How you hear

  • Outer ear collects sound waves, sends them through ear canal to ear drum (tympanic membrane) that starts to vibrate.

  • Membrane is attached to three tiny bones- hammer (malleus), anvil (incus), stirrup (stapes) - that pass vibrations to cochlea in inner ear.

  • Inner ear is filled with thin fluid that transmits pressure changes throughout the cochlea.

  • Tiny hair cells inside the cochlea pick up sound vibrations from the fluid and send thousands of electrical impulses up auditory nerve to the brain.

  • These electrical signals are then interpreted as sound.

  • Overexposure to sound cause the hair cells to become overstimulated, fatigued and stop responding to sound - leading to Noise Induced Hearing Loss (NIHL).

Sound Pressure Level, dBA,  Sound Dose, Safe Listening

A sound wave is a longitudinal wave that propagates by displacing differences in force or pressure from one place to another. 

Sound Pressure Level is logarithmic (nonlinear) and is generally expressed in decibels measured using A-weighting network - hence dBA.

Sound Dose is the total dBA received during a specified period e.g.daily, weekly.

Safe listening refers behaviors to lower individual’s NIHL risk

Duration of safe listening time has a nonlinear relationship with dBA 

Depends on the level (loudness), duration (time period) and frequency of exposure through audio or ambient sources.

For example 

Weekly safe listen time decreases from 40 hrs at 80 dBA to 10 hrs at 86 dBA to 75 mins at 95 dBA to 4.5 mins at 107 dBA

Safe Listening Times for Everyday Sounds and can be very Different




Normal talk



Lawn mower




Movie Theater


Sporting Events






Jet taking off

You can protect your hearing 

Reduce listen time

Take listen breaks

Choose safe listen activities after a loud exposure (e.g concert); ears need ~ 18hr to return to normal hearing

Increase distance from sound source

Wear appropriate Hearing Protection Device

dB (Safe Listen mins)


70 (1440)





80-85 (480)

90-110 (120-10)





110-129 (2)

130-140 (1)

140-160 (0)

References: World Health Organization, US Centers for Disease Control and Prevention, US National Institutes of Health (National Institute of Deafness and other Communication Disorders), US Environmental Protection Agency