What Is an NRC Rating? The Noise Reduction Coefficient Explained

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’s just so many products to address noise these days, 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.

NRC stands for “noise reduction coefficient.” It's a percentage grade for how much sound a material soaks up, issued by an independent test lab rather than by the company selling the product. The test itself is run in a laboratory reverberation chamber under the ASTM C423 standard.

The NRC number is an average of a material’s sound absorption coefficients measured at four mid-range frequencies — 250, 500, 1,000, and 2,000 Hz — rounded to the nearest 0.05. Those are the frequencies where most speech sits.

A rating of 0 means the surface reflects all sound and absorbs none, while a rating of 1 means it absorbs essentially all the sound that reaches it.

Every material has an NRC, including materials nobody designed with acoustics in mind. Your drywall has one. Your couch has one. You have one, which is part of why a packed conference room sounds so different from the same room empty.

A lower NRC rating isn't automatically the wrong choice, it just changes the math. Our AlphaSorb® Designer Premium Acoustic Felt Wall Panels have a 0.50 sound rating, but people like the look of the felt material. At 0.50 you need to cover considerably more wall, or pair them with another product, to land where a 0.90-rated panel would be on its own.

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.

Here's roughly where common materials land:

If you have a room that echoes, you generally want the surfaces you treat sitting at 0.75 or above, which is where our fabric-wrapped panels land. Every product page lists its own tested number, along with a chart breaking the absorption out frequency by frequency. That chart matters more than the single average, and I'll get to why.

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 longer the sound wave. The opposite is true for higher frequencies, which have a high pitch and a shorter sound wave. That difference drives almost everything about what a panel can and can't do.

NRC-rated products handle absorbing higher pitches better 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. This is true of every product, ours included, and it has nothing to do with build quality. It's the sound wave.

For example, a kick drum sits somewhere within the frequency range between 65 hertz and 125 hertz. The sound wave for that frequency can be over 10 feet long between peaks. To do anything about a wave that size, the material has to be thick, or off the wall, or both.

Conversely, the high-pitched hum of a dishwasher has a sound wave that might be as small as 6 inches long. An inch of fiberglass will easily absorb that.

In comparison, it’s no wonder why it’s more difficult to block sound waves at lower frequencies. A panel with a high NRC rating can still struggle with lower frequencies.

It can be a serious challenge to absorb sound at lower frequencies. As we mentioned above, the sound waves produced by lower frequencies are much longer than the ones created by higher frequencies. There are a few ways to get more low-end absorption out of a room without buying something exotic.

Pull the panel two inches off the wall instead of mounting it flush. This installation method can be incredibly useful for attenuating lower frequencies, as the air gap behind it improves low-frequency performance noticeably. Plus it costs you nothing but the standoff hardware. It's the cheapest upgrade in acoustics!

Sound Absorption is about what happens inside a room. It reduces reverb and echo so speech is clearer and the space stops feeling harsh. That's what the NRC rating measures.

On the other hand, sound blocking, also called soundproofing, is about containment. It keeps sound from getting out of a room or into one, which means mass, isolation, and sealing every gap. Sound Blocking is measured with an STC rating, and a high-NRC panel will do very little for it.

If you can hear your neighbor through the wall, panels are not your answer. If you can hear yourself three times over in your own conference room, they are.

Tell us the room dimensions, what the surfaces are made of, and what's making the noise. We'll tell you what NRC you need and how much of it, which is usually the part people underestimate. Sometimes the answer is that panels aren't what you need at all, and we'd rather say that up front than sell you a wall of them.

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 and we'll work through it.