SNR vs HML: How to Choose Hearing Protection
Hearing protection is not simply a case of choosing the highest number on the packaging. SNR and HML are two ways of describing how much sound a hearing protector can reduce in laboratory testing, but they are used in different ways.
This guide explains the difference so you can compare earplugs and ear defenders more confidently. The correct choice should always follow a suitable workplace noise assessment, the product instructions and current workplace safety guidance.
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What does SNR mean?
SNR stands for Single Number Rating. It gives one general attenuation value in decibels and is useful for making a quick comparison between hearing protectors.
A higher SNR does not automatically mean that a protector is the right choice for every noise. SNR is a simplified laboratory figure and does not describe how the protector performs at every frequency, how well it fits the wearer or how consistently it will be worn.
What does HML mean?
HML gives a more detailed view of attenuation at three frequency ranges:
| Rating | Frequency range | Why it matters |
|---|---|---|
| H | High frequencies | Useful when the main noise is higher-pitched. |
| M | Medium frequencies | Useful for many general industrial noises. |
| L | Low frequencies | Important where machinery or other sources produce deeper, lower-pitched noise. |
HML can be more informative than SNR when the noise has a strong frequency pattern. The manufacturer's technical data may show the H, M and L values alongside the SNR.
SNR and HML compared
| Measure | Best used for | Limitation |
|---|---|---|
| SNR | A quick general comparison between hearing protectors. | It reduces a complex frequency profile to one number. |
| HML | Comparing protection where the noise frequency is known or distinctive. | It needs more information about the noise and the protector. |
How to choose hearing protection
- Identify the noise. Use a suitable noise assessment rather than relying only on a rough guess or a conversation-distance test.
- Check the product data. Compare the SNR and, where available, HML values for the protector.
- Avoid choosing by rating alone. The protector must be suitable for the task, compatible with other PPE and comfortable enough to be worn correctly for the full exposure period.
- Check communication and alarms. Excessive attenuation can make speech, warning signals, vehicles or other important sounds harder to hear.
- Train users and check fit. Earplugs need the correct insertion and fit, while ear defenders need a good seal around the ear. Hair, glasses, helmets and other PPE can affect that seal.
Should you choose earplugs or ear defenders?
Earplugs can be lightweight and convenient, especially in warm environments or where helmets and other headwear are worn. Ear defenders can be easier to fit consistently and may be more practical for intermittent use, although the seal can be affected by glasses, hair or other equipment.
The right option depends on the noise, the working environment, compatibility with other PPE, the wearer and the results of the risk assessment. Some situations may require combined protection, but do not add SNR figures together without competent advice.
Hearing protection is part of a wider noise-control plan
Hearing protection should not be used as a substitute for reducing noise at source. Where possible, start with eliminating or reducing the noise, isolating machinery, improving workplace controls and limiting exposure. Use hearing protection as part of the overall control plan when a remaining risk requires it.
For more help, read our workplace noise guide and earplugs versus ear defenders guide.
Important reminder
This guide is general information and is not a substitute for a competent noise assessment, current workplace regulations, manufacturer instructions or your organisation's hearing-conservation policy. Check the product's relevant EN352 information and technical data before selecting hearing protection for a specific task.