I completely understand that everyone isn’t as passionate about sound and acoustics as I am. I also get that sound rating systems may be perceived as a dry topic for many. But I promise you that if you have an acoustic problem that led you to read this article or chat with me on the phone, your eyes won’t glaze over and you’ll appreciate the knowledge.

Here’s the thing, there are just so many products to address noise these days that you can’t be confident knowing you’re buying the right thing without understanding NRC ratings. When you’re searching for acoustic solutions, you surely see NRC ratings thrown around. If you make a purchase without knowing what they are, you might be disappointed with what you bought. I’m here to save you from that frustration. I want my customers to really understand what their options are.

In this article, I’ll discuss everything you need to know about NRC ratings, including what they are and how they work. Plus, I’ll share a few acoustic solutions that you might find helpful.

What is an NRC Rating?

NRC stands for “noise reduction coefficient.” An NRC rating is determined by a third-party laboratory that essentially issues a percentage grade that represents a specific panel’s ability to reduce noise. Simply put, the rating represents the percentage of sound captured by a product’s surface.

Sound Absorption and Transmission

Sound Absorption and Transmission

How Does an NRC Rating Work?

Ratings are typically expressed in decimals from 0 to 1, where 0 represents 0% (meaning the product absorbs sound) and 1 represents 100% (meaning the product absorbs sound). So, for example, if a panel has an NRC rating of .85, that means that roughly 85% of the sound that hits that panel’s surface will stop there.

We even have products that can exceed a 1 rating, getting as high as 1.15 (meaning the product can absorb or reflect 115% of sound). While that might seem impossible, the ratings are calculated by scoring all the surfaces of a given product. So, for example, when they score the front, back, and sides of a panel, then add those ratings together, the total reflective capabilities can exceed a 1.0 rating.

So, every product that has ever been created (even ones that aren’t meant to be soundproof) has an NRC rating. Fun fact: even people have an NRC rating! How is that possible? Well, it all comes down to how NRC ratings work.

When you use a product with a lower NRC rating (for example, our AlphaSorb® Designer Premium Acoustic Felt Wall Panels have a .5 sound rating), you need to combine them with other acoustical solutions to get the balance. You also have to cover a much wider surface area than you would with products with higher ratings.

NRC Rating Charts

Every product we offer has a specific NRC rating chart that explains the NRC rating of that particular product, along with additional sound ratings based on individual frequencies. To better understand these charts, it’s also important to have a little understanding of how frequencies impact NRC ratings. So, let’s talk about that, too.

Sample NRC ratings chart
Sound Absorption (Hz) — FR701 Fabric Wrapped Panel
Thickness 125 250 500 1000 2000 4000 NRC
1″ 0.14 0.27 0.80 1.11 1.14 1.14 0.85
2″ 0.40 0.74 1.24 1.25 1.22 1.14 1.10

How Does Sound Frequency Affect an NRC Rating?

When we talk about NRC ratings, we have to talk about the role that sound frequencies play in them. The lower the sound frequency, the lower the pitch and the larger the sound wave. The opposite is true for higher frequencies, which have a high pitch and a smaller sound wave. Frequencies are typically broken down like this:

  • 125 Hz: This is a low frequency, most comparable to a helicopter going overhead or a truck driving by your house.
  • 250 Hz: This is a low frequency, most comparable to household appliances running, like a lower level on a blender.
  • 500 Hz: This is a mid-range frequency, most comparable to most adult male voices.
  • 1,000 Hz: This is a mid-range frequency, most comparable to most adult female voices.
  • 2,000 Hz: This is a high frequency, most comparable to the upper end of a piano, a violin, and children’s speaking voices.
  • 4,000 Hz: This is a super high frequency, most comparable to the highest note on a piano or a small child screeching.

NRC-rated products will do a better job of absorbing higher pitches than lower pitches. It doesn’t matter what product you’re talking about. It’s just easier to absorb or block a high frequency than to absorb or block a low frequency. It all comes down to the bandwidth of the sound wave.

For example, a kick drum falls within the frequency range between 65 hertz and 125 hertz. The sound wave for that frequency can be up to 14 feet long. As acoustic consultants, our jobs are to block sound waves from valley to valley. So, when you’re dealing with a large sound wave, it will be much more challenging.

Conversely, the high-pitched hum of a dishwasher has a sound wave that might be as small as 6 inches. In comparison, it’s no wonder why it’s more difficult to block sound waves at lower frequencies. Those are just a few of the factors that contribute to an NRC rating, which is an average of sound blocked across the frequency band.

Blocking Lower Frequencies

It can be a serious challenge to block lower frequencies. As we mentioned above, the sound waves produced by lower frequencies are much larger than the ones created by higher frequencies. Fortunately, we have a few tricks up our sleeves that simplify blocking lower frequencies.

Offset Mounting

If you offset a panel two inches off the wall instead of making it flush with the wall, it creates an air gap that increases the effectiveness of sound absorption. This type of installation method can be incredibly useful for blocking lower frequencies.

Bass Traps

AlphaSorb Acoustic Foam Bass Trap - 2' Convoluted in Natural White

AlphaSorb® Acoustic Foam Bass Trap – 2′ Convoluted in Natural White

Many bass traps are specifically designed to create that extra air gap, which makes them super effective at blocking lower frequencies. Our AlphaSorb® Acoustic Foam Bass Trap is an excellent product that provides maximum broadband absorption to create crisp listening environments.

Hanging Clouds

Diamond Credit Union Bank lobby area using AlphaSorb clouds in ceiling.

Diamond Credit Union Bank lobby area using AlphaSorb® clouds in ceiling.

Hanging clouds is another method for blocking lower frequencies, and it works using the same principles as offset mounting. In fact, our AlphaSorb® Fabric Wrapped Acoustic Ceiling Cloud panels are an excellent option for blocking lower frequencies. Plus, they come in a wide range of colors and styles.

Sound Absorption vs. Sound Blocking

What are the differences between sound absorption and sound blocking (or soundproofing)? This is a question we get all the time, so it’s important to discuss the differences between them.



Sound Absorption

Sound absorption is about reducing the reverb inside a room as much as possible. It’s not so much about blocking sound as it is about improving the sound quality within the space. Sound absorption is measured with an NRC rating.

Sound Blocking

On the other hand, sound blocking, also called soundproofing, is about containing sound. When you’re trying to soundproof a room, your goal is to make sure that none of the sound created within the room gets out and none of the sound produced outside the room gets in. Sound blocking is measured with an STC rating.

Looking for High-Quality Acoustical Solutions?

No matter what NRC rating you’re looking for, Acoustical Solutions has something for you. Our products are created by expert sound engineers who understand exactly what you’re looking for when you want to soundproof your home or business.

Contact us today to learn more!

To learn more about how Acoustical Solutions can solve your noise control problems, use our contact form, call one of our Acoustical Sales Consultants at (800) 782-5742, or visit us on the web at acousticalsolutions.com.