How We Hear

To understand hearing loss, it helps to know the basic mechanics of how we hear.

Woman holds her hand near ear and listens carefully

When working properly, ears are sophisticated organs capable of processing sounds from the scarcely audible to extremely loud. Ears can assess volume and how close or far away sounds are, and identify from where sounds originate, with a great deal of accuracy.

Before we break down the sections and parts of the ear, it is important to note that hearing happens mostly in the brain. Sound is a physical disturbance in the air that can be measured objectively, and what you hear is your brain’s interpretation of that vibration. This means that while a particular sound may have universal properties, how it is perceived and experienced will differ for everyone. The following explains how this complex process works.

What are decibels?

Like the proverbial tree that falls in the forest, sound has existed for longer than organisms were around to hear it. The ear is essentially a filter for these airborne vibrations that are translated in the brain, producing the sensation known as hearing. Although sound may seem less tangible than texture or color, it is actually a physical phenomenon that can be measured and observed visually through various imaging processes. The degree of a sound’s loudness is measured using units called decibels (dB). Decibels are measured from zero, the threshold of human hearing, to 130, the threshold of pain. For example, a quiet bedroom would register at about 30 dB, while fireworks and close artillery can exceed 120 dB and cause significant damage.

The ear becomes damaged if overexposed to excessive noise. While the most common cause of hearing loss is regular exposure to loud noise over time, often due to prolonged use of heavy machinery on the job, even one-time exposure to an extremely loud sound like a gunshot can lead to auditory problems. The physical intensity of these sounds can permanently rupture sensitive regions of the ear and bend or break the irreplaceable hair cells that send sound impulses to the brain. This is called noise-induced hearing loss (NIHL) and it may or may not be accompanied by tinnitus (hearing a ringing, buzzing, or similar noise without an external source). Unlike other forms of hearing loss, NIHL can be prevented if you learn to recognize the risks and take reasonable precautions.

If you believe you are at high risk of exposure to 85 dB or greater, please review our tips for avoiding hearing loss.

How many decibels are too many?

Decibels are measured in multiples of sound intensity. For example, if a noise increases by 10 on the decibel scale it has grown 10 times more powerful. At lower volumes, this change is subtle but it can become dangerous rather quickly in the higher ranges.

Though most sounds you encounter in your everyday life are well below the danger level, such as office conversation or white noise from a humming air conditioner (both about 60 dB), noises that are 85 dB or higher put your hearing at risk. Examples of sounds that exceed this range include:

  • Motorcycles
  • Gunfire
  • Fireworks
  • Subways
  • Airplanes
  • Jackhammers

The following chart demonstrates the decibel level of everyday sounds, though the exact numbers can vary based on proximity and intensity of exposure. Note that while the threshold for pain begins at around 125 dB, the Occupational Safety and Health Administration indicates that long-term exposure to levels higher than 85 dB could result in hearing loss even when no discomfort is felt in the ear.

dbchart

The general rule is that the louder the sound to which you are exposed, the less time it will take for hearing loss to occur. Follow this simple advice:

If the noise is too loud, too close, and lasts too long—avoid it!

Does your job put you at high risk of hearing loss?

Some professions put you at greater risk of hearing loss than others, due to regular exposure to excessive noise. These include:

  • Public service (e.g., firefighting, ambulance driving)
  • Construction work
  • Military service
  • Industry and factory work
  • Music and entertainment
  • Farming

Recreational activities may also damage your hearing if you do not take proper care to protect your ears. Examples of risky activities include the following:

  • Hunting
  • Attending concerts or dance clubs
  • Setting devices above 70% volume while wearing earbuds
ear plugs

The Ear

Now that you are more familiar with sound and volume, let’s look at the parts of the ear and their various functions. The human ear is constructed of three sections—the outer ear, the middle ear, and the inner ear.

