Hearing Mechanism – How do we hear sounds?
The human-ear consists of three major parts: Outer Ear, Middle Ear, and Inner Ear (Figure 1), where each part consists of various “components” that does their specific functions.
- Outer Ear – Consists of the pinna, ear canal and the tympanum (widely known as the eardrum)
- Middle Ear – Consists of the ossicles, made up of the three smallest bones in the human body: Malleus, Incus and Stapes
- Inner Ear – Consists of the cochlea
The main function of the ear is the gathering, transmitting, followed by the perceiving of sound from the surroundings. As mentioned, each part of the ear works differently, where they can be classified into three stages that relates to the parts of the ear respectively:
This proves that every-single-part in the ear plays an important role in our hearing system. Any impaired functions in the above stages will result to hearing issues.
Frequency range of human hearing
Typically, the human ear has the capability of hearing sounds from 20 Hz to 20 kHz, in which it is most sensitive at 500 Hz to 4 kHz. This range is also known as the Speech Range. The hearing efficiency of the human ear drops when the sound is at low and high frequencies. For example, the deeper the sound (lower frequency), the higher the volume of sound must be for us to be able to hear it.
Indeed, humans are incapable of hearing sounds from the infrasonic range. However, studies have shown that infrasonic can affect our body. Even though we cannot hear the infrasonic sound waves, they have the power to disturb human beings’ balance nerve, leading to symptoms like nausea, restlessness, headaches, and tinnitus. A common effect is seasick. Infrasonic sound waves can cause tiredness and disrupts sleep as well, thus poorer sleep quality.
The usual sources of infrasonic sound waves are machines or vehicles. These objects tend to produce very low-frequency sound that is very loud at the same time. Therefore, people who work in an environment that contains large machines or large ventilation system are more viable to infrasonic exposure. Since infrasonic waves move at very low speed with a long wavelength, they usually exist only in large halls and open office spaces longer than 20 metres. To avoid the infrasonic sounds from affecting the hearing system, it is best to keep a distance from the source as far as possible, otherwise one should wear special sound-absorbing ear defenders for protection purposes. https://www.hear-it.org/infrasonics-the-silent-enemy (Hear-it, 2010)
Effects of Noise on the Hearing Mechanism
When the ear is exposed to loud noise for a long period, it may lead to damage in hearing, where the level of seriousness can range from temporary hearing loss, to permanent hearing loss. At the early stage of hearing loss (temporary), the cilia are flattened, however the hearing ability will return after a short moment getting away from the noise coverage. Whereas for permanent hearing loss, the cilia, which are the hair cells in the ear, will be damaged fully. This leads to the destruction of hearing ability, that can never be restored naturally (DOSH, 2016).
Aside from hearing loss issues, long-term noise exposure can also lead to other health problems, such as increased heart and breathing rate, hypertension, low sleeping quality, lack of concentration, fatigue and feeling aggressive. So, do not ever think that noise will only affect your hearing!
But…are there other reasons for hearing loss? Of course.
In the section below, we will discuss more on the various aspects of hearing loss.
Indeed, noise induced hearing loss is quite common especially in the occupational field. But there are also other causes. One major one would be age-related hearing loss, also known as Presbyacusis, which cannot be avoided much as you age. Hearing loss can sometimes be caused by ototoxic drugs or chemicals, trauma, injuries, and even tumour. Therefore, it is important to always keep track of your hearing ability!
To know whether you may be suffering from hearing loss, these are the common signs:
- Difficulty in hearing someone speak
- Unable to hear high-pitched or very soft sounds
- Hearing noise or ringing in the ears
- Keep getting complaints that your radio/television is too loud
- Having trouble in understanding conversation at a distance or in a crowd
- Trouble hearing something that other people can easily hear
Once again, it is extremely important to take note of your hearing abilities because there is no cure for hearing damage! Even though the use of hearing aids can improve the hearing ability, it does not restore noise-damaged hearing. So, the best method is to prevent hearing damage at the earliest stage!
DOSH, D. O. O. S. A. H. M., 2016. Introduction of Noise and Legal Requirements, s.l.: s.n.
Hear-it, 2010. Infrasonics: the Silent Enemy. [Online]
Available at: https://www.hear-it.org/infrasonics-the-silent-enemy
[Accessed 2 August 2020].
Written by Khei Yinn Seow
Posted on August 19, 2020