Differences in SNR & NRR

Written by mark fitzpatrick
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Differences in SNR & NRR
Ageing and years of noise pollution can reduce quality of hearing. (Jupiterimages/BananaStock/Getty Images)

Noise reduction is an important health concern for every person. Hearing loss can come from external factors such as noise pollution or from infections or degenerative hearing conditions. One way to avoid hearing damage is to purchase hearing protectors: devices that reduce the sound that comes into your ear. However, there are different health codes that a consumer may have to take into account before purchasing such a device.

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The Noise Reduction Rating, or NRR, is a rating given to hearing devices in the United States and also Canada. The NRR is given in the United States because of special regulations the U.S. gives to hearing devices. The offices of the Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA) regulate the safety and reliability of the noise reduction products with an NRR rating.


The NRR is only given around North America with the United States and Canada. The other central noise reduction rating system is the Single Number Rating, or the SNR. SNR is the noise reduction rating given to products bought and sold in the European Union. Although both rating systems are designed to rate products based on their ability to stop noise, the SNR is essentially different and has different values compared with the NRR.


The NRR is a general noise reduction rating. In other words, the NRR is used for a device in all noise settings. For example, an earplug, under the guidelines of the NRR is going to have one type of NRR rating. However, the SNR rates each noise reducing device to a particular environment. SNR ratings utilise extra codes for high-frequency, mid-frequency and low-frequency noise environments. So, one type of earplug will have a certain SNR rating if it is used for construction sites while another will have a different rating if the earplug is used for office environments.

Lab Results

The NRR and the SNR also use different laboratory experiments to calculate their sound ratings. Random test subjects are given the devices by noise reduction companies. The test subjects are then told to listen to different decibel levels of noise. The random test sample population is asked if they hear the noises at certain levels. Calculating out the overall statistics, the NRR and SNR governing bodies are able to produce the general reduction rating for any device. However, because the SNR must calculate for environment, the same test subjects are told to listen to certain noises in hypothetical noise environments, such as loud construction sites. This, statistically, creates two statistical models for the SNR, while the NRR only has one.

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