What is the difference between SNR and NRR ratings?

by don campbell

The difference between SNR and NNR for earplugs lies in the region, standard, and method used to calculate the amount of noise reduction provided by the hearing protection. Here’s a breakdown:

🔹 SNR (Single Number Rating)

  • Used in: Europe and countries following the EN 352 standard.

  • Standard: Based on ISO 4869.

  • Purpose: Indicates the average level of noise reduction in decibels (dB) across a range of frequencies.

  • Application: To estimate actual protection, you subtract the SNR value from the noise level.
    Example: 100 dB noise – 25 dB SNR = ~75 dB exposure.

🔸 NNR (Noise Reduction Rating)

  • Used in: United States, regulated by the EPA.

  • Standard: Defined by ANSI S3.19.

  • Purpose: Also measures average noise reduction in dB, but with different lab testing methods and assumptions.

  • Application: More conservative. OSHA recommends a derating:

    • Subtract 7 dB from the NNR,

    • Then reduce the result by 50% (to account for real-world use).

    • Example: NNR 30 → (30 - 7) / 2 = ~11.5 dB actual protection.

⚖️ Summary Comparison

Feature SNR NNR
Region Europe United States
Standard EN 352 / ISO 4869 ANSI S3.19
Real-world use Often taken as-is or with minor adjustments Typically derated for realistic use
Test Method Frequency-weighted average with real-ear attenuation Lab-based, sometimes overestimates
Values Typically slightly higher than NNR Often more conservative after derating

✅ In Practice

  • If you’re choosing earplugs internationally, don’t directly compare SNR to NNR.

  • Always apply the proper adjustment based on the regulatory body or safety guidelines for your region.

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