Encyclopedia
Spectral density
Limit as the bandwidth of frequencies approaches zero of the root mean square value of a quantity in the sound field divided by the bandwidth. The type of quantity (sound pressure, vibrational velocity, etc.) must be specified [IEC 50 (801)]
Source: "State System for Ensuring Uniformity of Measurements. Hydroacoustic Measurements. Terms and Definitions. GOST R 50.2.037-2004"
(approved by the Decree of Gosstandart Russia dated February 11, 2004 No. 55-st)