Ear-graphic_en_596px

The outer ear is the visible part, also called the pinna or auricle. It consists of skin and cartilage with muscles attached to the back. The pinna’s primary function is to collect and direct sounds down the ear canal. Constructed of twists and folds that enhance high-frequency sounds and help determine the direction of the sound source, sounds coming from the front and to your side are slightly enhanced as they are directed into the ear canal, while sounds from behind you are somewhat less pronounced. This helps you hear what is most directly in front of you while reducing distracting background noise. If your pinna is functioning normally, it is providing about 5 dB of high-frequency enhancement to your hearing, as well.

The ear canal is also part of the outer ear. This S-shaped passage is approximately one inch in length, and roughly the diameter of a pencil eraser. The resonant tubes of the ear canal increase gain (amplification) by 15–25 dB as sound is conducted toward the middle ear. The inner portion is encased by bone, while the outer portion of the ear canal is surrounded by cartilage and contains glands that produce cerumen (or earwax). Although some people regularly clean their ears to remove this wax, you should really leave it alone. Earwax actually protects your skin and tympanic membrane from drying out while keeping unhealthy bacteria from multiplying. It also forms a barrier against foreign bodies, such as dust and insects. For these reasons, as well as to avoid perforating your eardrums, hearing care professionals highly discourage using cotton swabs and other objects to remove earwax. If you have a problem with excessive earwax production, you should see a professional for advice, and if deemed necessary, removal..

The tympanic membrane (or eardrum) separates your middle ear from the outer ear. Directly behind the eardrum is a row of three tiny bones collectively known as the ossicles. These consist of the following:

  • Malleus (the hammer)
  • Incus (the anvil)
  • Stapes (the stirrup)

The ossicles vibrate in response to eardrum stimulation, amplifying and relaying sound to the inner ear through an oval window. They also boost the sound’s gain by an additional 27 dB.

The opening to the Eustachian tube ventilates your middle ear and connects it to the back of your throat. This tube also opens when you swallow, yawn, blow your nose, or cough.

Your inner ear, which is shaped like a snail’s shell, is divided into two functionally separate sections: the vestibular, or balance organ, and the cochlea, or hearing organ. The cochlea conducts high frequencies at its base and low frequencies at its apex. Because the sound wave always passes through the base first, early hearing loss usually occurs at the higher frequencies.

The sound wave causes the fluid in the inner ear to move, stimulating rows of thousands of tiny hair cells (stereocilia, or hearing nerve cells) inside the cochlea for each particular frequency. These hairs, which allow you to register a sound’s loudness among other functions, release neurotransmitters via the auditory nerve to the brain, which interprets them as sounds. These hair cells are delicate and can be damaged or destroyed due to overexposure to loud noise, genetic predisposition, or the aging process. Once you lose a hair cell, it cannot be replaced with today’s technology. The more of these you lose, the less hearing you retain.

Binaural Hearing

Another amazing property of hearing is that it is binaural, which literally means “used with both ears.” Like a set of stereo speakers, ears automatically communicate with each other to determine the direction of sound. What you hear is not two independent streams of sound from the left and right, but a full spectrum all around you. Eyes coordinate similarly to give your vision a full sense of depth. Many of today’s hearing aids feature binaural functionality, allowing users to experience the subtle spatial elements of sound that can be erased if improperly amplified. For more information on how hearing aids adjust and deliver sound to your brain, see our guide to hearing aid benefits and features.

Though related to hearing, tinnitus is frequently caused by a malfunction in the brain’s perception of sound, not the ear. Our page on tinnitus provides a detailed look at this condition, as well as possible causes and treatments.

Preserve the gift of hearing

As you can see, the ear is one of the most complicated and important parts of our sensory system. Even if you don’t think you have hearing loss, it is important to remain vigilant when it comes to protecting your ears from damage at home and at work. Our website is filled with links to the best ways to prevent and treat hearing loss. While it is helpful to be informed, only a hearing care professional has the tools necessary to diagnose and correct hearing loss. Schedule an appointment today to have your hearing tested and determine if action needs to be taken so that you can continue enjoying your favorite sounds for years to come.