Sound attenuation testing standards define the laboratory and field procedures used to measure how effectively building elements, acoustic materials, and noise control devices reduce sound transmission. This guide summarizes the key ISO, IEC, ASTM, EN, and GB standards, the measurable acoustic parameters, typical sample requirements, and the testing methodologies applied by accredited third-party laboratories when evaluating sound attenuation performance.
Technical Overview
Sound attenuation testing, often referred to as sound insulation or sound transmission loss testing, quantifies the ability of a material, component, or structure to reduce the acoustic energy passing through it. The evaluation is performed across a defined frequency range, typically in one-third-octave bands from 100 Hz to 3150 Hz (extended ranges of 50 Hz to 5000 Hz are increasingly used for low-frequency accuracy). Results are expressed as single-number ratings that allow direct comparison between products and verification against regulatory or contractual requirements.
The principal international framework is defined by ISO and ASTM, with European (EN) and Chinese national (GB) standards largely harmonized with these documents. Key reference standards include ISO 10140 (laboratory measurement of sound insulation of building elements), ISO 16283 (field measurement of sound insulation in buildings), ISO 717 (rating of sound insulation), ASTM E90 (laboratory measurement of airborne sound transmission loss), and ASTM E413 (classification for rating sound insulation). Instrumentation requirements are governed by IEC 61672 for sound level meters and IEC 60942 for acoustic calibrators.
Testing Samples
Building Elements and Partitions
Full-scale wall assemblies, floor and ceiling systems, doors, windows, glazing units, curtain wall sections, and operable partitions are tested in laboratory transmission suites. Specimen dimensions are prescribed by the governing standard, typically requiring an effective test opening of approximately 10 square meters for walls and 10 to 20 square meters for floors, constructed to match the intended field installation including joints, sealants, and mounting conditions.
Acoustic Materials and Panels
Porous absorbers, resonant panels, mineral wool, acoustic foams, composites, and barrier mats are evaluated for sound absorption coefficient and transmission loss. Small circular or rectangular specimens are used for impedance tube testing, while larger panels of up to 10 to 12 square meters are required for reverberation room methods.
HVAC Components and Silencers
Ducted silencers, lined duct sections, flexible ducts, and terminal units are tested to determine dynamic insertion loss, self-generated noise (flow noise), and pressure drop as functions of airflow velocity, in accordance with ISO 7235 and ASTM E477.
Hearing Protection and Personal Devices
Earmuffs, earplugs, and communication headsets are assessed for real-ear attenuation using human test subjects under ISO 4869-1, from which single-number ratings such as SNR, HML, and NRR values are derived.
Testing Items
Depending on the product type and applicable standard, the following parameters are commonly measured and reported:
- Airborne sound transmission loss (TL) and sound reduction index (R) in one-third-octave bands
- Weighted sound reduction index Rw with spectrum adaptation terms C and Ctr (ISO 717-1)
- Sound Transmission Class, STC (ASTM E413), and Outdoor-Indoor Transmission Class, OITC (ASTM E1332)
- Normalized and standardized impact sound pressure level, Ln and Ln,w (ISO 717-2), and Impact Insulation Class, IIC (ASTM E989)
- Apparent sound reduction index R' and standardized level difference DnT for field evaluations (ISO 16283)
- Weighted sound absorption coefficient w and Noise Reduction Coefficient, NRC (ISO 354, ASTM C423)
- Dynamic insertion loss and regenerated noise of duct silencers (ISO 7235, ASTM E477)
- Real-ear attenuation values and single-number protection ratings for hearing protectors (ISO 4869)
Testing Methods
Laboratory Airborne Sound Insulation
The reference method uses two adjacent reverberation rooms separated by a test opening in which the specimen is mounted. Broadband noise is generated in the source room, and spatially averaged sound pressure levels are measured in both rooms using rotating microphone booms or fixed microphone arrays. Reverberation time in the receiving room is measured to account for absorption, and the sound reduction index is calculated from the level difference and the receiving room correction. The procedure follows ISO 10140-2 or ASTM E90, with flanking transmission suppressed by structural isolation of the test frame.
