In most countries, hearing protectors are required by law to be tested and labeled in a specific way. The idea is that by using a standardized measurement method and a straightforward, one-number rating, it should help users decide which hearing protector to choose. However, it turns that one number often doesn’t tell the whole story.
Hearing protectors sold in the U.S. must be labeled with a Noise Reduction Rating (NRR). The NRR is often a significant factor in purchasing hearing protectors and estimating at-the-ear noise exposures.