About Hearing

​​​​​​​Parents who are told that their child is deaf or hard of hearing can display a wide range of emotions and reactions. One of the first steps in understanding hearing loss is to understand how we hear, the types of hearing loss, and what we hear. It is also helpful to explore how hearing changes and milestones to watch for as children grow.​

Note: This page includes contributions from both the babyhearing.org team and a team that originally created a site for families focused on 'raising deaf kids' (see About Us​).​

How the Ear Works


How We Hear

Sounds are all around us.

We hear when these sounds pass through the outer, middle and inner parts of our ears, sending thousands of tiny vibrations up to our brain for interpretation.

First sound travels through the outer ear canal and makes the eardrum move. When the eardrum moves, the three middle ear bones vibrate. This vibration creates movement of fluid in the inner ear also known as the cochlea.

The fluid movement causes sensory receptors in the coiled shaped cochlea, to send a signal along the auditory nerve to the brain—and this is how we hear.

  • Outer Ear: Sound waves travel through the ear canal and make the eardrum move.
  • Middle Ear: When the eardrum moves, the ossicles (middle ear bones) vibrate. This vibration creates movement of fluid in the inner ear.
  • Inner Ear: The movement of fluid causes special cells in the inner ear to send nerve signals to the brain. Once the brain receives the message, it identifies that message as sound.

Types of Hearing Loss

Hearing loss may be located in the outer, middle and/or inner ear. There are 3 types of hearing loss:

Conductive Hearing Loss

Conductive hearing loss is caused by a problem in the outer or middle ear resulting in sound being unable to travel to the inner ear properly. Many instances of conductive hearing loss can be treated with medicine or surgery. Causes of conductive hearing loss can include wax in the ear canal, fluid in the middle ear or a hole in the eardrum.

Sensorineural Hearing Loss

Sensorineural hearing loss is caused by a problem in the inner ear. Sensorineural hearing loss usually cannot be cured with medicine or surgery, but hearing aids or cochlear implants can help in most cases. In young children, sensorineural hearing loss can occur due to:

  • Certain infections before birth
  • Lack of oxygen during birth
  • Genetic causes

Mixed Hearing Loss

Mixed hearing loss is a combination of conductive and sensorineural hearing loss. An example of mixed hearing loss is when children with sensorineural hearing loss also have middle ear problems (such as fluid in the middle ear). This can make hearing loss worse.

Unilateral Hearing Loss

Unilateral hearing loss is when hearing loss is only in 1 ear.

Progressive Hearing Loss

Progressive hearing loss is when the hearing loss gets worse over time.

Fluctuating Hearing Loss

Fluctuating hearing loss is when the hearing loss changes. It may sometimes be worse and sometimes better.

The Sounds We Hear​​

Facts about sound 

  • Sound travels through the air as waves you can't see.
  • The faster the waves are, the higher the sound.
  • How fast a sound travels is called its frequency. Frequency describes how high or low a sound's pitch is.
    • High-pitched sounds (like a squeal) have a higher frequency.
    • Low-pitched sounds (like thunder) have a lower frequency.
  • Frequency is measured in hertz (Hz).
  • The bigger the sound waves, the louder the sound.
  • The loudness of sound is measured in decibels (dB).

What we typically hear

People with hearing in the average range can hear from about 0 dB to 140 dB. Here's how loud those sounds can be:​

Sound Loudness, in dB
​​whisperabout 20 dB
refrigerator hummingabout 40 dB
normal conversationabout 60 dB
noise of traffic in the cityabout 80 dB
lawn mowerabout 90 dB
chainsawabout 110 dB
firecrackerabout 140 dB


People with hearing in the average range can hear sounds as low as 20 Hz. Some can hear as high as 20,000 Hz. Here's how high or low those sounds can be:​

Sound High or low sounds, in Hz
thunder20 Hz to 80 Hz
talking250 Hz to 6,000 Hz
opera singer hitting a high note2,000 Hz

Interact with the Listen Up! infographic below to hear how noisy different sounds are in our environment:

How Our Hearing Changes As We Grow

Read this section to learn how hearing changes as children grow.

The timelines below show the ages at which most hearing babies have developed these skills.
Just remember, all children are different. They may not do all of these things on time. If you think your child has a hearing loss, talk to your doctor.

Hearing Changes with Growth

Your child can hear things even before she's born.

A child's hearing changes a lot until 4 to 8 years old.
Based on the typical growth for the following age ranges, your child may:

From birth to 3 months:

  • React to loud noises.
  • Wake up at loud sounds.
  • Be soothed by the sound of your voice.
  • Start making sounds in the back of her throat, like "goo."

From 3 to 6 months:

  • React to the sound of your voice.
  • Start turning her head or eyes towards sounds.
  • Like playing with toys that make noise.
  • Stop to listen to voices.
  • Smile when someone talks to her.
  • Cry in different ways when she needs different things - such as if she's hungry or needs to be changed.

From 6 to 12 months:

  • Answer to her name.
  • Make many different baby-talk sounds.
  • Start to understand simple words, like "mama," "dada," and "wave bye-bye."
  • Turn her head to familiar sounds, like a telephone ringing.
  • React to changes in your tone of voice.

By 12 months:

  • Copy sounds that she hears.
  • Answer simple questions like, "Where's the ball?"
  • Recognize her name.
  • Understand what "no" means.

From 12 to 18 months:

  • Give you a toy when you ask her.
  • Point to parts of the body when you ask her.
  • Put sounds together.
  • Use a few simple words, like "mama," "more," and "no."
  • Follow simple directions that you tell her.

By 18 months:

  • Understand about 50 words..

By 2 years:

  • Understand yes and no questions.
  • Use words that you often use at home or school.
  • Make simple sentences.
  • Follow simple orders without being shown what to do.

By 2 ½ years:

  • Use about 270 words.
  • Say or sing short rhymes and songs.
  • Check out interesting sounds, or tell others about them.

By 3 years:

  • Make simple sentences of 3 to 4 words.
  • Use about 1,000 words.
  • Be able to tell a simple story.
  • Know her name and the names of people in her family.
  • Sing songs.

To learn more about how your baby's speech, language, and hearing changes with age, visit the links below to find useful handouts from www.boystownresearchhospital.org. 

If you have concerns that your child is not meeting these milestones, talk to your child's physician about scheduling a hearing evaluation with a pediatric audiologist.​