“A decibel corresponds to one-tenth of a bel, expressed on a logarithmic scale: it is therefore a convenient way of representing very large numbers. The decibel was born from work carried out in the early 20th century to quantify telegraphic and telephonic circuits and to express these very high ratios.
What you need to remember is that human perception of sound intensity is not linear. A sound perceived as slightly louder can in reality be extremely powerful. This is what the Weber-Fechner law states, which applies to all our senses: the minimal increase in a sound necessary to produce a perceptible rise is proportional to the stimulus already present.” - Drew Sutton, MD, board-certified otolaryngologist
Many people take hearing for granted, but when you take the time to think about it, considerable complexity is involved in the detection and perception of sounds.
At the most fundamental level, sound is a series of pressure waves caused by the compression of air. When an object makes a noise, you can imagine it like a drop of water falling into a still pond and spreading in all directions. The noise emitted acts as the water droplet, and the resulting sound as the ripples on the surface.
The ears capture the external stimulus that these pressure variations constitute and convert them into nerve impulses, which are then interpreted by the brain. While the ear excels at distinguishing sounds from one another, it is not without its limits. One of these appears during exposure to loud noises.
Sound intensity, measured in decibels (dB), follows an exponential progression and is an excellent tool for quantifying the power of sounds. Exposure to loud sounds can cause lasting, or even permanent, hearing loss. Hence the importance of knowing the ear's tolerance threshold and staying below this limit as much as possible.
Below you will find a detailed review of the components of sound, how decibels are measured, the dB threshold your ears can withstand, as well as solutions for hearing loss due to noise.
The components of sound
Sound is a form of energy transmitted through a medium. In the case of the sounds we hear, this medium is air, but it is not the only possible medium. If you have ever been underwater, you have undoubtedly continued to hear sounds: like air, water is a medium in which sound energy propagates.
Sound has many properties, including frequency, waveform, and amplitude. These three properties give each sound its unique character, and the body relies on their differences to perceive distinct sounds.
Frequency
The term frequency refers to the number of wavelengths that occur in a given unit of time. For sound, one wavelength corresponds to a compression and a rarefaction of the sound wave. Frequency is measured in hertz, which is the number of wavelengths per second. The human ear perceives sounds from 20 hertz to 20,000 hertz.
Frequency, better known as pitch, is at the origin of the multitude of pitches you perceive. The higher a sound is, the more hertz the sound wave contains.
Waveform
Waveform is the property that looks at the unique sound signatures found in nature. Many sounds vary in frequency and intensity during their emission, which gives them their own characteristics.
Musical instruments are an excellent example of this. You can play the same note on different instruments: each will have its own characteristics. This is called timbre, an essential element of identifying sounds. Thus, each person's voice possesses a timbre that distinguishes it from any other sound of the same frequency and intensity.
Amplitude
Amplitude, also called intensity, is the property that describes the amount of energy carried by a sound wave. For sound, it corresponds to the maximum pressure reached during the compression phase of the wave.
Intensity is of great importance for hearing health, because an intense sound can damage your hearing. The louder a sound is, the higher the amplitude; the weaker it is, the lower the amplitude.
What is a decibel?
The decibel is a unit of measurement for sound intensity. Unlike other units, the decibel scale is logarithmic: each 10 dB increase corresponds to a 10-fold multiplication of the sound pressure level.
Decibels offer a quantifiable way to understand the volume of a sound. This is important in many respects, particularly for identifying environments that could be harmful to hearing. Many jobs require working in noisy environments, and the use of a sound level meter allows both employees and employers to ensure everyone's hearing safety.
Sound level and hearing loss
Hearing loss affects a very large number of people. Some are born with it, others develop it over the course of their lives. There are many possible factors, but one of the main warning signs of future hearing loss is frequent and prolonged exposure to loud sounds.
Decibels allow for a quick and simple assessment of sound levels: by knowing which levels are considered safe, you can protect your hearing in the long term. Here is a closer look at the link between decibels and hearing loss.
Decibel ranges at risk
According to the CDC, sound levels above 70 dB can be problematic: staying below 70 dB is ideal for the health of your hearing. That is the golden rule, but it is obviously not always possible — and that's okay, provided you remain attentive to the duration of your exposure to a given noise.
As a general rule, the more the level exceeds 70 dB, the less time you should be exposed to it. For example, you can stay next to a lawnmower for two hours before risking damage to your hearing, whereas with headphones turned up to the max, damage can appear after just five minutes.
Here is the breakdown of high decibel ranges and the possible exposure time before any risk of hearing loss.
75dB - 8 hours85dB - 2 hours95dB - 50 minutes105dB - 5 minutes>120dB - Risk of hearing loss regardless of duration
How do loud sounds cause hearing loss?
It is fairly easy to remember that below 70 dB your hearing is not at risk, but understanding why loud sounds promote hearing loss helps to remember it.
The first thing to understand is how the ear perceives sound. The ear consists of three parts: the outer ear, the middle ear, and the inner ear. Sound travels from the outer ear to the inner ear in a very specific way.
Sound enters the ear canal, where it encounters a dead end: the eardrum. Under the pressure of sound waves, the eardrum moves and vibrates. This vibration then sets the ossicles of the middle ear in motion. These ossicles then transmit the vibration to the hearing organ called the cochlea, which constitutes the inner ear.
The cochlea contains thousands of sensory hair cells. When sound reaches it, it sends an internal shock wave through the cochlea. Each hair is finely tuned to detect a precise pitch; when this hair matches the shock wave, it bends and triggers a nerve impulse sent to the brain.
Prolonged exposure to loud noises can cause inner ear hearing loss, called sensorineural hearing loss. This damage comes from the stress exerted on the hair cells of the cochlea. Strained for too long, they can be damaged, which reduces auditory acuity.
Loud sounds can also, more rarely, cause hearing loss by perforating the eardrum. If a sound is powerful enough and exerts enough pressure on the eardrum, it can give way and a perforation appears in this thin membrane. Once punctured, the membrane vibrates less well, because some of the pressure escapes to the middle ear.
This scenario remains possible, but it is very unlikely and usually only occurs if you are very close to an explosion or a gunshot without hearing protection.
Other examples of loud sounds that can lead to hearing loss to varying degrees include: garbage disposal, motorcycle, diesel truck, helicopter, jackhammer, jet plane takeoff, blender, intense outside noise, alarm clocks, propeller plane or jet passing by, thunderclap (chainsaw), fireworks, gas mower, garbage truck, air conditioner, shouting conversation, farm tractor, washing machine, heavy traffic (urban traffic), rock concerts, and printing presses.
Conversely, some sounds present no danger to your hearing: normal breathing, birdsong, the quiet atmosphere of a library, the refrigerator or its humming.
Conclusion
In summary, hearing health is a capital to be preserved throughout life. Listening to your headphones at full volume, going to concerts often without hearing protection, and many other habits can contribute to hearing loss.
Above 70 dB, sound levels can cause lasting damage in the inner ear, and the louder the sound, the faster the damage occurs. If your hearing has decreased following noise exposure, it may be useful to have a hearing check-up with a hearing care professional and start a process to regain good hearing.
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Sources:
Physics of Nondestructive Evaluation: Sound | Iowa State University
What noises cause hearing loss? | NCEH | CDC
Ruptured eardrum (perforated eardrum) - Symptoms and causes | Mayo Clinic
