Transmission loss test

Transmission Loss Testing Service – Comprehensive Acoustic Performance Evaluation for Materials, Components and Building Systems

As an ISO/IEC 17025 accredited independent testing laboratory, we offer specialised transmission loss testing services to manufacturers, engineering contractors, and quality assurance teams across the automotive, aerospace, construction, marine, HVAC, and industrial equipment sectors. Transmission loss – the reduction in sound energy as it passes through a material, panel, partition, or assembly – is a fundamental acoustic performance parameter that quantifies the sound insulation effectiveness of a product. Accurate measurement of transmission loss is essential for meeting building code requirements (e.g., STC – Sound Transmission Class, Rw – Weighted Sound Reduction Index), automotive NVH (Noise, Vibration, Harshness) targets, aerospace cabin noise regulations, and industrial noise control specifications. Our test protocols measure sound transmission loss across a wide frequency range (typically 50 Hz to 10 kHz) using standardised reverberation chamber and impedance tube methods, providing you with the data needed to optimise acoustic performance and ensure regulatory compliance. All methods are aligned with ISO, ASTM, and EN standards, including ISO 10140 (Acoustics – Laboratory measurement of sound insulation of building elements), ASTM E90 (Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions), ASTM E2611 (Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method), ISO 10534-2 (Impedance tube method), and EN ISO 10140 (European standard for sound insulation testing). Our inspection and test reports are recognised by national regulatory authorities, building code officials, and international certification bodies for product registration, type approval, and quality assurance.

Materials, Components and Systems We Regularly Test

Our acoustic test facilities accommodate a wide range of materials, assemblies, and finished products. Typical test articles include:

Building partitions and wall assemblies – drywall, masonry, concrete, timber stud walls, metal stud walls, and double-leaf constructions
Doors and door assemblies – solid wood, hollow metal, glass, acoustic, and fire-rated doors with seals and hardware
Windows and glazing systems – single, double, and triple-glazed units, laminated glass, and window frames
Floor and ceiling assemblies – concrete slabs, timber joist floors, floating floors, and suspended ceiling systems
Automotive and aerospace components – dash panels, door modules, floor pan insulators, headliners, and bulkhead assemblies
Acoustic insulation materials – mineral wool, fibreglass, foam, composite barriers, and mass-loaded vinyl
Industrial enclosures and equipment housings – generator enclosures, compressor housings, pump covers, and HVAC silencers
Composite panels and sandwich structures – honeycomb cores, foam cores, and laminated composites for transportation and marine applications
Seals, gaskets and edge treatments – for assessing the effect of perimeter sealing on overall transmission loss
Prototype and custom assemblies – for R&D and new product development

Test Methods – Laboratory Measurement of Airborne Sound Transmission Loss

Reverberation chamber method – ISO 10140 / ASTM E90 / EN ISO 10140 – We mount the test specimen (typically a building element or panel) in a test aperture separating two reverberation rooms: a source room (where the sound is generated) and a receiving room (where the transmitted sound is measured). A calibrated sound source generates pink noise or discrete tones in the source room, and microphones positioned in both rooms measure the spatially averaged sound pressure levels. The transmission loss (TL) is calculated from the difference in sound levels, the area of the test specimen, and the absorption of the receiving room. Measurements are performed at one‑third‑octave band frequencies from 50 Hz to 5 kHz (or up to 10 kHz for advanced testing). The results are used to determine the Sound Transmission Class (STC) or the Weighted Sound Reduction Index (Rw). The test is performed on a minimum of two specimens, and the average TL, the standard deviation, and the STC/Rw are reported.
Impedance tube (two‑microphone) method – ISO 10534-2 / ASTM E2611 – for normal incidence sound transmission loss – For small‑scale samples and for material characterisation, we use an impedance tube with two microphone positions to measure the normal incidence transmission loss. The specimen is placed in the tube, and broadband noise is generated at one end. The transfer function between the two microphones is measured, and the transmission loss is calculated using the transfer matrix method. This method is particularly suited for acoustic insulation materials, foam, and composite samples, and for R&D screening of materials. The measurement frequency range depends on the tube diameter – typically 50‑6 400 Hz for 100 mm diameter tubes, and up to 10 kHz for 29 mm diameter tubes.
Sound transmission class (STC) and weighted sound reduction index (Rw) calculation – ASTM E413 / ISO 717-1 – From the measured one‑third‑octave band transmission loss data, we calculate the STC (using ASTM E413) and the Rw (using ISO 717-1). These single‑number ratings provide a convenient measure of the overall sound insulation performance of the partition or component. The STC is widely used in North America, while Rw is used in Europe and internationally. The spectrum adaptation terms (Ctr for traffic noise, C for general indoor noise) are also reported for Rw to account for different noise spectra. A higher STC or Rw indicates better sound insulation; for example, a typical residential wall has an STC of 40‑50, while a high‑performance acoustic wall may have an STC of 60‑70.
Field transmission loss testing – ASTM E336 / ISO 16283-1 – for in‑situ measurement – For existing buildings and for assessing the sound insulation of completed constructions, we perform field transmission loss testing. The measurement procedure is similar to the laboratory method, but the test is conducted on the actual construction (e.g., an existing wall or floor) in the building. The field test provides the Field Sound Transmission Class (FSTC) or the apparent sound reduction index (R’w). The results are used for building commissioning, code compliance, and for diagnosing sound leakage paths.
Transmission loss at elevated temperatures – for high‑temperature insulation and exhaust systems – For components that operate at elevated temperatures (e.g., exhaust systems, engine enclosures), we perform transmission loss testing at specified temperatures (up to 200 °C or 400 °C) using a heated test cell. The test assesses the acoustic performance under thermal stress.
Flanking transmission assessment – for evaluating indirect sound transmission paths – For building elements, we use the reverberation room method with flanking paths (e.g., through adjacent structures, shared plenums) to assess the contribution of flanking transmission to the overall sound insulation. The flanking transmission loss is measured and reported separately, enabling you to design effective sound insulation strategies.

