ABSTRACT
Hearing protectors, unless specifically designed, attenuate the higher frequency sound
energy more than lower frequency energy. Because such a nonuniform attenuation characteristic
can be less than optimal for certain high-fidelity requirements, acoustically tuned
hearing protectors were developed. These include the ER-15 and the ER-25 earplugs
that-as the name suggests-provide a uniform attenuation of 15 dB and 25 dB, respectively.
To obtain different attenuation characteristics, modifications of these earplugs are
clinically possible, but they will lose their uniform attenuation property. Such earplugs
can be used in the performing arts and in industrial settings with noise levels below
100 dBA. The ER-20 (or HI-FI earplug) noncustom earplug also is available. Objective
techniques, such as microphone-in-real-ear (MIRE) and the use of acoustical test fixtures
(ATF), and subjective techniques, such as real ear attenuation thresholds (REAT),
are two valid methods for assessing the effects of hearing protection. Regardless
of the technique, the resulting data can be expressed in a single number rating scheme
such as the Noise Reduction Rating (NRR).
KEYWORDS
Attenuation - hearing protector - ER-15 - NRR - noise