DIN EN ISO 266:1997-08

The document specifies a series of preferred frequencies in order to provide a common basis for comparing the results of acoustical measurements. The frequency series is referred to the reference frequency of 1000 Hz, which is also the reference frequency to the definition of the phon (see ISO 31-7). The specification of the preferred frequency series reduces to a minimum the number of frequencie at which acoustical data need to be tabulated. Also measurement equipment may be specifically constructed for these frequencies.