Anyone who wants to plan or optimise rooms acoustically cannot avoid standardised acoustic parameters. Whether an office, classroom, catering establishment or public building, the acoustic quality has a decisive influence on well-being, concentration and speech intelligibility. To enable planners, architects and building owners to make well-founded decisions, the acoustic properties of materials are assessed using standardised measured values. Acoustic key figures such as NRC, αw and Rw are particularly relevant. Understanding these values creates the basis for a targeted choice of materials and sustainable acoustic planning.

NRC: The international reference value for sound absorption

The Noise Reduction Coefficient, or NRC for short, is an acoustic parameter widely used in Anglo-American countries to assess the sound absorption of a material. It is calculated according to ASTM C423 and is based on the mean value of the absorption coefficients at 250 Hz, 500 Hz, 1000 Hz and 2000 Hz.

The NRC value ranges between 0 and 1: a value of 0 means no sound absorption, a value of 1 means complete absorption of the incident sound energy. The NRC enables a quick comparison of different materials, but only represents a limited frequency range and should therefore be understood as a simplified guide value.

αw: The weighted sound absorption coefficient according to the European standard

In Europe, the weighted sound absorption coefficient αw has established itself as the key acoustic indicator. The measurement is carried out according to DIN EN ISO 354 in the so-called reverberation room. This involves analysing how much a material reduces the reverberation time of a room.

The αw value takes into account a broader frequency spectrum than the NRC and is calculated according to DIN EN ISO 11654 classified. It is particularly suitable for common rooms in which speech intelligibility and reverberation control play a central role. Typical applications include offices, classrooms, administrative buildings and catering establishments.

The higher the αw value, the more effective the material is at absorbing sound within a room.

Rw: Sound insulation between rooms

While NRC and αw describe the sound absorption within a room, the weighted sound reduction index Rw stands for the airborne sound insulation of building components. Typical components are walls, ceilings or windows.

The measurement is carried out according to DIN EN ISO 10140-2, the evaluation as a single value according to DIN EN ISO 717-1. The Rw value is given in decibels. The higher this value, the better the component prevents the transmission of sound between neighbouring rooms.

Rw is therefore a key acoustic parameter for structural sound insulation and for compliance with legal requirements.

Why standards and measurement methods are crucial

For reliable planning, it is not enough to look at just one acoustic parameter. The decisive factor is the standardised basis on which this value was determined. Only standardised tests provide comparable and reliable results.

Planners should therefore always check:

• According to which standard was measured
• If the test was carried out in the reverberation room
• Which frequency ranges were considered

Transparent manufacturer specifications create planning security and facilitate systematic acoustic optimisation.

Interaction of absorption and insulation

In practice, it is important not to consider absorption and insulation in isolation. Good room acoustics result from the interaction of both factors.

• Absorption reduces reverberation and improves speech intelligibility
• Insulation prevents sound transmission between rooms

Only when both objectives are taken into account can an acoustically comfortable room with a high quality of stay be created.

Conclusion

Acoustic indicators such as NRC, αw and Rw are key tools in building and room acoustics. They enable an objective assessment of materials and components and create a reliable basis for planning and implementation.

Anyone who interprets these parameters correctly and uses them in accordance with the standards lays the foundation for acoustically convincing rooms with a high quality of use.

Your next step to optimised room acoustics

Would you like to know which acoustic solution is the right one for your project? Our specialist consultants will be happy to help you select suitable systems and plan them in accordance with standards.

Get in touch with us for a non-binding consultation and improve the acoustics of your rooms sustainably and reliably with SAGER.