Level-dependent ear defenders incorporate an electronic sound reproduction system, enabling the wearer to hear safe ambient sounds while protecting against dangerous noise.
Low-level sounds are detected by a microphone and relayed to a loudspeaker inside the ear defender cup. During high-level noise, the electronic circuit is deactivated, and the product’s passive attenuation provides protection.
This allows the wearer to hear their colleagues, warning sounds and approaching vehicles while offering protection against high noise that can damage the hearing.
The EN 352-4 standard sets out requirements for level-dependent ear defenders. Products must meet EN 352-1 for headband ear defenders, or EN 352-3 for helmet / faceshield mounted ear defenders, as appropriate. Ear defenders are tested for passive performance, along with assessment of headband force and durability, and supplied with full attenuation data including SNR levels.
Additionally, the level-dependent function is tested with three noises (H, M, L) to determine criterion levels.
What are criterion levels?
The criterion level specifies the maximum sound pressure of external noise for each test frequency in decibels (dB) before the level-dependent hearing protector sound restoration circuit exceeds 85 dB(A) at the ear.
Requirements vary for products intended for use against impulse-type noise risks only and those which can also be used for continuous high noise.
Products for impulse-type noise only:
- Minimum criterion level (H) = 85 dB(A)
- Minimum criterion level (M) = 85 dB(A)
- Minimum criterion level (L) = 85 dB(A)
Products for impulse and continuous noise:
- Minimum criterion level (H) = 97 dB(A)
- Minimum criterion level (M) = 96 dB(A)
- Minimum criterion level (L) = 94 dB(A)
What is the difference between continuous and impulse noise?
Continuous noise describes extended or constant high-level sound, whereas impulse-type noise is characterised by short duration high-level peaks. Impulse noise can present a great degree of risk, as the sound level can be higher than continuous noise, and the short, spontaneous nature of exposure can mean the appropriate controls are overlooked.
Level-dependent hearing protectors can offer the ideal solution for impulse noise risks, attenuating harmful noise while amplifying low-level sounds such as speech and warning signals.
If both continuous and impulse noise hazards are present, it is important to ensure hearing protectors are suitable – some level-dependent hearing protectors are intended for protection against impulse noise only.
High-performance protection
Sonis® Comms provides level-dependent attenuation for continuous and impulse-type noise risks, offering the highest SNR level for communication ear defenders.
The Sonis® Comms Headband range provides attenuation to an SNR of 34dB.
Sonis® Comms Mounted are certified compatible with JSP EVO® helmets and EVOGuard® browguard systems for an SNR of 30dB.
With criterion levels over 110dB for H,M,L test frequencies, Sonis® Comms headsets provide level-dependent attenuation suitable for use in impulse and continuous noise environments.
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