Hearing

 Basic function of the ear

• The ear performs two distinct functions. It is used to detect sounds by receiving vibrations in the air, and  secondly, it is responsible for balancing and sensing acceleration. Of these, the listening aspect is more relevant to the maintenance engineer, and thus requires a basic understanding of how the ear works.
• As can be seen in the figure, the ear has three parts: outer ear, middle ear and inner ear. They receive vibrations from the air and convert these signals into nerve impulses that the brain can recognize as sound.

• Outer ear:The outer part of the ear directs sound to the auditory canal and eardrum. The sound waves cause the eardrum to vibrate.

•  Middle ears: Beyond the eardrum is the middle ear, which transmits vibrations from the eardrum through three small bones known as ossicles, to the inner ear fluid.The acoustic or aural reflex are two muscles in the middle ear that help protect the ear from sounds above 80 dB and reduce noise levels by up to 20 dB
  
  .This protection can only be provided for a maximum duration of 15 minutes, but cannot provide protection against sudden impulsive noises such as gunfire. This explains, why a person is temporarily 'deaf' for a few seconds after a sudden loud noise. The middle ear is usually filled with air, which is refreshing.The Eustachian tube, which connects this part of the ear to the back of the nose and mouth. However, this tube can allow mucus to pass to the middle ear, which can accumulate, interfering with normal hearing. 

• Inner ears

Unlike the middle ear, the inner ear is filled with fluid. The middle ear is attached to the cochlea in the last part of the ossicles. It consists of a fine membrane (basilar membrane) covered with hair-like cells that are sensitive to movement in the fluid. They detect any vibrations that cause nerve impulses to be transmitted to the brain. auditory nerve.

 Performance and Limitations of the Ear

The audible frequency range that a young person can hear is usually between 20 and 20,000 Hz (Hz), with the greatest sensitivity being around 3000 Hz.

The volume (or intensity) of sound is measured in decibels (dB). There are intensity levels for different sounds and activities.

Conversation  at 2 m ---50

Typewriter at  1 m-------65

Car  at 15 m    ---------70

Truck    at 15 m --------75

Power Mower  at 2 m --90

Propeller aircraft at 300 m---100

Jet aircraft  at 300 m-------- 110

Threshold of pain -----140

Hearing Protection

Noise levels can be reduced by up to 20 decibels using ear plugs and up to 40 decibels using earmuffs. However, using ear protection will adversely affect verbal communication. Despite this, it must be used consistently and as directed to be effective.