Earmuffs

Both items consist of a thermoplastic or metal head-band that fits over the top or back of the head, and a cushion or cup at each end to usually cover both ears.

[1] He reportedly conceived the idea while ice skating, and asked his grandmother to sew tufts of fur between loops of wire.

Because the ears extend from the sides of the head to gather sound waves, they have a high skin surface-area-to-volume ratio, and very little muscle tissue, causing them to be one of the first body parts to become uncomfortably cold as temperatures drop.

Earmuffs can be used to warm the ears only, avoiding overheating other parts of the body or trapping exhaust heat from strenuous movement.

Another type has two round earpieces made from a material that can produce heat, connected to a thick headband going around and behind the head.

[3] Pilots of military aircraft wore leather flaps over their ears, supposedly to protect against noise-induced hearing loss due to engine noise.

OSHA recommends the use of hearing protection devices (HPD) when an employer is exposed to an average noise intensity of 85 dBA over an 8-hour shift.

Some manufacturers combine headphones with ear defenders, allowing the wearer to listen to music, communication, or other audio source and also enjoy protection or isolation from ambient noise.

Earmuffs can be used in the workplace or recreationally for loud activities, e.g., concerts, shooting firearms, heavy machinery, mowing, etc.

[10] Exposure to loud noises damages the hair cells in the inner ear that are essential for sending neural impulses to the brain in order to perceive sounds.

[11] In the workplace, OSHA requires the use of hearing protection devices whenever a person is exposed to an average noise intensity of 90 dBA or greater over an 8-hour shift.

A typical earmuff attenuates (decreases) the level of noise by approximately 23 dB when tested under carefully controlled laboratory conditions.

[16] The EPA requires that earmuff manufacturers test each device's performance and indicate their specific noise-reduction capabilities on the product labeling.

Despite these drawbacks, research has shown that the real-world performance of earmuffs is in closer agreement to manufacturers' labels than it is for earplugs.

When deciding between earmuffs and earplugs, it is also important to consider the noise reduction levels achieved at different sound frequencies.

Earmuffs also fail to provide any noise reduction at infrasonic frequencies (< 20 Hz),[20] which is energy that cannot be heard because it falls below the range of human hearing sensitivity.

[21] Active earmuffs have an electronic component and microphones that allow the user to control their access to communication while attenuating background noise.

When in loud, hazardous settings, the wearer may still be required to listen to outside sources, such as machinery work, their supervisor's commands, or talk to their colleagues.

These earmuffs are designed to protect against a continuous signal, particularly low frequency sounds, such as diesel locomotives, heavy tractors, or airfields.

[16] At levels beyond this intensity, it becomes necessary for users to wear earplugs with earmuffs on top in order to achieve adequate protection from hearing damage.

[24] Dual protection is also recommended when shooting firearms because of the extremely high-level impulses (140 dB and greater) produced.

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.

[33] Technology in earmuffs is developing and shows promise in reducing the effects of airflow vibrations in the ear muffs.

[21] 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.

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.

Headbands may also lose their tension or ability to properly adjust to the head, which could lead to a decrease in device effectiveness.

[39] Workers that have sustained a standard threshold shift are required by OSHA to wear HPD at an 85 dB TWA.

Workers with a high frequency hearing loss may benefit more from HPD that attenuates sounds equally across the pitch range.

This is helpful because traditional HPD will attenuate the higher frequencies (where these individuals have a hearing loss) more than the mid- and low-frequencies.