Editing Particle velocity (section)

==Particle velocity level==
{{Other uses|Sound level (disambiguation){{!}}Sound level}}

'''Sound velocity level''' (SVL) or '''acoustic velocity level''' or '''particle velocity level''' is a [[Level (logarithmic quantity)|logarithmic measure]] of the effective particle velocity of a sound relative to a reference value.<br>
Sound velocity level, denoted ''L''<sub>''v''</sub> and measured in [[Decibel|dB]], is defined by<ref name=IEC60027-3>[http://webstore.iec.ch/webstore/webstore.nsf/artnum/028981 "Letter symbols to be used in electrical technology – Part 3: Logarithmic and related quantities, and their units"], ''IEC 60027-3 Ed. 3.0'', International Electrotechnical Commission, 19 July 2002.</ref>
:<math>L_v = \ln\!\left(\frac{v}{v_0}\right)\!~\mathrm{Np} = 2 \log_{10}\!\left(\frac{v}{v_0}\right)\!~\mathrm{B} = 20 \log_{10}\!\left(\frac{v}{v_0}\right)\!~\mathrm{dB},</math>
where
*''v'' is the [[root mean square]] particle velocity;
*''v''<sub>0</sub> is the ''reference particle velocity'';
*{{no break|1=1 Np = 1}} is the [[neper]];
*{{no break|1=1 B = {{sfrac|1|2}} ln 10}} is the [[Decibel|bel]];
*{{no break|1=1 dB = {{sfrac|1|20}} ln 10}} is the [[decibel]].

The commonly used reference particle velocity in air is<ref>Ross Roeser, Michael Valente, ''Audiology: Diagnosis'' (Thieme 2007), p. 240.</ref>
:<math>v_0 = 5 \times 10^{-8}~\mathrm{m/s}.</math>
The proper notations for sound velocity level using this reference are {{nobreak|''L''<sub>''v''/(5 × 10<sup>−8</sup> m/s)</sub>}} or {{nobreak|''L''<sub>''v''</sub> (re 5 × 10<sup>−8</sup> m/s)}}, but the notations {{nobreak|dB SVL}}, {{nobreak|dB(SVL)}}, dBSVL, or dB<sub>SVL</sub> are very common, even though they are not accepted by the SI.<ref name=NIST2008>Thompson, A. and Taylor, B. N. sec 8.7, "Logarithmic quantities and units: level, neper, bel", ''Guide for the Use of the International System of Units (SI) 2008 Edition'', NIST Special Publication 811, 2nd printing (November 2008), SP811 [http://physics.nist.gov/cuu/pdf/sp811.pdf PDF]</ref>