Test Specimen Preparation and Mounting – Ensuring Representative Results

Specimen dimensions – standardised for reverberation room testing – For the reverberation chamber method, the test specimen must be large enough to cover the test aperture (typically 2.5 m × 3.0 m for walls, or 1.2 m × 1.2 m for small panels). The specimen is constructed or assembled to match the actual end‑use configuration (e.g., with the specified framing, sealing, and hardware). For impedance tube testing, the specimen is a circular disc of the specified diameter (typically 29 mm, 100 mm, or 200 mm), cut to the exact tube diameter.
Sealing and edge treatment – to prevent sound leakage – ASTM E90 / ISO 10140 – We seal the edges of the test specimen in the test aperture using acoustic caulk, foam tape, or other sealing materials to prevent sound leakage around the edges. The edge sealing is specified in the test report and is included in the measured transmission loss.
Conditioning – to achieve equilibrium moisture and temperature – ASTM E90 / ISO 10140 – Before testing, the specimens are conditioned at the specified temperature (typically 23 °C) and humidity (typically 50 % RH) for a minimum of 24 hours (or until stable). The conditioning ensures that the material properties are stable at the start of the test.
Mounting of glazing and door assemblies – with the specified hardware and seals – For windows and doors, we mount the specimen in the test aperture with the specified hardware (hinges, locks, handles) and the seals (weather stripping, gaskets) installed. The test is performed with the door in the closed position, and the transmission loss is measured with the door locked and unlocked to assess the effect of seal compression.
Number of specimens and test repeats – for statistical confidence – For laboratory testing, we test a minimum of two specimens per material or assembly configuration. The average transmission loss and the STC/Rw are reported. Any significant variation between specimens (> 2 dB STC) is investigated and reported.

Frequency‑Dependent Transmission Loss – Characterising the Acoustic Performance

One‑third‑octave band transmission loss (TL) – the primary output of the test – The transmission loss is measured at each one‑third‑octave band frequency from 50 Hz to 5 kHz (or 10 kHz). The TL curve shows the sound insulation performance of the material or assembly at different frequencies. A high TL at low frequencies indicates good bass insulation; a high TL at high frequencies indicates good treble insulation. The TL curve is used to identify the coincidence dip (the frequency where the panel resonates) and the mass‑law region.
Mass‑law region – the relationship between TL and the mass of the panel – For single‑leaf panels, the TL increases by 6 dB per doubling of mass (the mass‑law). We compare the measured TL with the theoretical mass‑law prediction to assess the effectiveness of the panel. A deviation from the mass‑law (e.g., a lower TL than predicted) indicates the presence of sound leakage, resonance, or flanking paths.
Coincidence dip – the frequency at which the panel resonance reduces the TL – For thin panels (e.g., drywall, glass), there is a coincidence dip at a specific frequency where the bending wave velocity matches the speed of sound in air. The TL at the coincidence dip is typically 5‑15 dB lower than the mass‑law prediction. We report the coincidence frequency (fc) and the minimum TL at the coincidence dip.
Low‑frequency performance – assessing the bass insulation – For building partitions, the low‑frequency TL (50‑250 Hz) is critical for isolating low‑frequency noise from HVAC systems, traffic, and music. We report the TL at 50 Hz, 63 Hz, 80 Hz, 100 Hz, 125 Hz, and 160 Hz, and we provide the low‑frequency adaptation term (Ctr) for Rw to account for the low‑frequency performance in traffic noise scenarios.

