Sound Source: Understanding Ratings

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Sound Source: Understanding Ratings
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Hearing protector device packaging displays a series of rating numbers, including NRR, SNR and SLC80, What do these rating numbers mean?

Howard Leight hearing protectors are packaged to be shipped throughout the world. While customers in the U.S. are familiar with the NRR labeling required by the EPA, they may be a bit confused with packaging that includes other rating numbers. The following summary explains the rating numbers seen on Howard Leight packaging and in marketing materials.

NRR [Noise Reduction Rating]
This rating is used in the United States, and is accepted for use in a variety of other countries. The current range of NRRs available in the U.S. market extends from 0 to 33 decibels. Published by the U.S. Environmental Protection Agency in 1979, the NRR labeling requirement is a standardized format for all hearing protectors distributed in the U.S.* The EPA defines the type face size, font, wording and placement on the package for the NRR label. The chart showing mean attenuation values and standard deviations at each of the seven test frequencies (from 125 Hz through 8000 Hz) is also part of the labeling required by EPA.

SNR [Single Number Rating]
This rating number is used by the European Union and affiliated countries. Tests are conducted at independent testing laboratories, using test frequencies which are slightly different than those used for the NRR rating. In addition to an overall rating, the SNR further rates protectors in terms of the particular noise environments in which they will be used – H for high-frequency noise environments, M for mid-frequency, and L for low-frequency†. Note that the HML designation does not refer to noise level, rather the spectrum of the noise. For example, a protector might be designated with SNR 26, H=32, M=23, L=14. The estimated attenuation changes according to the noise spectrum of the environment in which the protector is to be worn.

SLC80 [Sound Level Conversion] – The SLC80 is a rating number used in Australia and New Zealand‡. It is an estimate of the amount of protection attained by 80% of users, based upon laboratory testing. Depending on the level of attenuation in the SLC rating, a classification is assigned to a protector: a Class 1 protector may be used in noise up to 90 dB, a Class 2 protector to 95 dB, a Class 3 protector to 100 dB, and so on in 5 dB increments.

Packaging will often show the SLC80, followed by the classification (i.e. SLC80 27, Class 5). Customers should not be concerned when they see several different attenuation ratings on a package. Each rating number is based upon differing test standards, test frequencies and calculation methods, and any given hearing protector generates different numbers depending on the rating method used.
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Footnotes:
* The EPA labeling standard is defined in Code of Federal Regulations (CFR) 40, Part 211, Subpart B – Hearing Protective Devices.
† The SNR rating and HML descriptors are defined in ISO 4869-2, Acoustics – Hearing Protectors.
‡ The SLC80 is defined in Australian/New Zealand Standard 1270:2002, Acoustics – Hearing Protectors.