Hearing Screening E-Learning Course

Hearing Screening E-Learning Course

Normal Hearing and Hearing Loss

Normal Hearing

Two characteristics of sound: frequency (hertz) and volume (decibels) are measured by pure tone audiometry.

Frequency (pitch or tone) is the range of sound pitch, measured in Hertz (Hz). One Hertz is the equal to one sound wave or cycle per second. The more frequent the sound waves, the higher the pitch, and the higher the Hertz number. Although we can hear sounds as quiet as 20 Hz, we use a limited range of frequencies (250 Hz through 8000 Hz) for our daily listening needs. This frequency range is critical for hearing and understanding speech and other sounds, and is the reason routine hearing screening uses 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, and 6000 Hz (ages 11 and older).

Volume (intensity or loudness) is the range of sound loudness measured in decibels (dB). The greater the decibel number, the louder the sound. The minimal sound level that the majority of people with normal hearing can detect is 0dB. At least twenty percent of children can hear sounds as quiet as -10dB (Roberts & Huber, 1967). People usually speak at an intensity of 45-60dB (CDC, June 2012). A 130dB sound causes pain in most people’s ears.

A person with normal hearing should be able to hear volumes as quiet as -10dB to 14dB and frequencies of 250 through 8000 Hz.

Examples of different sound and volumes as expressed in dB

dB Common Sounds
10 to 0 dB Softest sounds most people can hear
30 dB Very soft whisper
60 dB Ordinary conversation
80 dB Loud radio
90 dB City traffic or a person's shout
110 dB Loud thunder
120 dB Rock band
140 dB Jet engine take-off
180 dB Rocket at take-off

While decibels greater than or equal to 120 to 130 dB cause pain or discomfort in most people’s ears, some people will experience pain at sounds of 100-110 dB.

Hearing Loss

Hearing loss is when the quietest or lowest decibel someone can hear (16dB or more) is louder than the sound someone with normal hearing can hear (0-15dB). The American Speech-Language- Hearing Association (ASHA) (2010) classifies hearing loss based on the lowest decibel at which someone can hear a sound, as follows:

dB Hearing loss
0-20 dB Normal hearing
21-25 dB Slight hearing loss
26-40 dB Mild
41-55 dB Moderate
56-70 dB Moderately severe
71-90 dB Severe
91+ dB profound

Types of hearing loss

Hearing loss is either conductive or sensorineural, and depending upon the anatomical location of the loss, can be in the external, middle, or inner ear.

Conductive Hearing Loss

  • Occurs in the outer and/or middle ear.
  • Blocks movement of sound to the inner ear.
  • Typical causes are wax in the ear canal, hole in the eardrum, broken ossicles (middle ear bones), middle ear fluid or infection.
  • Usually can be treated medically or surgically; use of amplification devices such as hearing aids can help.

Sensorineural Hearing Loss

  • A sensorineural problem in the inner ear, auditory nerve, or brain.
  • It is the most common type of permanent hearing impairment.
  • Typical causes are genetics or damage to sensory nerves due to ototoxic drugs, infections trauma, or noise.
  • Treatment may include use of amplification devices such as hearing aids or cochlear implants

Combined Hearing Loss

  • Involves both conductive and sensorineural hearing loss.

Prevalence of hearing loss

Hearing loss is one of the most common birth defects. Approximately 1.6 per 1000 infants screened are born with hearing loss (CDC, 2014 (PDF)).

  • In Minnesota, 259 babies were born in 2014 with hearing loss (Minnesota Early Hearing Detection and Intervention, 2014).
  • In 2015, 2,168 children in Minnesota ages 3 -5 years were identified as having new potential problems with hearing through Early Childhood Screening (Minnesota Department of Education, 2015).
  • Six out of 1000 children have permanent hearing loss by age six (Choo & Meinzen-Derr, 2010).
  • Approximately 30 to 50 per 1000 children have hearing loss by adolescence (American Academy of Audiology [AAA, 2011])

Causes of hearing loss

  • At least half of congenital hearing loss is associated with genetic risk factors (Kaye, 2006).
  • Environmental infections or toxins are another common cause of infant and childhood hearing loss. Infections that can cause hearing loss include toxoplasmosis, cytomegalovirus, and otitis media. Ototoxic drugs that can cause hearing loss in infants and children include aminoglycosides and cisplatin. A large percentage of permanent childhood hearing impairment does not have a known cause (Korver et al., 2011).
  • Children also acquire hearing loss due to noise exposure.

Noise exposure and hearing loss

There are 15,000 to 20,000 tiny cells (cilia) in the inner ear that send sounds to the brain. When these cilia are damaged, hearing loss can result. As an illustration of what happens when these cells have been exposed to too much noise, think about when you walk on fresh grass. When you walk on it lightly only a few times, it bounces back to its original shape. However, if you walk on the grass often enough or if you trample it, it becomes matted down and will not bounce back. Exposure to sounds that are loud enough or occur for long enough can damage the ears’ tiny cells so that they can no longer bounce back into shape and can no longer send sound to the brain. This causes noise-induced hearing loss (NIHL), which is a type of sensorineural hearing loss.

NIHL can be temporary or permanent; it can result instantly from a single loud noise like a firecracker or gunshot, or can occur gradually from repeated exposure to noise. Approximately 12.5 percent (5.2 million) of children 6 to 19 years of age have some level of noise-induced hearing loss (CDC, 2011b).

You may download more information on Noise Induced Hearing Loss in a pdf format.


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