An NRC (Noise Reduction Coefficient) rating is a single number that describes how much sound a material absorbs rather than reflects back into a room. It is averaged from lab-measured absorption coefficients, and higher numbers mean more absorption. Poor room acoustics are far more than an annoyance: sound reflecting repeatedly off hard surfaces builds into reverberation that degrades speech clarity, raises stress levels, and reduces concentration. Research has shown that noise can reduce both performance accuracy and working memory, with non-auditory effects including perceived disturbance, annoyance, cognitive impairment, cardiovascular disorders, and sleep disturbance. (WHO) The impact is particularly acute in learning environments. According to the Acoustical Society of America, in many U.S. classrooms, speech intelligibility is 75 percent or less, meaning listeners with normal hearing understand only three of every four words, which directly impairs comprehension and retention. Addressing these problems begins with understanding how acoustical materials are measured and selected, and the NRC rating is the most widely used starting point for that conversation.

Le coefficient NRC est calculé comme la moyenne arithmétique des coefficients d'absorption acoustique d'un matériau, mesurés à quatre fréquences moyennes (250 Hz, 500 Hz, 1 000 Hz et 2 000 Hz), arrondie au 0,05 près. À titre indicatif : le béton ou le verre non traités présentent généralement un NRC d'environ 0,02 à 0,05, la moquette standard se situe entre 0,30 et 0,55 selon la hauteur des fibres, et les dalles de plafond acoustiques suspendues classiques entre 0,55 et 0,75. Le revêtement BASWA Phon atteint un NRC de 0,80 à 30 mm et jusqu'à 1,00 à 70 mm selon la finition et l'épaisseur, ce qui le place parmi les finitions de surface les plus performantes pour les applications architecturales.

Les valeurs NRC doivent provenir d'essais effectués par un laboratoire tiers selon la norme ASTM C423, « Méthode d'essai normalisée pour l'absorption acoustique et les coefficients d'absorption acoustique par la méthode de la chambre de réverbération », publiée par ASTM International. Cet essai mesure la vitesse de décroissance du son dans une chambre de réverbération, d'abord vide, puis avec un échantillon normalisé du matériau installé, sur une gamme de fréquences, à l'aide de plusieurs microphones et haut-parleurs. On obtient ainsi un coefficient d'absorption pour chaque bande de fréquence, et la moyenne des quatre valeurs moyennes permet de calculer le NRC. Les conditions de montage utilisées lors des essais influencent directement les performances mesurées. Un matériau testé avec un espace d'air derrière lui, comme le montage E400 qui simule un plénum de 40 cm de profondeur, peut présenter une absorption supérieure à celle du même matériau testé directement sur une surface dure (montage A). Il est donc important de comparer des produits testés avec le même montage. Les systèmes BASWA sont testés selon la norme ASTM C423 dans les conditions de montage correspondant à leur installation : montage A, montage E ou les deux, selon le système. Chaque fiche d'essai précise le montage utilisé. Vous pouvez consulter la documentation de test tierce de BASWA sur notre page Données techniques .

Understanding NRC in isolation is useful, but it is most powerful when considered alongside the other acoustical ratings that govern how a space sounds and performs. NRC specifically addresses how much sound is absorbed within a room, reducing echo and reverberation time. It is a different measurement from the Sound Absorption Average (SAA), which averages 12 one-third octave bands from 200 Hz to 2,500 Hz, rounded to the nearest 0.01, and offers a more refined picture of a material's mid-frequency performance. NRC is also distinct from the Sound Transmission Class (STC), which measures how well a partition blocks sound from passing between rooms, and from the Ceiling Attenuation Class (CAC), which measures how well a ceiling system blocks sound from traveling through a plenum from one room to another. A well-designed acoustical environment typically requires attention to all of these metrics together, and the right combination depends heavily on how a space is used.

NRC is most appropriate for general-purpose spaces where speech noise buildup and reverberation are the primary concerns, including lobbies, open offices, reception areas, and classrooms. For spaces where the acoustical demands are more nuanced, such as recording studios, performing arts venues, or medical consultation rooms, it is advisable to examine the full frequency-by-frequency absorption data from ASTM C423 testing rather than relying on the averaged NRC alone. Results can also vary between laboratories, which is one reason why comparing products tested at different facilities requires careful interpretation. Because BASWA Phon and BASWA Natural are finished in the field as one continuous surface, they can follow flat, curved, and vaulted geometry without breaking into panels or grid. Whether you are designing a corporate headquarters, a school, a healthcare facility, or a private residence, NRC ratings, understood in context, are the foundation for making informed acoustical material decisions. Explore our portfolio to see how BASWA has been applied across these project types, or visit our continued education page to earn AIA learning units on acoustical design.