Sometimes, we have certainties on which we would be happy to bet anything. Who doubts, for example, that humans perceive sounds only thanks to their ears? Probably nobody.
In reality, we do not hear only through our outer ear, but also via our skull bones that can communicate to the inner ear, thanks to the phenomenon of bone conduction.
This is the first article in a series on this type of sound conduction and we will explore together how it works and its interesting applications.
Let’s start with the answers to three simple questions:
1. What is it and how does bone conduction works?
Before explaining how sound propagation happens through bone conduction, we need to understand the sound path through the auditory system.
The human ear is divided into three parts: the outer, middle and inner ear.
The sound wave, in the form of air vibrations, enters into the auricle (external ear) and reaches the eardrum. The tympanic membrane changes the nature of the sound wave vibrations, propagating them as mechanical vibrations through the ossicles (middle ear). Finally, the sound wave is transmitted to the cochlea (inner ear), and it is transformed into electrical impulses which will be processed by the brain.
Now, to get a real feeling of what bone conduction is, I invite you to make a curious experiment. If we take a piece of wood, we hold it between our teeth and we let its end touch a vibrating sound source, we will make a very special experience. We will hear, clear and crisp, the sound of the sound source, but we will also have an unusual feeling: we will feel the sound not coming from our ears but, instead, directly from inside our head. This is not an illusion, it is what is actually happening!
This is because our bones are excellent conductors of vibrations and also the upper and lower jaw can contribute to our perception of sounds. In this case, instead of travelling through the air, as typically happens, the sound signal is conveyed from the cranial bones that transmit it to the innermost part of the ear, and then continues the normal route to the brain. With bone conduction, the outer ear and ear drum are simply bypassed.
Another concrete example of this phenomenon? Try to record your voice and listen to it again: you will realize that it sounds very different from the way you’re used to hear while you are talking. The difference is due to the fact that we hear our voice mainly through its internal propagation via the skull, rather than through the our ears. We can tell the difference because the cranial bones transmit better low frequencies than air does, so our voice sounds lower and more intense.
2.What is an interesting application of bone conduction?
A particular application of sound transmission via bone conduction is starting to spread among the general public: bone conduction headphones. This type of headphones are placed between the maxilla and the mandible, right in front of the ears, leaving the ear completely free.
3. How do bone conduction headphones work?
Common earphones contain a thin membrane that produces sound by generating air vibrations. Bone conduction headphones, instead, use an electromechanical transducer that plays the same role of our eardrum. It receives the sound signals, it transforms it into vibrations suitable to be propagated through the bone and, by being positioned adjacent to the middle and inner ear, it passes the vibrations on to the bones, and then the sound continues its regular route through the auditory system.
What are the advantages of bone conduction headphones?
After finding out what bone conduction is and understanding how the bones of our skull effectively propagate the sound, we can now explore the three main benefits of headphones that use this type of sound transmission:
- Thanks to the fact that they do not obstruct in any way the ear, bone conduction headphones, are particularly suitable when the user wants to keep the contact with its surrounding environment. They are ideal for drivers, cyclists who want to juggle crossings and, at the same time, want to listen to the radio or simply to talk with their teammates. They are also ideal for runners who want to listen to music without missing the sounds of the parks they are running through. In fact, it’s not a suriprise that the current manufacturers of this type of headphones are mainly targeting athletes.
- Even more remarkable is the extraordinary usefulness that bone conduction headphones have for blind and visually impaired people. For them, hearing is the first sense to rely on for the perception of the surrounding environment. Each lost piece of auditory information can be a problem or even a danger for these users, for example, when crossing the road. Bone conduction headphones are the perfect solution under such circumstances, and help prevent the information loss from the surrounding environment.
- The usefulness of this type of headphones increases exponentially, particularly for blind and visually impaired users, when they are combined with a smartphone, giving access to important sources of real-time information like: navigation services, the status of public transport lines, the weather, news and music, just to name a few.
Visually impaired people use screen readers and voice guides, to make extensive use of these devices, allowing them to be much more autonomous and greatly increase their quality of life. With these type of headphones, paired with a smartphone, it will no longer be a problem to make calls, listen to music, listen to the voice of the screen reader, while still being vigilant on everything that surrounds you.
In a nutshell, bone conduction stereo headphones, create a new kind of experience we might call “augmented sound reality“: no more more earbuds in your ears, instead, the freedom to hear both the sounds from the device and the environment without any interference.
If you too have used bone conduction headphones at least once, tell us about your experience! Please do post a comment below!
In the next article we will reveal some more interesting facts about this fascinating technology, do not miss it!
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Questo articolo è disponibile anche in: Italian