Field Sound Insulation Measurement
For completed buildings, in-situ measurements are conducted per ISO 16283-1 (airborne, internal and façade), ISO 16283-2 (impact), and ISO 16283-3 (façade sound insulation), or their ASTM equivalents E336 and E1007. Because flanking paths and workmanship affect results, field values are reported as apparent sound reduction index or standardized level difference rather than intrinsic material properties.
Sound Absorption Measurement
- Impedance tube method (ISO 10534-2, ASTM E1050): the transfer function between two microphone positions in an impedance tube determines normal-incidence absorption for small material samples, suitable for R&D and quality control.
Impact Sound Insulation
A standardized tapping machine meeting ISO 10140-5 is operated on the floor specimen, and the sound pressure levels in the receiving room below are measured and normalized to a reference absorption, yielding Ln in frequency bands and the single-number Ln,w after ISO 717-2 or IIC after ASTM E989.
Single-Number Rating Determination
Measured third-octave band data are fitted against reference contours defined in ISO 717-1, ISO 717-2, ASTM E413, and ASTM E989 to produce the reported single-number ratings. Spectrum adaptation terms account for typical noise sources such as road traffic or music, which contain more low-frequency energy than the reference contour.
Instrumentation and Quality Assurance
All measurements employ Class 1 instrumentation compliant with IEC 61672 and calibrated with IEC 60942 acoustic calibrators before and after each test sequence. Laboratory facilities must demonstrate qualification per ISO 10140-5 and maintain accreditation to ISO/IEC 17025 for the reported scope of testing.
Applications
Sound attenuation test data support a wide range of engineering, regulatory, and commercial objectives:
- Compliance demonstration against building codes and acoustic design requirements, such as GB 50118 in China and national building regulations in Europe and North America
- Product certification, declaration of performance, and marking programs for doors, windows, glazing, and partition systems
- Green building and wellness certification schemes, where verified acoustic performance contributes to indoor environmental quality credits
- HVAC system design, including silencer selection based on measured insertion loss and self-noise data
- Industrial noise control and occupational hearing conservation programs relying on laboratory-rated protectors and engineered barriers
- Research and development of new acoustic materials, multilayer composites, and lightweight high-insulation assemblies
- Dispute resolution and post-construction verification of contractual acoustic performance on completed projects
FAQ
What is the difference between STC and Rw?
STC is defined by ASTM E413 and was originally based on speech-frequency speech privacy criteria, while Rw is the ISO 717-1 equivalent used internationally. Both are derived from third-octave band transmission loss data between 125 Hz and 4000 Hz using slightly different reference contours, so values are similar but not interchangeable.
Why are field results lower than laboratory results?
Laboratory facilities eliminate flanking transmission, whereas real buildings contain indirect paths through connected walls, floors, and façades, as well as workmanship variability. Field ratings such as R' and DnT therefore typically measure 3 to 8 dB lower than the corresponding laboratory value for the same element.
Which frequency range is covered by standard measurements?
Conventional laboratory measurements cover 100 Hz to 3150 Hz in one-third-octave bands. Extended-range measurements from 50 Hz to 5000 Hz are available and increasingly requested for lightweight constructions and low-frequency noise sources.
How large must a laboratory test specimen be?
ISO 10140 and ASTM E90 generally require a test opening of approximately 10 square meters for walls, with the width and height not differing by more than a factor of 2.5. Doors and windows are tested at their real opening size with a filler wall of documented insulation performance.
Can small material samples be tested instead of full assemblies?
Impedance tube testing per ISO 10534-2 or ASTM E1050 provides normal-incidence absorption and transmission loss on small specimens and is useful for screening, but recognized single-number ratings for building products require full-scale reverberation room or transmission suite testing.