I’m sure by now you have come across something called an NRC rating during your soundproofing journey. I decided to investigate exactly what it is and have presented everything I learned in a simple-to-understand format in this post.
What is NRC? It is the percentage of sound a product or material is able to absorb within the confines of a space or room. NRC is measured on a scale of 0 to 1 where a rating of zero equates to negligible sound absorption and a rating of 1 equates to maximum sound absorption. It is mathematically represented by 𝛂 = 1 – (Ir/Ii).
In the equation mentioned above, Ir is the sound absorption coefficient for the reflected sound and Ii is the incident sound. If you want to learn more, make sure to check out this complete guide to engineering acoustics and sound absorbing materials.
What does NRC stand for?
NRC stands for Noise Reduction Coefficient.
What is the NRC scale?
The NRC scale consists of a rating from 0 to 1. It was designed many years ago a as standard way to determine how well a specific material absorbs sound within a room.
The noise reduction coefficient scale is based on the frequency range of audible sound. It covers the following frequency ranges: 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz.
It is important to consider low and high tones when soundproofing a room. This will help you make a decision on which product and materials to get in order to effectively reduce the noise.
What is a good NRC rating?
A good NRC rating for soundproofing is .65 or higher. Some may prefer a rating of .80 or higher. To give you a better understanding of this scale and what to expect, I have broken it down into 3 categories and placed into this table to help you better understand
| NRC Rating | Sound Reflection | Sound Absorption |
| 0 | 100% | 0% |
| 0.5 | 50% | 50% |
| 1 | 0% | 100% |
An NRC rating = 0 indicates perfect sound reflection and negligible sound absorption. An NRC rating of .5 indicates that half of the sound is reflected while the other half is absorbed. An NRC rating of 1 indicates negligible sound reflection and perfect sound absorption.
At an NRC rating of 0, the sound is reflected off a smooth surface and never absorbed. It simply bounces off your walls back into the room creating more noise.
At an NRC rating of .5, half of the sound is absorbed by foam panels, furniture, paintings, or carpet in a room while the other half gets dispersed back into the room. You will certainly notice a reduction in noise by it will not be perfect.
At an NRC rating of 1, all of the sound in a room is absorbed by soundproof material and products. You will notice significant reduction in noise, which will make the desired audio crystal clear.
Therefore, the higher the noise coefficient rating the better the material is at absorbing sound. The soundproofing capability of a specific product is directly proportional to its NRC.
Is it possible to have a noise reduction coefficient rating greater than 1?
Yes, it is possible to achieve an NRC rating greater than 1. This is due to the innovation of soundproof designs using both diffusive characteristics and absorptive characteristics to break up excess energy better.
These type of soundproofing designs are 3-Dimensional. They protrude into the room, which allows for sound to be absorbed by the product plus some of the space surrounding it. This makes it possible to achieve an NRC that is greater than 1.
An example of this could be stack fiberglass serveral inches thick placed a few inches from a wall. The sound is able to be absorbed from all sides of the fiberglass.
Why are products designed for NRC?
Products designed with noise reduction coefficients to help absorb excess energy in the room. This allows the audio to reach an intelligible level.
For example, have ever been in a gymnasium before where many people are talking? You will notice that it is difficult to hear what someone is saying. The noise level in the gymnasium is what makes audio unintelligible, or difficult to decipher.
The main goal of every soundproofing product is to reduce unintelligibility. If this does not happen then the sound cannot be deciphered successfully. Therefore soundproofing needs to be implemented in order to make the audio intelligible.
Products with high NRC displays a higher soundproof quality. This is essential information for the consumer, which can help them make a decision regarding whether or not to purchase the product.
What is sound absorption?
Sound absorption is the process of capturing the energy produced by noise with a certain material. It helps to make the desired audio more intelligible.
What happens to sound when it’s absorbed?
When sound gets absorbed, it quickly gest dissipated by the material capturing it. It can actually alter some of the initial energy molecules into heat if the soundproof medium begins to vibrate.
What material absorbs sound waves the best?
The best material that absorbs sound is dense and relatively soft. Any type of insulated material such as blankets or carpeting works well for absorbing sound waves.
Here is a list of material that does a great job of soaking up noise:
- Rubber mats
- Foam panels
- Soundproof blankets
- Soundproof curtains or thick drapes
- Large pieces of furniture
- Acoustic panels
- Filled bookcases
- Artificial plants
- Wall art and decor
- Mass loaded vinyl
What materials absorb sound the worst
There are some materials you should stay away from if you intention is to soundproof a room. I have listed the worst sound absorbing material below. These have very low noise coefficient ratings:
- Sheetrock
- Glass window
- Drywall
- Gypsum
- Steel
NRC rating chart
Below is the nrc ratings of materials that are commonly used. The NRC rating is entirely dependent on the type of product, structure, and density.
| Material | NRC rating |
| Sheetrock | .005 |
| Concrete | .35 – .7 |
| Drywall | .05 |
| Carpet | .35 |
| Acoustic panel (1”) | .80 – 95 |
| Acoustic panel (2”) | .95 – 1.2 |
| Mineral Fiber Ceiling Tile | Up to .95 |
| Gypsum | .06 |
| Wood | .15 |
| Plywood | .23 |
| Fiberglass | .75 |
| Regular glass | .02 |
| Steel | .1 |
Note that the NRC ratings of these may vary. This chart is simply an estimate for each material and may greater or less depending on how it is made and the type of material used.
For example, the NRC rating of ceiling tiles will vary by the the type of material used. Most commercial ceiling tiles are made of mineral fiber. However, there are ceiling tiles made of fiberglass with a higher NRC rating.
