Overview
ISO 14257:2001 defines a standardized method for measuring and parametrically describing spatial sound distribution curves in workrooms to evaluate their acoustical performance. The standard specifies how to measure sound pressure level attenuation from a calibrated reference source as a function of distance (in octave bands), and how to extract two practical descriptors used for noise control: the rate of spatial decay per distance doubling and the excess sound pressure level relative to a free field. Measurements, data representation and reporting requirements are included, with normative annexes on source performance and correction methods.
Key topics and technical requirements
- Measurement method: Spatial sound distribution curves are measured in octave bands along prescribed paths and microphone positions using calibrated instrumentation.
- Reference sound source: Requirements and calibration/verification procedures are specified (see normative Annex A), referencing ISO 6926 for sound source calibration.
- Data representation: Sound distribution values D(r) are calculated from measured sound pressure levels and the source sound power; curves are plotted with a logarithmic distance axis.
- Parametric descriptors:
- Rate of spatial decay (DL) - slope in dB per distance doubling for defined distance ranges (near, middle, far).
- Excess of sound pressure level (DLf) - average difference between the room curve and a free-field reference (6 dB per doubling).
- Frequency-normalized curves: Guidance for producing a normalized spatial curve using A‑weighted pink noise when machine spectra are unknown.
- Corrections and limitations: Annex B addresses ground reflections and source directivity corrections; Annex C provides an example of use.
- Instrumentation and standards compliance: Measurement equipment and filters should comply with IEC/ISO instrument standards (e.g., IEC 61260 for filters).
Practical applications
ISO 14257 is intended for practical noise assessment and control in industrial and workroom environments. Typical uses:
- Acoustical qualification of rooms for noise control.
- Positioning machines and workstations to minimize worker exposure.
- Assessing need for additional sound absorption or acoustic treatments.
- Estimating screen (barrier) performance qualitatively before installation.
- Predicting noise immission when operating known machines at specified positions.
Who should use this standard
- Acoustical engineers and consultants
- Occupational hygienists and safety professionals
- Facility and production planners
- Equipment manufacturers evaluating room noise impact
- Researchers and test laboratories performing room acoustic characterization
Related standards
Normative references include ISO 6926, ISO 3741/3744/3745 (sound power methods), ISO 11690-1 (workplace acoustics guidance) and IEC/ISO standards for sound level meters and filters (IEC 60651, 60804, 61260). These provide complementary procedures for source calibration, instrumentation and broader workplace noise evaluation.