What is Normal Hearing?Mar 21, 2019
Have you ever wondered about hearing loss and what is considered “normal” hearing? You’re not alone. With so many people now living with a diagnosis of hearing, it’s no surprise that many wonder just what exactly “normal” is. Scientists determined the standard many years ago and with the help of many, many people.
How hearing works
Before we discuss how science determined normal levels of hearing, it’s important to understand just how your hearing works. It all starts with a sound that is captured by your outer ear. These sounds (sound waves) are funneled into your ear canal. From there, sound waves hit the eardrum. As they vibrate the eardrum, which is the beginning of the middle ear, the eardrum moves three small bones called ossicles to varying degrees depending on the pitch of the sound. It doesn’t end there, though.
As the ossicles move, signals are sent to the inner ear and the cochlea. The fluid within the cochlea begins to move, moving the hair-like cells within it. This minute movement is then translated to the brain as sound by way of the auditory nerve. In many cases, it is damage to the small hair-like structures of the inner ear, due to aging or exposure to loud noise, that result in hearing loss.
Hearing and hearing loss
As long as there have been humans there has been hearing loss. There is evidence of hearing loss in 10,000 year old skeletal remains from the Middle East, writings on the subject from Plato and Aristotle and the first electronic hearing aids were developed in 1940. It’s no wonder that science wanted to find common ground and global standards for hearing and hearing loss.
The core of that standard is “audiometric zero.” Audiometric zero is the frequency range detectable by someone with normal hearing. Generally, that range is from 0 dBHL (Decibel Hearing Level) to approximately 20 dBHL. It took a unique approach to determine this range, though. Researchers tested the hearing of thousands of attendees at the 1933 World’s Fair in Chicago. Once they were done, they determined an average for the lowest level those people could hear at certain frequencies. The resulting information became audiometric zero.
What does that mean?
Those with hearing loss are those who only hear louder sounds, those over 20 dBHL. They are unable to hear within the audiometric zero range.
Individuals can have varying degrees of hearing loss as determined by a hearing evaluation:
- Hearing loss of 20 to 40 decibels=mild hearing loss
- Hearing loss of 41 to 60 decibels=moderate hearing loss
- Hearing loss of 61 to 80 decibels=severe hearing loss
- Hearing loss of more than 81 decibels=profound hearing loss
Any loss over 40 decibels is considered a hearing impairment.
To give you a better idea of what these decibel levels mean, here are some common sounds and where they measure in decibels:
Quiet countryside: 20 dB
Conversation: 60 dB
Traffic: 80 dB
Jet engine: 140 dB
Sustained exposure to noises over 90 dB can lead to hearing loss.
Our hearing is delicate and easily damaged. It is important to protect it with hearing protection and regular hearing evaluations. These screenings can help determine if you have a hearing loss and how best to manage it to protect further loss.