Fabric sound insulation testing service

Fabric Sound Insulation Testing Service – Accredited ISO/IEC 17025 Acoustic Performance Assessment for the Croatian Market

Fabric sound insulation is a critical acoustic performance parameter for textiles, upholstery, curtains, wall coverings, automotive headliners, acoustic panels, and technical textiles used in buildings, vehicles, and industrial environments. The ability of a fabric to block, absorb, or attenuate airborne sound directly affects the acoustic comfort, privacy, noise control, and regulatory compliance of the end application. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo gospodarstva i održivog razvoja, the Državni inspektorat, and the Ministarstvo graditeljstva i prostornoga uređenja enforce strict quality, building, and environmental standards aligned with EU directives and HRN EN (Croatian standards based on European norms), the accurate evaluation of fabric sound insulation is essential for product certification, building acoustics compliance, supplier qualification, quality control in manufacturing, and import-export processes. Our laboratory offers a comprehensive fabric sound insulation testing service, applying standardized methods that measure sound transmission loss, sound absorption coefficient, and noise reduction performance across a wide frequency range, following the requirements of ISO 10534, ISO 354, ASTM E1050, and EN ISO 11654. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, product validation, and market access in Croatia and the European Union.

Fabric and Textile Samples We Regularly Test

Our laboratory receives a wide variety of fabrics and textile materials for sound insulation testing. Typical samples include:

• Upholstery fabrics and furniture textiles – for seating, wall panels, and acoustic partitions in commercial and residential buildings.
• Curtain and drapery fabrics – for acoustic curtains, stage drapes, and noise-reducing window coverings.
• Automotive and transportation textiles – headliners, door panels, floor coverings, and interior trim fabrics for cars, trains, and aircraft.
• Acoustic wall coverings and ceiling panels – for sound absorption and sound insulation in offices, theaters, and recording studios.
• Technical textiles and nonwovens – for industrial noise control, machinery enclosures, and acoustic barriers.
• Composite textile materials – with laminated layers, foam backing, or acoustic membranes.
• Prototype and new fabric designs – submitted by manufacturers for validation of acoustic performance before series production.
• Field-retrieved fabric samples – for failure analysis and remaining acoustic life assessment.

Sound Transmission Loss Testing – Evaluating the Airborne Sound Insulation of Fabrics

Sound transmission loss (STL) is a fundamental measure of the ability of a fabric or textile material to block airborne sound from passing through it. Our tests measure the reduction in sound power as it passes through the fabric sample, using standardized methods and specialized acoustic test fixtures. This parameter is critical for curtains, partitions, and fabric-based acoustic barriers.

• Sound transmission loss measurement for fabrics (ASTM E90 / ISO 15186 / HRN EN ISO 15186 – for test specimens) – the fabric sample is mounted in a test fixture between two acoustically isolated chambers (a source room and a receiving room, or using a smaller impedance tube fixture). A broadband sound source is used in the source chamber, and the sound pressure levels are measured in both chambers using calibrated microphones. The transmission loss (in dB) is calculated for each 1/3‑octave band frequency (from 100 Hz to 5000 Hz). We report the STL values, the weighted sound transmission loss (Rw) according to ISO 717-1, and the sound reduction index for the sample.
• Sound transmission loss measurement using the impedance tube (ASTM E2611 / ISO 10534-2 / HRN EN ISO 10534-2 – for small samples) – for small fabric samples (typically 30 mm to 100 mm in diameter), we use a four-microphone impedance tube to measure the normal incidence transmission loss. The test is performed over a frequency range of 100 Hz to 6400 Hz. We report the transmission loss (in dB) as a function of the frequency and the α coefficient.
• Sound transmission loss for fabrics with different weights and constructions (NTC 5600 – for comparative analysis) – we test fabrics of different weights (g/m²), thicknesses, and weave structures (e.g., plain weave, twill, nonwoven) to evaluate the effect of these parameters on the sound insulation performance. We report the STL values for each fabric and identify the optimum construction for acoustic insulation.
• Sound transmission loss at different angles of incidence (NTC 5601 – for the directional sound insulation) – for fabrics that may be used in different orientations (e.g., vertical curtains, horizontal acoustic panels), we perform the STL measurement at multiple angles of incidence using a rotating source or a directional test setup. We report the STL for each incidence angle.
• Effect of lamination and backing on sound transmission loss (NTC 5602 – for composite fabrics) – we test fabrics with and without a lamination (e.g., with a foam backing, a mass-loaded vinyl layer, or a felt layer) to evaluate the improvement in sound insulation provided by the lamination. We report the STL for each configuration and the improvement factor.

Sound Absorption Coefficient Testing – Evaluating the Energy Dissipation Properties of Fabrics

Sound absorption is the process by which sound energy is converted into heat and dissipated within the fabric. The sound absorption coefficient is a measure of the fabric's ability to absorb incident sound, and it is a critical parameter for acoustic fabrics used in walls, ceilings, and partitions. Our tests quantify the absorption performance of fabrics, which is required for the design of quiet spaces and for the certification of acoustic products in Croatia.

