scope:

For certain acoustical measurements, a constant-frequency increment is a suitable spacing. More commonly, however, a constant-percentage increment is adopted and the frequencies then form a geometric series. This standard deals with the geometric series.

The present standard is not concerned with specification of preferred frequencies for music or musical instruments, or with specification of exact frequencies for bandpass filters.

PURPOSE

Use of a variety of frequencies for acoustical measurements makes comparison of results inconvenient. Some of the difficulties arise from use of different intervals or different starting frequencies for a series. The purpose of this standard, therefore, is to refer all frequency series to a single reference frequency, to specify other preferred frequencies, and to specify frequency levels and band numbers in such a way as to afford a maximum number of frequencies common to the various series. The resulting simplification thus reduces, to a minimum, the number of frequencies at which acoustical data need to be tabulated. Equipment may be constructed specifically, instruments scales can be labelled, and graph paper can be printed in advance, for those particular frequencies.