To help people choose the hearing protection that’s right for our needs, a variety of simplified numeric attenuation ratings were created. These ratings tell the buyer roughly how many decibels that a noise will be reduced by when heard through the hearing protection.
The two most common of these attenuation ratings are SNR and NRR. Both are denoted by a number of decibels (dB). In essence, the higher the number is, the more protection the product provides.
Both systems have their differences, so understanding them is important to making an informed decision when buying hearing protection.
Before we get into the two ratings, it’s important to understand the nature of the decibel measurement system and noise attenuation. When a barrier is placed between the ear and a noise source, the noise will be reduced in volume. Human perception of noise reduction and actual energy reduction are two very different things, however. Decibels are designed to reflect this.
One common scenario where this becomes an issue is when users decide to use earplugs and ear defenders at the same time. If you have some earplugs with an attenuation of 30 dB and some ear defenders with the same attenuation, both worn at the same time will not produce an attenuation of 60 dB. The power involved in a sound is roughly doubled every 3 decibels. So, in the previous hypothetical scenario, the actual attenuation would be roughly 33 dB.
SNR (Single Number Rating)
The Single Number Rating—or SNR for short—is the EU’s standard for showing the attenuation rating of hearing protection.
By far the most important difference between SNR and NNR for buyers is that SNR is determined by independent testing laboratories, not the manufacturer. Whilst it is unheard of for manufacturers to falsify test results, the testing standards are a lot more realistic than the highly-controlled lab tests used in the US.
SNR is often paired with another attenuation rating: the HML rating. The HML system attempts to give the user an idea of the attenuation provided by hearing protection at different frequencies: high, medium, and low. This allows the wearer to pick hearing protection when the noise environment is mostly dangerous at a specific area on the frequency spectrum.
Unfortunately, SNR is still slightly inaccurate to the real-world performance of a given product. To estimate the real-world performance, you can use an online calculator.
NRR (Noise Reduction Rating)
NRR is the SNR equivalent in the United States. It’s determined through a series of tests that are conducted by the manufacturer instead of an independent testing laboratory.
The testing procedure is sometimes very clinical, ensuring that test subjects have their hearing protection fitted properly. This often means that the test results overstate the real-world performance of the hearing protection. Corrections are applied to the calculation to provide a more useable real-world performance rating. This figure can be more inaccurate than SNR, however.
In the end, the NRR of a product is designed to accurately reflect the performance most people will achieve when the protection is properly fitted and tested in a laboratory setting. Real-world performance will almost always be lower due to the difference in noise frequency.
Put simply, SNR and NRR are two standards for measuring the attenuation of a hearing protection product. SNR is the EU standard, NRR is the US standard. The testing procedure is slightly different between them and the calculations involved are different. Both ratings are designed to determine a good estimate of real-world performance when the hearing protection is fitted properly in most real-world noise environments.
Since they are both designed to reduce the complexities of noise attenuation to a single number, actual performance will differ depending on a variety of factors. Different hearing protection solutions will perform better at different frequencies. It’s important to consider the noise environment that the protection will be used in.