Overview
ISO 7574-4:1985 is part of the ISO 7574 series on acoustics and provides statistical methods for determining and verifying stated noise emission values for batches (lots) of machinery and equipment. Published in 1985, Part 4 focuses on how a labeller should pick a labelled noise value and how a batch can be checked by sampling. The standard assumes noise emission values approximate a normal distribution and addresses one‑sided (upper‑limit) verification only. It does not cover remedial actions if a lot fails verification.
Key topics and technical requirements
- Labelled value guidance: Procedures and formulae to help a labeller determine a labelled noise emission value (Lc) for a family of machines, using measured sample means and a specified reference standard deviation (σM).
- Reference standard deviation: A required σM (reference standard deviation) for each family of machines. Guidance is included if the actual total standard deviation differs from σM.
- Sampling plans: Three equivalent sampling procedures are specified:
- Single sampling inspection
- Double sampling inspection
- Sequential sampling inspection
Each plan uses specified sample sizes, decision limits and acceptability constants (k, kd, k1 etc.) to decide whether a batch conforms to its labelled value.
- Operating characteristic (OC) curves: The standard provides OC curves and tables to evaluate producer’s and consumer’s risks and to relate sample size to acceptance probability.
- Decision rules: Clear accept/reject rules based on sample statistics (sample mean, sample variance) and tabulated constants. Typical design values used include a producer acceptance probability of 95% with about 6.5% of machines allowed to exceed the labelled value.
- Measurement conditions: Measurements must follow the specific measurement test code for the machine family and be performed under reproducibility conditions by qualified laboratories.
Practical applications and users
ISO 7574-4 is practical for:
- Manufacturers and labellers who need to publish or justify a labelled noise emission value for a production batch.
- Acoustic testing laboratories that perform batch verification by sampling.
- Quality managers and product compliance teams responsible for noise labelling programs and statistical quality control.
- Regulatory bodies and certification organizations that require statistically defensible batch verification procedures for machinery noise compliance.
Practical uses include factory acceptance testing, noise label verification, supplier quality checks and conformity assessment where sampling (not 100% testing) is needed.
Related standards
- ISO 7574-1 (General considerations and definitions)
- ISO 4871 (Acoustics - Noise labelling of machinery and equipment)
- ISO 3951 (Sampling procedures and charts for inspection by variables)
ISO 7574-4 remains a key reference when implementing statistical sampling for noise emission verification, providing formulas, tables and OC curves to balance producer and consumer risks in noise labelling and compliance programs.