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Barriers to effectiveness[edit | edit source]
editFit[edit | edit source]
editA proper fit of the earmuffs on the head is essential to providing adequate hearing protection. Individuals will require earmuffs of differing sizes. This is especially important to remember when considering earmuffs for children. Muffs should make a good seal against the head and should fully cover the outer ear without pushing against the ears. Additionally, the headband should be the correct length to hold the cushions over the ears. Otherwise, sound can leak under the muffs and will reach the users' ears. Some wearers may use their earmuffs when hair is covering their ears or while wearing glasses. Prior to placement on the head, hair should be carefully pulled back and away from the cushions. Placing earmuffs over obstructing hair or safety glasses with thick frames may reduce the earmuff attenuation by 5-10 dB. Even eye-glasses with thinner frames can reduce the effectiveness of hearing protection by 3-7 dB.
One simple method for checking earmuff fit is to lift one or both muffs away from the head while in a noisy environment. If the noise is considerably louder with the adjustment, then the earmuffs are providing at least some degree of noise reduction.
Improper earmuff fit can cause discomfort, which in turn may cause the individual to avoid wearing the hearing protection device, reducing its effectiveness. Characteristics of a comfortable earmuff include: lightweight material, soft and removable circumaural cushions, low heat and humidity buildup, easy maintenance, reduction in low-frequency noise, no resonances of sound within the earcup, wide headband, and large enough earcups to allow for full coverage of the outer ear. If the individual finds the hearing protection device to be uncomfortable, he or she should explore other options for hearing protection, such as a different style of earmuff or earplugs. [1]
Structural Transmission
It is possible for sound to transmit through the earmuff materials, reducing the device's effectiveness. This transmission is primarily seen above 1000 Hz .[1]
Vibration of the Earmuff
In loud enough environments, the ear canal can vibrate, causing the air trapped inside the earcup to vibrate as well. This typically only occurs with low frequency noise, but can reduce the effectiveness of the hearing protection device. [1]
Readjustment
During the amount of time an individual wears earmuffs, the device can be jostled and displaced from the proper position that allows for the highest attenuation. This can be common in the workplace, as many individuals are in motion during the time they are wearing the hearing protection device. Moving the jaw while chewing or talking and perspiration are examples of ways in which readjustment can occur, causing the seal to be broken between the earcup and skin and allowing sound to leak in[2]
Deterioration[edit | edit source]
editIt is also important to consider the age and physical condition of earmuffs. Earmuffs should be inspected regularly for cracks and changes in shape or firmness. Headbands may also loose their tension or ability to properly adjust to the head, which could lead to a decrease in device effectiveness.Physical changes could create an opening to the ear, allowing sound through and reducing attenuation.
- ^ a b c Rawood, Vishakha (2011). Hearing Conservation: In Occupational, Recreational, Educational, and Home Settings. New York, NY: Thieme Medical Publishers, Inc. pp. 156–158.
- ^ Berger, Elliot (1980). "Hearing protector performance: How they work-and-what goes wrong in the real world". EARlog 5 – via Aero Company: Indianapolis, IN.