“A decibel is a measure of 1/10 of a bel, using a logarithmic scale, meaning it is a way to express very large numbers in a convenient way. Decibel originates from efforts to quantify telegraph and telephone circuits in the early 20th Century to express these very large ratios.
The point is that the human perception of the intensity of sound is not linear. Something that is perceived as louder, may actually be extremely loud. This is known as the Weber-Fechner law which applies to all of our senses. It states that the minimum increase of sound will produce a perceptible increase of sound that is proportional to the pre-existent stimulus.” - Drew Sutton, MD, Board-Certified Otolaryngologist
Many people take the sense of sound for granted, but when you really sit down and think about it, an immense amount of complexity goes into sensing and perceiving sound.
Sound at its most fundamental level is a series of pressure waves caused by the compression of air. When something makes a noise, it can be thought of as a water drop hitting a still pond and emanating outwards in all directions. When a sound is created, it acts as the drop of water, and the subsequent sound created can be thought of as the ripples in the water.
The ears take the external stimulus of the changes in pressure and convey that into neurological impulses that are then interpreted by the brain. While the ears are excellent at discerning the differences between sounds, it is not without its shortcomings. One of those occurs with loud noise exposure.
Loudness, which is measured in decibels (dB), is an exponential measurement and is a great tool utilized to quantify the intensity of sounds. Loud sound exposure can cause long-term and even permanent hearing loss. This represents why it is essential to understand the ear’s threshold for loudness and try to stay within that limit as much as possible.
Below is a detailed look at the components of sound, how decibels are measured, the dB threshold for your ears, as well as ways you can help with noise-induced hearing loss.
Components of Sound
A sound is a form of energy that is transmitted through a medium. In the case of the sound we hear, that medium is air, but this isn’t the only way sounds can be transmitted. If you have ever been underwater, you have likely still heard sounds, and this is because, just like air, water is a medium that sound energy can travel.
Sound has many different properties, and these include frequency, waveform, and amplitude. These three properties give each sound its uniqueness, and the body utilizes differences in each of these properties to perceive different sounds.
The term frequency refers to the number of wavelengths that occur in a given unit of time. With sound, a wavelength consists of one compression and one rarefaction of a sound wave. Frequency is measured in hertz, which is the number of wavelengths per one second. The human ear can perceive sound anywhere from 20 hertz to 20,000 hertz.
Frequency, better known as the pitch, allows for the many perceivable pitches that you experience. The higher the pitch is, the more hertz that sound wave will carry.
The waveform is a property that looks at the unique sound signatures found in nature. Many sounds will vary in frequency and intensity as it is happening and give them their unique properties.
A great example is musical instruments. You can play the same pitch on different instruments, but they will have their unique properties. This is known as timbre and is an essential aspect of sound identification. For instance, people’s voices have a timbre unique to something else with the same frequency and intensity.
Amplitude, also referred to as intensity, is a property that looks at how much energy a sound wave carries. For sound, this equates to the amount of maximum pressure reached during the compression phase of the wave.
Intensity is of great importance for hearing health because the intensity of sound can damage your hearing. The louder a sound, the higher the amplitude, while the softer the sound, the lower the amplitude.
What Is a Decibel?
A decibel is a unit of measure for the intensity of sound. Unlike other units of measure, the decibel scale is on a logarithmic scale, and for every 10dB increase, the sound pressure level will have a 10-time increase.
Decibels are a quantifiable way of looking at the volume level of a sound. This is important in many regards, and one of the most important is understanding what environments could harm an individual’s hearing. Several jobs require being in environments with loud sounds, and the use of a decibel meter allows both employees and employers to ensure everyone’s hearing safety.
Decibel Level and Hearing Loss
Hearing loss is something that occurs to a large handful of individuals. Some people may be born with hearing loss, while others may develop it throughout their life. There are many possible factors into hearing loss, but one significant indicator of developing hearing loss later in life is frequently being exposed to loud sounds for extended periods.
Decibels allow for a quick and easy determination of noise levels, and by knowing what noise levels are considered safe, you can ensure that you protect your hearing for the long run. Below is a closer look at how decibels relate to hearing loss.
Unsafe Decibel Ranges
According to the CDC, decibel levels over 70dB can be of concern and trying to maintain a noise level below 70 dB is ideal for your hearing health. While this is best practice, it certainly isn’t always possible, and that is fine as long as you are mindful of how long you are being exposed to a particular noise.
As a general rule, the higher the dB over 70 dB, the less time you should be exposed to it. An example would be that you could be next to a lawnmower for two hours before potentially causing hearing damage, while for something like headphones cranked up all the way, damage can set in at as little as five minutes into listening.
Below is a breakdown of the loud decibel ranges and how long you can be exposed before the possibility of causing hearing loss.75dB - 8 hours
85dB - 2 hours
95dB - 50 minutes
105dB - 5 minutes
>120dB - Possibility for hearing loss for any amount of time
How Do Loud Sounds Lead To Hearing Loss?
It is generally easy to remember that below 70dB is safe for your hearing health, but understanding the underlying reason as to why it contributes to hearing loss can make it easier to remember.
The first thing to understand is how the ear can hear sound. The ear is composed of three sections which are the outer, middle, and inner ear. Sound travels from the outer ear into the inner ear in a unique fashion.
Sound enters the ear canal, where it meets a dead end known as the eardrum. With the pressure of sound waves, the eardrum is displaced and vibrates. The vibration of the eardrum is what then causes the movements of the bones within the inner ear. These bones then translate the vibration to the auditory organ known as the cochlea, also considered the inner ear.
The cochlea has thousands of sensory hairs within it. When the sound is translated to the cochlea, it sends an internal shock wave through the cochlea. Each hair within the cochlea is finely tuned to detect a certain pitch of the sound, and when that hair matches the shock wave, the hair bends and initiates a nerve pulse that is then sent to the brain.
Sustained exposure to loud noises can induce hearing loss in the inner ear, also referred to as sensorineural hearing loss. This damage is caused by placing strain on the hair receptors within the cochlea. When the hairs are overused for an extended period, it can damage them and reduce auditory acuity.
Another less common way that loud sounds can cause hearing loss is by causing your eardrum to rupture, also known as an eardrum rupture. If a sound is loud enough and applies enough pressure to your eardrum, the eardrum can give way and cause a hole in the thin membrane. With a hole in the membrane, it can’t vibrate as well since some pressure escapes into the middle ear.
While this circumstance is possible, it is highly unlikely and only likely if you are very close to an explosion or gunshot without hearing protection.
Some other examples of loud sounds that may cause some degree of hearing loss include garbage disposal, motorcycle, diesel truck, helicopter, jackhammer, a jet take-off, food blender, loud outdoor noise, alarm clocks, propeller plane flyover or jet flyover, thunderclap (chainsaw), fireworks, power mower, garbage truck, air conditioning unit, shouted conversation, farm tractor, washing machine heavy traffic (city traffic), rock concerts, and newspaper press.
On the other hand, some not harmful sounds to your hearing include normal breathing, bird calls, quiet library environments, refrigerator, or refrigerator hum.
In summary, hearing health is something that you need to take care of throughout your life. Listening to your headphones on full blast, frequently going to concerts without any hearing protection, and more can contribute to hearing loss.
Decibel ranges over 70dB can cause lasting damage within the inner ear, with louder sounds able to cause damage faster. If you have experienced a diminished sense of hearing due to loud noise, it may be helpful to get a hearing test with an audiologist and work towards getting your hearing back.
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