The phon unit measures perceived loudness, not physical sound level

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)

In a common implementation of the loudness balancing procedure, we measure the level of a sound of interest (the test stimulus here) that matches the level of a 1000-Hz stimulus (the reference stimulus). For these studies, a 1000-Hz tone is always the reference sound, and it is presented at some fixed stimulus level (e.g., 40 dB SPL). The two sounds (the 1000-Hz reference and the test stimulus) are always presented in succession (never simultaneously) and sometimes to opposite ears if the listener has normal hearing. In a typical experiment, the method of adjustment is used where the listener adjusts the level of the test sound so that its loudness is equal to that of the reference sound. The level of the 1000-Hz tone in dB SPL is the loudness level of the test sound, measured in phons. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 745 (#expands, via linked claim)

Loudness level of a sound is the sound pressure level of a I-kHz tone in a plane wave and frontal incident that is as loud as the sound; its unit is “phon”. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1169 (#corroborates, via linked claim)

Categorization

• XREF: connects to: The phon unit anchors loudness to perceived equality across frequencies rather than raw SPL — Eric J. Heller, Why You Hear What You Hear- An…, 2002; Loudness is a subjective percept standardized against 1-kHz tone levels in phons; The phon scale defines loudness relative to equal-loudness matches at 1 kHz — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 745 (+6 more)

Related

• Loudness is a subjective percept standardized against 1-kHz tone levels in phons (similarity 0.95)
• The phon unit anchors loudness to perceived equality across frequencies rather than raw SPL (similarity 0.94)
• The phon scale defines loudness relative to equal-loudness matches at 1 kHz (similarity 0.92)
• Loudness is measured subjectively against 1 kHz reference tones (similarity 0.91)
• Loudness is measured by listeners assigning numbers relative to a reference sound. (similarity 0.89)
• The phon defines loudness level equal to dB SPL at 1 kHz (similarity 0.87)
• Perceived loudness does not map one-to-one onto acoustic amplitude (similarity 0.86)
• Loudness is perceptual and unmeasurable directly, while intensity is acoustic and directly quantifiable (similarity 0.86)
• Loudness, measured in sones, depends inherently on frequency content (similarity 0.86)
• Loudness depends on frequency, angle, duration, and envelope, not just level (similarity 0.85)
• Raising a sound’s loudness shifts its perceived pitch except near 1-2 kHz. (similarity 0.85)
• Loudness scales with frequency squared, requiring large amplitude at low frequencies (similarity 0.85)
• Loudness depends on more than physical sound intensity alone (similarity 0.84)
• Equal-loudness-contour weighting schemes failed as loudness meters (similarity 0.84)
• Loudness perception involves central mechanisms beyond cochlear vibration (similarity 0.84)

Broader Connections

• The phon scale defines loudness relative to equal-loudness matches at 1 kHz #expands (0.90) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 745
• Perceived loudness does not map one-to-one onto acoustic amplitude #corroborates (0.90) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 616
• Loudness is measured subjectively against 1 kHz reference tones #corroborates (0.85) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1169
• Perceived loudness and physical sound intensity follow different, non-intuitive mathematical scales #expands (0.85) — George Michelsen Foy, Zero Decibels, 53
• Loudness depends on more than physical sound intensity alone #corroborates (0.80) — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610
• Loudness depends on frequency, angle, duration, and envelope, not just level #expands (0.80) — Toole, Floyd E, Sound reproduction- the acoustics and…, 903
• Auditory cortex activation linearly reflects perceived loudness rather than physical intensity #corroborates (0.75) — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610