Acoustics, Noise Reduction and NRC Ratings Explained

When looking into sound-absorbing solutions for architectural spaces, Noise Reduction Coefficient, or NRC rating, is the gold-standard the industry uses to rate different materials, products and applications. On the surface the rating is relatively simple: A higher rating means better performance.

Easy peasy, right?

It may look that simple at a glance, however, there is a little more science behind the NRC rating than “more must mean better.” Learning a little more about NRC ratings will go a long way when it comes to acoustical considerations.

A Brief Overview of Acoustics

When it comes to acoustics, it’s helpful to visualize a sound wave and its interaction with surfaces.

Once a sound wave is produced, it interacts with the different surfaces in the space. Each material will affect that sound wave in a different way.

Reverberation is the reflectiveness of a sound after it is produced and the ensuing decay, or reduction in the sound, as it continues to be absorbed by objects in any space. In other words, how long a sound lingers. It’s ultimately the result of how a sound wave interacts with the materials within a space and their relative absorption or reflection.

Reverberation isn’t good or bad, it’s a matter of what level of reverberation is appropriate for the space. A room or space that is made for projecting music, for example, will benefit from more reflective surfaces, thus higher reverberation. A room that requires speech intelligibility, like a classroom, needs lower reverberation, thus more sound-absorbing surfaces.

Sound reflection (pictured left) is when sound waves bounce off a surface nearly perfectly. Perfect reflection of a material means that material does not reduce the sound wave on contact. When we think of sound reflection, we think of hard surfaces – like glass or wood.

Sound absorption (pictured center) is the dampening or reduction of a sound as it interacts with the material. Effective sound-absorbing materials are highly porous, like PET felt, natural wool or building insulation. The porous nature of the material traps the sound wave and the energy of the sound wave dissipates, reducing the noise.

Sound blocking (pictured right) and sound-absorption often get confused. Sound blocking refers to the complete obstruction of sound through a partition, surface or material. Sound blocking stops sound waves from entering and leaving a room. These applications are used differently than sound absorption materials. For example, sound-blocking materials are largely used for sound-proofing a space (like SCIF room or any other area where conversation security is a concern).

What is an NRC rating?

Noise Reduction Coefficient is a value between 0.0 and 1.0 that describes the sound-absorbing performance of a material. NRC ratings are used to measure the effectiveness of any given material at absorbing sound.

All materials (from steel to bricks to pillows) inherently have an NRC rating. An NRC rating of zero is perfectly reflective and absorbs no sound (think concrete or glass with almost perfect sound reflection). An NRC rating of 1 is perfectly absorptive. A material can achieve an NRC rating higher than 1, however, this is a testing limitation. More on that in our webinar below.

Want a little more explanation? Check out our webinar!