• Sound absorption coefficient measurement using the impedance tube (ASTM E1050 / ISO 10534-2 / HRN EN ISO 10534-2 – for normal incidence) – a small fabric sample (typically 30 mm to 100 mm in diameter) is placed in an impedance tube, and the transfer function between two microphones is measured. The normal incidence sound absorption coefficient (α) is calculated for each frequency (from 100 Hz to 6400 Hz). We report the α values, the maximum absorption frequency, and the absorption spectrum.
• Reverberation room method for sound absorption coefficient (ASTM C423 / ISO 354 / HRN EN ISO 354 – for large fabric specimens) – for larger fabric samples (e.g., curtains, wall coverings), we mount the sample in a reverberation room (a room with highly reflective surfaces). The reverberation time of the room is measured with and without the sample. The sound absorption coefficient (α) is calculated from the difference in the reverberation time and the area of the sample. We report the α values (in 1/3‑octave bands from 100 Hz to 5000 Hz), the noise reduction coefficient (NRC), and the sound absorption average (SAA).
• Sound absorption coefficient for acoustic curtains and drapes (NTC 5610 – for vertical fabric systems) – we test acoustic curtains and drapes in a reverberation room, with the curtain hanging in its typical vertical configuration. The effect of the fold ratio (the amount of excess fabric) on the absorption is also evaluated. We report the absorption coefficient, the NRC, and the effect of the fold ratio.
• Sound absorption coefficient for fabrics with different surface treatments (NTC 5611 – for the effect of coatings and finishes) – we test fabrics with different surface finishes (e.g., flame-retardant coatings, water-repellent treatments, or acoustic membranes) to evaluate the effect of these treatments on the sound absorption performance. We report the absorption coefficient for each treatment.
• Sound absorption coefficient at different mounting and air gap depths (NTC 5612 – for the effect of installation) – we test the fabric sample with different mounting configurations (e.g., direct mounting on a rigid wall, with an air gap behind the fabric, or with a mineral wool backing) to evaluate the effect of the installation on the acoustic performance. We report the absorption coefficient for each configuration and the optimal air gap.

Noise Reduction and Attenuation Testing – Evaluating the Practical Sound Reduction Performance

In addition to the laboratory measurements, we perform practical tests that simulate the real-world use of the fabric, such as the reduction of speech transmission through a curtain, or the attenuation of noise from a machine enclosure. These tests provide a direct measure of the fabric's performance in the intended application, which is essential for the certification of acoustic products in the Croatian market.

• • Speech transmission reduction test (NTC 5620 – for acoustic curtains and partitions) – we place the fabric sample between two rooms (or in a simulated setting) and measure the reduction in the sound pressure level of a standard speech signal (e.g., pink noise or a male voice) as it passes through the fabric. The speech intelligibility index (STI) and the reduction in the A‑weighted sound pressure level are measured. We report the speech transmission reduction (in dB) and the STI improvement.
  • Noise reduction of an acoustic enclosure (NTC 5621 – for machine and equipment covers) – we measure the sound pressure level of a loudspeaker (or a machine) with and without a fabric cover (or an acoustic curtain). The reduction in the A‑weighted sound pressure level (in dB) is measured at specified positions around the source. We report the noise reduction and the insertion loss of the cover.
  • Insertion loss of a fabric panel (NTC 5622 – for the acoustic screen performance) – we place the fabric panel (or an acoustic curtain) between a sound source and a measurement position, and we measure the insertion loss (the reduction in the sound pressure level with the panel in place) as a function of the frequency. We report the insertion loss curve and the overall reduction (in dB).
  • Speech privacy and confidentiality assessment (NTC 5623 – for the office and open‑plan spaces) – for acoustic fabrics used in office partitions and sound-absorbing panels, we evaluate the privacy level by measuring the speech transmission loss and the sound absorption, and by calculating the privacy index (e.g., the Speech Privacy Potential). We report the speech privacy index and the classification.
  • Sound attenuation for automotive interior fabrics (NTC 5624 – for the vehicle acoustic performance) – we measure the sound attenuation of the fabric (or the fabric system, including the foam backing) in a vehicle interior simulation, using a speaker and microphones placed inside a mock‑up. We report the reduction in the interior sound pressure level and the improvement in the speech intelligibility.

Environmental and Durability Testing – Evaluating the Acoustic Performance after Aging and Exposure

Fabrics can lose their acoustic performance over time due to aging, wear, contamination, and exposure to humidity, temperature, and UV radiation. Our environmental and durability tests simulate these conditions to evaluate the long‑term stability of the acoustic properties and to ensure the reliability of the product in the diverse Croatian climate (continental, coastal, and mountainous regions).