Environmental and Durability Testing – Simulating Service Conditions

Temperature‑conditioned transmission loss – for assessing acoustic performance at elevated or reduced temperatures – For components that are installed in extreme temperature environments, we perform transmission loss testing at elevated temperatures (e.g., 40 °C, 60 °C, 80 °C) or at reduced temperatures (e.g., -20 °C, -40 °C) using a temperature‑controlled chamber. The test assesses the effect of temperature on the sound insulation performance.
Humidity‑conditioned transmission loss – for assessing the effect of moisture on acoustic performance – We condition the specimens at a high humidity (e.g., 95 % RH, 40 °C) for 48‑168 hours, and then perform the transmission loss test. The test assesses the effect of moisture on the insulation material and the resulting change in transmission loss.
Transmission loss after ageing and durability testing – for assessing long‑term acoustic performance – We subject the specimen to accelerated ageing (e.g., heat ageing, UV ageing) and then perform the transmission loss test. The test assesses the effect of ageing on the acoustic performance, particularly for polymeric materials and sealants.
Transmission loss with rain and water spray – for assessing the effect of water ingress – For outdoor elements (e.g., windows, glazing), we perform the transmission loss test after exposing the specimen to a rain‑spray test (ASTM E331) to assess the effect of water ingress on the acoustic insulation.

Data Analysis and Interpretation – Quantifying Acoustic Performance

Transmission loss curve – the primary output of the test – We provide the TL curve (TL vs. frequency) for each test specimen, along with the average TL for multiple specimens. The TL curve is presented in tabular form and plotted graphically.
Sound Transmission Class (STC) – ASTM E413 – the single‑number rating for North American markets – The STC is calculated from the TL curve using the ASTM E413 standard. The STC is a single number that represents the overall sound insulation performance of the partition. A higher STC indicates better insulation. We report the STC and the associated TL curve.
Weighted Sound Reduction Index (Rw) – ISO 717-1 – the single‑number rating for European and international markets – The Rw is calculated from the TL curve using the ISO 717-1 standard. The Rw is reported with the spectrum adaptation terms C and Ctr. We provide both the Rw and the adaptation terms, which are used for regulatory compliance in Europe and for international projects.
Field Sound Transmission Class (FSTC) and apparent sound reduction index (R’w) – for field measurements – For field measurements, we report the FSTC (ASTM E413) and the apparent R’w (ISO 717-1). The field ratings are typically lower than the laboratory ratings due to flanking paths and installation effects.
Statistical summary – for repeatability and uncertainty – For multiple specimens, we report the mean TL, the standard deviation, and the confidence intervals for the STC/Rw. A standard deviation of < 2 dB STC is considered excellent for laboratory testing.

Regulatory Compliance and Product Certification – Supporting Building Codes and Industry Standards

Our transmission loss testing services are performed in accordance with the most widely used international and national standards. The most commonly requested include:

ISO 10140 – Acoustics – Laboratory measurement of sound insulation of building elements – the international standard for laboratory transmission loss testing
ASTM E90 – Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions – the North American standard for laboratory transmission loss testing
EN ISO 10140 – European standard for sound insulation testing – for European market access
ASTM E413 – Standard Classification for Rating Sound Insulation – for calculating STC
ISO 717-1 – Acoustics – Rating of sound insulation in buildings and of building elements – Part 1: Airborne sound insulation – for calculating Rw and the adaptation terms
ASTM E336 – Standard Test Method for Measurement of Airborne Sound Attenuation between Rooms in Buildings – for field transmission loss testing
ISO 16283-1 – Acoustics – Field measurement of sound insulation in buildings and of building elements – Part 1: Airborne sound insulation – for field measurement of airborne sound insulation
ASTM E2611 – Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method – for impedance tube transmission loss testing
ISO 10534-2 – Acoustics – Determination of sound absorption coefficient and impedance in impedance tubes – Part 2: Transfer‑function method – for impedance tube testing

Report Acceptance and Regulatory Recognition

All transmission loss tests are conducted under our ISO/IEC 17025 accreditation, using calibrated sound sources, microphones, and data acquisition systems, all traceable to national and international reference standards. Our final test reports include: a complete description of the test article (material, dimensions, construction details), the test method and conditions (temperature, humidity, conditioning), the measured TL data (tabulated and plotted), the calculated STC or Rw (with adaptation terms if applicable), a statistical summary (mean, standard deviation, confidence intervals), a description of any observed resonance or coincidence effects, and a clear pass/fail verdict against your specified acceptance criteria (e.g., STC ≥ 45, Rw ≥ 50). These reports are accepted by building code officials, regulatory authorities, and international certification bodies for product registration, type approval, and quality assurance. Bilingual (English/Chinese) versions are available to facilitate submissions to domestic and international authorities and to support your global market access.