View source for Phon

{{short description|Logarithmic unit of loudness level}}
{{other uses}}
[[File:Lindos1.svg|thumb|upright=1.3|right|Equal-loudness contours]]
The '''phon''' is a logarithmic [[physical unit|unit]] of [[loudness]] level for tones and complex sounds. Loudness is measured in [[sone]]s, a linear unit. Human sensitivity to [[sound]] is variable across different [[frequencies]], so although two different tones may present an identical [[sound pressure]] to a human ear, they may be [[psychoacoustics|psychoacoustically]] perceived as differing in loudness. The purpose of the phon is to provide a logarithmic measurement (like [[decibels]]) for perceived sound magnitude, while the primary loudness standard methods result in a linear representation. A sound with a loudness of 1&nbsp;sone is judged equally loud as a 1&nbsp;kHz tone with a sound pressure level of 40&nbsp;decibels above 20&nbsp;micropascals.<ref>William M. Hartmann, ''Signals, Sound, and Sensation'', American Institute of Physics, 2004. {{ISBN|1-56396-283-7}}.</ref> The phon is psychophysically matched to a reference frequency of 1&nbsp;kHz.<ref>
{{Cite web
 |url=http://www.animations.physics.unsw.edu.au/jw/dB.htm#Loudness
 |title=dB: What is a decibel?
 |website=www.animations.physics.unsw.edu.au
 |access-date=2019-01-12
}}</ref> In other words, the phon matches the sound pressure level ([[dB SPL|SPL]]) in decibels of a similarly perceived 1{{nbsp}}kHz pure tone.<ref>
{{Cite journal
 |date=1974-07-01
 |title=Combining the sone and phon scales
 |last1=Pease |first1=C.B.
 |journal=Applied Acoustics
 |language=en
 |volume=7 |issue=3 |pages=167–181 
 |doi=10.1016/0003-682X(74)90011-5
 |issn=0003-682X
}}</ref> For instance, if a sound is perceived to be equal in intensity to a 1{{nbsp}}kHz tone with an SPL of 50{{nnbsp}}dB, then it has a loudness of 50{{nbsp}}phons, regardless of its physical properties.<ref>
{{Cite web
 |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/phon.html|title=Loudness Units: Phons and Sones
 |website=hyperphysics.phy-astr.gsu.edu
 |access-date=2019-01-12
}}</ref> The phon was proposed in DIN&nbsp;45631 and ISO&nbsp;532&nbsp;B by [[Stanley Smith Stevens]].<ref>[http://www.phys.unsw.edu.au/~jw/dB.html#log UNSW Music Acoustics<!-- Bot generated title -->].</ref>{{not in source|date=May 2024}}

==Definition==

By definition, the loudness level in phons of a sound is the sound pressure level (in [[dB&nbsp;SPL]]) of a 1&nbsp;kHz [[pure tone]] that is judged as having the same [[loudness]].<ref>{{cite web |title=phon |url=https://asastandards.org/Terms/phon/ |website=Welcome to ASA Standards |publisher=Acoustical Society of America |access-date=14 December 2020}}</ref>{{Clarify|date=July 2018}}{{Examples|date=July 2018}} The phon unit is not an [[SI unit]] in metrology. It is defined as a unit of loudness level by the [[American National Standards Institute]] in the ''Acoustical Terminology'' standard [[ANSI/ASA S1.1-2013]]. Because the phon is a unit associated with a subjective percept, it is obtained by presenting the considered sound to a group of normal-hearing human listeners and by taking the median of the loudness levels they report.

Such measurements have been performed for known sounds, such as pure tones at different frequencies and levels. The [[equal-loudness contour]]s are a way of mapping the dB&nbsp;SPL of a pure tone to the perceived loudness level in phons (see [[loudness]] for details).

==See also==
*[[A-weighting]]

==References==
{{reflist}}

==Further reading==
* {{cite book |title=Logarithmen, Normzahlen, Dezibel, Neper, Phon - natürlich verwandt! |language=German |trans-title=Logarithms, preferred numbers, decibel, neper, phon - naturally related! |author-first=Eugen |author-last=Paulin |date=2007-09-01 |url=http://www.rechenschieber.org/Normzahlen.pdf |url-status=live |archive-url=https://web.archive.org/web/20161218223050/http://www.rechenschieber.org/Normzahlen.pdf |archive-date=2016-12-18}}

==External links==
*[https://web.archive.org/web/20051028103357/http://ccrma.stanford.edu/~jos/TimeFreqDisplay/Sones_Phons.html Explanation with definitions] 
*[http://www.sengpielaudio.com/calculatorSonephon.htm Correlation between sones und phons − calculator]

[[Category:Hearing]]
[[Category:Human-based units of measurement]] 
[[Category:Units of sound]]
[[Category:Acoustics]]
[[Category:Sound]]