What Does It Mean to Have “Normal” Hearing?
In audiology, we hear a lot about “normal” hearing, but we don’t often talk about what it is. We assume that “normal” is a kind of pure state of full hearing ability, but how do we know what that is? Who is it for? For example, if the average 30-year-old has a significant degree of hearing loss compared to the average 18-year-old, does that mean all 30-year-olds have hearing loss? Or should there be a different “normal” range of hearing for a 30-year-old? Or, yet, does it indicate that there is an epidemic of hearing loss in our population caused by excessive exposure to noise and/or chemicals, causing hearing loss in nearly everyone?*
The definition of “normal” hearing is, indeed, the absence of hearing loss, but there is a somewhat complicated process by which this has been established, and by which it is measured in individuals.
Audiometric Zero
The absence of hearing loss is determined by a concept known as “audiometric zero.” Audiometric zero is determined on the basis of individual frequencies (or pitches, like we used to talk about musical notes), where “zero” is defined as the minimum average level that people can hear at a given frequency. Audiometric zero for each common frequency was determined by hearing tests conducted at the 1933 World’s Fair.
Pure Tones
A “pure tone” is represented as a sine wave. If you pluck a string on a guitar or a violin, or play a note on a clarinet or flute, or sing a note, you hear much more than just the note itself. All of the extra information around the note is what is called “timbre,” and helps your brain determine what instrument (or person) you’re hearing. A pure tone is, simply, a tone that has no sonic information outside of a single frequency. Pure tones are achieved with implements like tuning forks or electrical signal generators. By using pure tones, audiologists can measure a person’s hearing ability at a single frequency.
Audiometric Zero and “Normal” Hearing
Audiometric zero is represented as 0 dBHL (Decibel Hearing Level). While a person with excellent hearing would be able to hear 0 dBHL at any frequency, “normal” is actually defined as anywhere between 0 and 20 dBHL at a given frequency. So, it is possible to lose 20 dBHL of hearing ability and still be considered to have “normal” hearing.
This is why it is so important to get your hearing tested regularly. Even people who don’t notice any hearing loss may be losing their hearing to a cause that could be modified. Excessive exposure to noise, cigarette smoking, and exposure to certain pharmaceuticals or other chemicals all may cause hearing loss. By getting your hearing tested regularly, you can catch hearing loss before it becomes a problem and try to remove the causes of hearing loss from your routines. This might involve quitting smoking, wearing hearing protection on the job or when engaging in noisy activities, or changing medications.
The Better Hearing Institute, a non-profit organization, recommends getting a hearing test once every decade until age 50, and once every 3 years after that. Those with a higher risk for hearing loss, or who already have hearing loss outside the normal range, should be tested more regularly.
The Range of Hearing Loss
Outside the range of normal hearing (0–20 dBHL), the range of hearing loss can be considered to progress in 20-dBHL increments, as follows:
- Mild hearing loss – 20–40 dBHL
- Moderate hearing loss – 40–60 dBHL
- Severe hearing loss – 60–80 dBHL
- Profound hearing loss – 80–100 dBHL
- Deafness – +100 dBHL
It is possible to measure what is considered “normal” hearing at a variety of age groups, and this has been done. A “normal”-hearing 80-year-old person, for example, has what would be considered moderate-to-severe hearing loss above about 3000 Hz.
While we don’t yet know why so many people experience hearing loss as we age, we do know that hearing aids can help to mitigate the effects. Those who get hearing aids overwhelmingly report that they’re happy with them (when asked after one year), and there is ample evidence to indicate that hearing aids help us stay more active, healthier, and happier even as our hearing issues may worsen. If you or a loved one is experiencing hearing loss, make an appointment for a hearing test today and find out what hearing aids can do to improve your life!
*In fact, it is estimated that about 20% of teenagers have measurable hearing loss in one or both ears.
