NRC vs. CAC – The Acoustical Sound Absorption Debate

The two important properties to keep in mind when choosing acoustical ceiling panels are Noise Reduction Coefficient (NRC) and Ceiling Attenuation Class (CAC).

NRC refers to a surface’s ability to reduce noise by absorbing sound or the percentage of sound energy not reflected by the panel, which ranges from 0 to 1.0. The thickness and density of a product are two factors in calculating a Noise Reduction Coefficient. An acoustic ceiling product with a .95 NRC rating means that 95% of sound in the room is absorbed, while the other 5% is reflected.

CAC indicates the ceiling’s ability to prevent airborne sound from traveling between adjacent rooms when the dividing wall does not connect with the structural ceiling which ranges from 0 up to 40-45 for ceiling panels. Ceiling panels that have high CAC ratings (30 or greater) and are good for blocking noise from ceiling equipment noise, have a wide range of possible NRC performance, not necessarily maintaining quality sound absorption.

Sound absorption is a critical component of every room that will be occupied by people and, while lightweight, modular ceilings are not effective at blocking sound – they are, in fact, very good at absorbing it. Ceiling panels serve to absorb the noise in the room, preventing it from bouncing off surfaces and spreading through spaces and down corridors causing disruptions.

“Rockfon Optimized Acoustics™ provides a simple, straightforward approach to meet current acoustic standards, guidelines and criteria, while keeping on budget. With Rockfon ceilings you can optimize the ideal acoustic environment without compromising style or performance,” says Gary Madaras, PhD, ASA, INCE, Assoc. AIA, acoustics specialist at the Rockfon Group.

Rockfon offers an extensive portfolio of sound-absorbing, acoustic stone wool ceiling systems with NRC as high as 0.95. Their acoustic stone wool ceiling products include:

Rockfon Alaska®, with an NRC of 0.90, provides sound absorption for open plan offices, classrooms, retail and reception areas
Rockfon Medical Plus™, with an NRC of 0.90, provides sound absorption and superior hygienic properties for medical office buildings, acute care hospitals and eldercare residences
Rockfon Sonar®, with an NRC of up to 0.95, provides sound absorption for health care, education and open plan offices

To learn more about the benefits of Rockfon ceiling solutions, visit our website at

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