels in phons #expands (0.85)
• Loudness grows as a power law of physical intensity so relative changes match #expands (0.80) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1262
• Loudness is measured subjectively against 1 kHz reference tones #expands (0.80) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1169
• Loudness depends on frequency, angle, duration, and envelope, not just level #expands (0.80) — Toole, Floyd E, Sound reproduction- the acoustics and…, 903
• Loudness growth with intensity requires experimental quantification, not intuition #qualifies (0.75)
• Sound quality is fundamentally subjective and requires perceptual testing to characterize #expands (0.75)