Jul 2nd 2019

Specifying Acoustics: Sorting Through NRC Ratings Noise


For architects and interior designers, understanding how to sort through the wildly varying NRC ratings and claims is imperative to identify the quality and value of acoustics. With increased awareness of how beneficial acoustics are for architectural interiors, the more challenges designers face when it comes to specifying quality acoustics for their next project. Acoustic materials are complex in design, and it is advised to be aware of how the rating is presented when choosing your acoustic design elements. While comparing apples to apples with NRC ratings, data can vary from product to product and configuration to configuration.

By working within the acoustics industry, our Kirei team decided to put their research skills to the test to determine the different ways NRC can be presented to designers and how to apply this information to make good decisions.

But First, Let’s Cover the Basics

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NRC or Noise Reduction Coefficient is a measurement to determine the absorption properties of an object. We want to know exactly how well an object can absorb and reflect various soundwaves when it comes to the design of interior spaces, and implementing NRC is the ideal method in calculating the acoustic results.

NRC ratings vary on a scale of 0 to 1. A rating of 0 means that the object is completely reflective and absorbs no sound, such as a rock. On the other hand, a rating of 1 can tell you that the object is perfectly absorptive or in this case, absorbs all sound.

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With the scale ranging from rock to sponge, there is plenty of room in between for a variety of acoustic materials. This is where NRC ratings come into play, but keep your eye out and your ears open for how the rating is presented. Sometimes, the NRC can be presented in a misleading way.

The “Cherry Picking” Acoustics Trap

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Having a fluid rating system makes specifying acoustics a whole lot easier, no doubt. One problem that several designers run into is the matter of determining whether or not a product’s NRC rating is legitimate. With deceptive information spreading like wildfire, manufacturers are occasionally “cherry picking” the best scores based on misleading information.

To better understand how NRC is calculated, a product is tested for a total of 6 key wavelengths, and the average number of those tests determines the true NRC. However, it is becoming more and more common for manufacturers to select the better ratings from the test, rather than to just select the overall average.

Different Strokes for Different Folks

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A truthful NRC rating is also important in determining the product need based on what it will be used for. An elementary school gymnasium has acoustical issues that greatly differ from the noise that can be heard in a factory where heavy machinery is operated.

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It is important to know that not all NRC ratings are created equal. Since NRC is based on averages across 6 different wavelengths, two acoustic materials with the same ratings may not deliver the same value. This is where looking at the specification sheets and studying the overall wavelength results can help you make a “sound” decision, keeping in mind the specifics of your project.

Know All The Facts With Air Space

When it comes to specifying acoustics, it is common knowledge amongst architects and designers that air gaps create deeper absorption. With this information, it has been found that during NRC testings, acoustic suppliers sometimes incorporate air space to raise their NRC ratings.

It begs the question however, what is unethical about this method, especially if we know that it is an alternative way to help absorb sound? The problem doesn't exclusively lie with air spaces, but we have found that at times that the final ratings were occasionally determined with unreasonably large air gaps. We know the realistic range an air gap should cover, and when it comes to cutting hundreds of square feet from your space, it would most likely be perceived as an irrational decision.

Be on the lookout for how much air space was actually determined at testing for the specific acoustic material, and compare it to the specifics of your project. Otherwise, you may end up with unsatisfactory acoustic results.

Is there an NRC higher than 1?

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Ratings over 1? You may think, “How is that possible? I’ve never heard of such a thing!” Well, not to burst your bubble, but it’s definitely not a form of black magic-- instead, it’s a simple math trick. The reality is that an acoustic panel, no matter the size, has a surface area plus the edges.

While calculating NRC ratings, some people decide to include the edges in the equation. Don't let this mislead you into thinking the material is perfectly absorptive, as having a rating above 1 actually skews the overall perception of the quality.

Sure, we know that thicker materials will absorb more sound. However, we must get down to the nitty-gritty details to determine what the actual NRC rating is-- based on the surface material WITHOUT the edges to truly understand its absorbing capabilities.

The “Kirei” Way

Kirei chooses honesty and transparency, knowing that the quality of our product will speak volumes once the truth becomes more prominent as these projects are developed with the acoustics of sub-par quality.

Architects and designers deserve to know the truth on how NRC is calculated, how to choose the right materials for a specific space, and how to identify true quality over misleading claims.

With our wide selection of PET products, we are sure to have a specifically tailored acoustic solution for your needs. Feel free to reach out to one of our Kirei representatives today to get more information on our NRC ratings and product options.

Contact your Kirei rep to learn more about our quality acoustic elements!

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