Overview
EN ISO 11820:1996 - "Acoustics - Measurements on silencers in situ" (CEN adoption of ISO 11820:1996) specifies methods for measuring the acoustic performance of silencers installed in their real operating environments. The standard covers both insertion loss and transmission loss measurements depending on the chosen method, and includes procedures for dealing with flow, background noise and field-specific corrections. It is intended for practical applications such as acceptance testing, acoustic analysis and refurbishment assessment of silencers used on HVAC systems, gas turbines, exhaust stacks, compressors, engines and similar plant.
Key Topics
- Scope & applicability: Passive and active silencers, baffles, louvres and other in-line acoustic attenuation devices. Not intended for closed high‑pressure systems where structure-borne sound dominates.
- Quantities measured: Sound pressure levels (octave and one‑third‑octave bands), sound power levels, static/total pressure differences, flow velocity and temperature at selected positions.
- Performance metrics: Definitions and calculation methods for insertion loss (D_is) and transmission loss (D_ts), including how to interpret results in situ versus laboratory (ISO 7235) data.
- Measurement procedures: Guidance on installation conditions, acoustic instrumentation, and flow/pressure/temperature measurement methods; calibration and use of directional microphones and turbulence windscreens (see annexes).
- Corrections & evaluation: Field corrections for non‑ideal sound fields (Annex A), background noise correction, evaluation of sound and flow measurements, and reporting requirements (what to record and include in test reports).
- Frequency ranges: Typical octave-band coverage from 63 Hz to 4 kHz (with options to extend to lower or higher bands or use one‑third‑octave bands where required).
Applications
- Acceptance testing of silencers after installation on industrial plant or ventilation systems.
- In-situ acoustic analysis to verify performance under real operating flow, pressure and temperature conditions.
- Design validation and troubleshooting for HVAC, power generation, exhaust/intake systems, and industrial noise control projects.
- Refurbishment and maintenance checks to quantify changes in silencer attenuation after cleaning or repair.
Who uses it: acoustic consultants, test laboratories, plant engineers, HVAC designers, procurement and compliance teams responsible for noise control.
Related Standards (if applicable)
- ISO 7235 - Laboratory measurements on ducted silencers (comparison point)
- ISO 3744 - Sound power determination (engineering method)
- ISO 5221 - Air flow measurement in ducts
- IEC 651, IEC 804 - Sound level meters and integrating meters (measurement instruments)
- Other annexes in EN ISO 11820 cover field corrections and microphone calibration.
Using EN ISO 11820 helps ensure repeatable, traceable in situ silencer measurements and provides the technical basis for meaningful comparison, acceptance criteria and noise‑control decisions in operational environments.