This Part 2 of EN 50332 specifies matching values for the use of battery-operated audio equipment and headphones/earphones defined for the use with those and with standardised connectors allowing to combine components of different manufacturers or different design sold separately in order to avoid possible hearing impairment by excessive sound pressure resulting from them.
Compared with "one-package sets" the sound pressure level at the ear cannot be fixed by only one condition but needs at least two characteristics, one each for player and the headphones/earphones, defined by the matching values for their connection.