olemus
heliaistingu subjektiivne mõõt, mis sõltub
- helirõhu tasemest, dB
- helisagedusst, Hz
- komponenthelide ajasuhetest

Wiktionary:
1. the perceptual strength or amplitude of sound pressure, measured in sones or phons
2. the physical strength of the sound pressure level, measured in decibels

ISO/TS 9241:
perception of a sound’s intensity

ISO 532:
perceived magnitude of a sound, which depends on the acoustic properties of the sound and the specific listening conditions, as estimated by otologically normal persons
Note 1. Loudness is expressed in sones.
Note 2. Loudness depends primarily upon the sound pressure level, although it also depends upon the frequency, waveform, bandwidth, and duration of the sound.
Note 3. One sone is the loudness of a sound with a loudness level of 40 phon.
Note 4. A sound that is twice as loud as another sound is characterized by doubling the number of sones.

mõõtühikud
(i) foon (phon)
1000 Hz puhtal etalontoonil põhinev logaritmiline suhteühik
https://en.wikipedia.org/wiki/Phon

(ii) soon (sone)
ISO 15006:
frontaalse 1000 Hz puhta tooni valjus helirõhu tasemel 40 dB, re 20 µPa
= subjective unit of loudness, as perceived by a person with normal hearing, equal to the loudness of a 1 000 Hz pure tone presented frontally with a sound pressure level of 40 dB, re 20 µPa

ülevaateid
https://en.wikipedia.org/wiki/Loudness

http://www.sengpielaudio.com/calculatorSonephon.htm

http://astro.pas.rochester.edu/~aquillen/phy103/Lectures/G_Loudness.pdf

https://www.itu.int/dms_pub/itu-r/opb/rep/r-rep-bs.2054-2-2011-pdf-e.pdf

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.301.8924&rep=rep1&type=pdf

https://courses.physics.illinois.edu/phys406/sp2017/Lecture_Notes/P406POM_Lecture_Notes/P406POM_Lect5.pdf