The SI unit of sound energy density is the pascal (Pa), which is 1 kg⋅m−1⋅s−2 in SI base units or 1 joule per cubic metre (J/m3).
[1]: Section 2.3.4: Derived units, Table 4 Sound energy density, denoted w, is defined by where The terms instantaneous energy density, maximum energy density, and peak energy density have meanings analogous to the related terms used for sound pressure.
The sound energy density level gives the ratio of a sound incidence as a sound energy value in comparison to the reference level of 1 pPa (= 10−12 pascals).
[2] It is a logarithmic measure of the ratio of two sound energy densities.
[1]: Chapter 4: Non-SI units that are accepted for use with the SI, Table 8 The sound energy density level, L(E), for a given sound energy density, E1, in pascals, is where E0 is the standard reference sound energy density[3]