User:GWei13/sandbox

Personal noise reduction devices[edit]
Personal noise reduction devices (HPDs) can be categorized into earplugs, earmuffs, and helmets .Earplugs or earmuffs which can block noise up to a specific frequency. Earplugs and earmuffs can provide the wearer with 10 dB to 40 dB of attenuation. However, use of earplugs is only effective if the users have been educated and use them properly; without proper use, protection falls far below manufacturer ratings. A Cochrane review found that training of earplug insertion can reduce noise exposure at short term follow-up compared to workers wearing earplugs without training. Higher consistency of performance has been found with custom-molded earplugs, but the skill of the impression taker and the depth of the mold is key. Because of their ease of use without education, and ease of application or removal, earmuffs have more consistency with both compliance and noise attenuation. For long-term wearing, earmuffs are often reported tight, hot, bulky, and heavy. Helmets are not commonly worn in occupational settings, because they primarily designed for impact protection. while helmets contain circumaural earcups or a dense liner to seal around the ears, they can reduce amount of noise exposure level at ear. However, HPDs have certain negative effects on auditory communications. To improve auditory perception and speech communication, some special HPDs designed. They may be passive (i.e., without powered electronics) and active HPDs (i.e., with powered electronics ). The most prevalent of the special passive HPDs are uniform and moderate attenuation devices and level-dependent devices. Active ear protection (electronic pass-through hearing protection devices or EPHPs) electronically filter out noises of specific frequencies or decibels while allowing the remaining noise to pass through

A personal attenuation rating can be objectively (also called physically) and subjectively (also called psychophysically )measured by using a hearing protection fit testing system. Current methods used in the field to estimate a personal attenuation rating (PAR) are: real-ear attenuation at threshold (REAT, ISO 2018), microphone in the real-ear (MIRE,ANSI 2018), and the alternating binaural loudness balance under headphones (Voix 2021).