Page 1 - 3M Peltor Impulse Noise Report

Doc name Date Revision
Impulse noise and level dependent hearing protectors 20130319 a

Description Author Page 1 of 1
Memo Magnus Johansson, PhD
Senior Manager Research
and Test Lab
3M Personal Safety Division

Impulse noise and protection from level dependent hearing protectors

A level dependent hearing protector provides both passive attenuation and an electronically
controlled reduction of this attenuation. In environments with a moderate noise level, the
electronic circuit provides a ‘listen through’ signal from outside the cup. The level of the
signal is controlled with a volume control. In high noise level environments the ‘listen
through’ signal is limited to produce equivalent levels not higher than 82 dB(A). If the noise
level outside the hearing protector increases even more, the passive attenuation will
eventually not be sufficient. However, the level of the ‘listen through’ signal will not exceed
82 dB(A) equivalent level.

The electronic circuit, which controls the level dependent function, has an attack time
(reaction time) before limiting a loud noise. In 3M Peltor’s level dependent products the
attack time is less than 10 ms. A high level impulse noise with very short duration is not
primarily limited by the level dependent function during the attack time. However, there is a
limit for how loud signals the electronic circuit can reproduce. This limit is below
approximately 110 dB peak level. This means that there is a limitation in the output level,
which is not dependent on the attack time of the electronic circuit, but always limits the
reproduced sound.

The lower exposure action level for noise in working environments is 135 dB(C) for peak
levels according to the present EU Directive (2003/10/EC). The maximum reproduced sound
level from 3M Peltor’s level dependent products do not exceed 135 dB peak level, even
during the attack time.