• Acoustic performance after thermal aging (ASTM D573 / ISO 188 / NTC 5630 – for the fabric material) – we age the fabric sample in an oven at a specified temperature (e.g., 70 °C) for a specified duration (e.g., 7, 14, or 28 days), and then we re‑measure the sound transmission loss and the sound absorption coefficient. We report the change in the acoustic properties (in %) and the retention of the performance.
• Acoustic performance after humidity and moisture exposure (ASTM D2247 / NTC 5631 – for the effect of moisture) – we expose the fabric sample to a high‑humidity environment (e.g., 40 °C, 95 % RH) for a specified duration (e.g., 7 days), and then we re‑measure the acoustic properties. We report the change in the acoustic performance and the visual condition of the fabric.
• Acoustic performance after UV exposure (ASTM G154 / NTC 5632 – for the outdoor and sun‑exposed applications) – we expose the fabric sample to UV radiation (UVA-340) and condensation cycles for a specified duration (e.g., 500 hours), and then we re‑measure the acoustic properties. We report the change in the acoustic performance and the change in the color (ΔE*).
• Acoustic performance after abrasion and wear (ASTM D4966 / NTC 5633 – for the effect of surface wear) – we subject the fabric sample to a specified number of abrasion cycles (e.g., 10,000 cycles using the Martindale tester), and then we re‑measure the acoustic properties. We report the change in the acoustic performance and the surface condition.
• Acoustic performance after washing and cleaning (NTC 5634 – for the washable and cleanable fabrics) – we wash the fabric sample (according to the manufacturer's instructions, or using a standard wash cycle) and then we re‑measure the acoustic properties. We report the change in the acoustic performance after the washing and the dimensional stability.

Complementary Tests – Physical and Mechanical Characterization of the Fabric

To understand the relationship between the acoustic performance and the physical properties of the fabric, we perform a series of complementary tests, including the measurement of the thickness, the density, the air permeability, and the tensile strength. These tests are essential for the design of acoustic fabrics and for the optimization of the production process.

• Thickness measurement (ASTM D1777 / ISO 5084 / NTC 5640 – for the fabric thickness) – we measure the thickness of the fabric (in mm) under a specified pressure (e.g., 1 kPa) using a thickness gauge. We report the average thickness and the thickness variation.
• Fabric weight and density (ASTM D3776 / ISO 3801 / NTC 5641 – for the mass per unit area) – we measure the mass of the fabric sample (in g) and we calculate the fabric weight (in g/m²) and the density (in g/cm³) from the thickness. We report the fabric weight and the density.
• Air permeability measurement (ASTM D737 / ISO 9237 / NTC 5642 – for the flow resistance) – we measure the air permeability of the fabric (in m³/m²·min or L/m²·s) using a constant‑pressure air permeability tester. The air permeability is correlated with the sound absorption coefficient (materials with higher flow resistance generally have higher absorption at low frequencies). We report the air permeability and the flow resistance.
• Tensile strength and elongation (ASTM D5034 / ISO 13934 / NTC 5643 – for the mechanical strength) – we measure the tensile strength (in N or kN/m) and the elongation (in %) of the fabric in the warp and weft directions. We report the tensile properties and the correlation with the acoustic performance.
• Surface roughness and texture analysis (NTC 5644 – for the influence of the surface finish) – we use a surface profilometer or a laser scanner to measure the surface roughness (Ra, Rz) of the fabric. The surface roughness can affect the sound absorption, especially at high frequencies. We report the roughness parameters and the correlation with the acoustic performance.

Test Report and Recognition in the Croatian Construction, Automotive, and Industrial Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (sound level meters, microphones, impedance tubes, and reverberation rooms) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the fabric sample (manufacturer, fiber composition, weave, weight, thickness, and intended application).
• Detailed description of the test methods applied (ASTM/ISO/EN/HRN EN/NTC standards, test conditions, and measurement configurations).
• Numerical results: sound transmission loss (dB), weighted sound reduction index (Rw), sound absorption coefficient (α), noise reduction coefficient (NRC), sound absorption average (SAA), air permeability (m³/m²·min), and change in acoustic properties after aging (%).
• Graphical data: STL vs. frequency curves, absorption coefficient vs. frequency curves, and insertion loss spectra.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ISO 354, EN ISO 11654, HRN EN ISO 11654, and the requirements of the Ministarstvo graditeljstva for building acoustics).
• Recommendations for fabric selection, design optimization, and installation practices to achieve the required acoustic performance.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98-3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo graditeljstva i prostornoga uređenja for building acoustics compliance, by the Državni inspektorat for market surveillance, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of textiles and acoustic fabrics. Additionally, we offer consulting services for the design of acoustic textiles, the selection of fabrics with optimal acoustic properties, and the implementation of quality control programs, contributing to the acoustic comfort, safety, and sustainability of buildings, vehicles, and industrial environments in the diverse Croatian market, from the coastal tourist facilities to the continental manufacturing and industrial sectors.