Overview
EN ISO 3745:2012/A1:2017 (CEN) is an amendment to ISO 3745:2012 that updates precision laboratory methods for determining sound power levels and sound energy levels of noise sources from sound pressure measurements in anechoic and hemi‑anechoic rooms. The amendment aligns room‑qualification procedures with ISO 26101:2017, revises Annex A (qualification of test rooms), and clarifies practical measurement requirements for conformity with machine‑noise and related EU directives.
Key topics and requirements
- Scope: Precision methods for measurements in anechoic and hemi‑anechoic rooms (laboratory conditions).
- Normative reference added: ISO 26101:2017 (qualification of free‑field environments).
- Room qualification (Annex A replacement) follows ISO 26101 procedures and includes:
- Default use of discrete‑frequency (e.g., pure tone or narrowband) qualification unless source is known to be broadband.
- Maximum allowable deviations from the inverse square law (measured vs. theoretical):
- Anechoic rooms: ≤ 630 Hz: ±1.5 dB; 800–5 000 Hz: ±1.0 dB; ≥ 6 300 Hz: ±1.5 dB
- Hemi‑anechoic rooms: ≤ 630 Hz: ±2.5 dB; 800–5 000 Hz: ±2.0 dB; ≥ 6 300 Hz: ±3.0 dB
- Frequency range to be qualified: at least 100 Hz to 10 000 Hz (rules for band selection and evaluation specified).
- Mathematical origin for inverse square evaluation must lie within the physical volume of the test source.
- Requirements for microphone traverse paths and spatial resolution updated (see ISO 26101).
- Reflecting plane in hemi‑anechoic rooms: sound absorption coefficient ≤ 0.06 over the qualified range.
- Qualification checks recommended after absorber modification and periodically (≤ 5 years).
- Annex B provides an alternative, source‑specific qualification method (not for general room qualification).
- Notes on relaxed background noise and test source stability limits consistent with ISO 26101.
Applications and users
This standard is used by:
- Acoustic test laboratories certifying anechoic/hemi‑anechoic rooms
- Manufacturers of machinery, appliances and components performing sound power/energy measurements
- Product compliance engineers demonstrating conformity with Directive 2006/42/EC (machinery)
- Acoustic consultants, R&D teams, and quality assurance groups conducting precision noise testing
Practical uses include sound power certification, R&D acoustic characterization, product noise labeling, and regulatory conformity testing.
Related standards
- ISO 3745:2012 (base document)
- ISO 26101:2017 (qualification of free‑field environments) - now a normative reference incorporated by this amendment
Keywords: EN ISO 3745:2012/A1:2017, ISO 3745 amendment, anechoic room qualification, hemi‑anechoic, sound power level, sound energy level, sound pressure measurement, ISO 26101.
