What is sound, shouldn't we think about this indispensable piece of our lives at least for once, be curious about it and research it?
What would our world be like in its absence, how would we feel? The sound is a really simple thing for us who can hear and as a natural outcome can talk. But is it really like that? What is the level of our awareness of hearing and talking? OK, I admit, before my audiology masters education, I also wasn't fully aware of this important miracle...
<center>![469508.jpg](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513623067/bmuese1yeczg1jrnw12e.jpg)</center><center>[image source](http://getwallpapers.com/wallpaper/full/4/2/1/469508.jpg)</center>

### What is sound?
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If you are a child, your mother is the sound, if you are a singer, its the biggest talent that has been given to you. If you are a pianist, the magic on your fingertips is the sound. If you are a teacher, it is a pain in the neck that gets hoarse together with a hurting throat. For physicians, it is the molecular distribution of an energy source in the air or if you are a clinician, the sound is the stimulant of the sense of hearing.
It is of course very possible to increase the examples but no matter how much examples there is, there is a fact that is unchangeable; the sound is our lives maybe simplest but yet the most necessary color...

### OK, a little **physics** then
<center>![soundwaves_1.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513627698/vcuk3vuvxanblju5wabg.gif)</center><center>[image source](http://ffden-2.phys.uaf.edu/211_fall2013.web.dir/Molly_Tedesche/soundwaves_1.png)</center>

**Sound** is a mechanical vibration wave that spreads in a medium made of matter. It is an energy form, just like electric and light. The **compression and rarefaction** of air molecules make sound waves.

Air is an elastic matter. It has over 60 billion particles per cm3 and by this specialty, it is the best sound conductor. Air is not the only thing that conducts sound, sound can be conducted through liquids and solids too. A little side note here about the way we hear sounds; the two ways of us hearing sounds, through the air and through the bones.
Hearing through the bones: To give a simple example, it is the sound we hear when eating chips. Here, the skull bones are serving as a conductor and the sound mostly travels through our skull bones rather than the air.
<center>https://media.giphy.com/media/oF40bAXBuiv0k/giphy.gif</center><center>[source](https://giphy.com/gifs/wave-sound-educational-oF40bAXBuiv0k)</center>

### Energy is spreading in the form of waves...


A **Sound Wave** has a fixed amplitude and a single frequency and we call this a **sinus wave**. A sinus wave is formed of 2 phases, positive and negative. It creates a sinus wave that forms depending on the position changes of the particles.

**Frequency of Sound**

The cycle of compression and rarefaction that particles create in a second is called, the frequency of sound. The unit of frequency is Hertz(Hz). It was defined by the German physician [Hertz](https://www.britannica.com/biography/Heinrich-Hertz), in the 19th century.
As the frequency rises, the pitch of sound gets higher. **Chest** notes form as the frequency gets higher.
We can only hear the sounds that are in between 16 to 20.000 Hz. Subsonic(<16Hz) or Ultrasonic(>20.000Hz)
The frequencies of our speech sounds are usually in between 500 to 2000Hz.
This is different in other creatures. The upper limit for rabbits is 30.000Hz, for bats; 60.000Hz, for dolphins; 140.000Hz and for butterflies it is 160.000Hz.
<center>![preliminary-physics-world-communicates-2-8-638.jpg](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513623321/bmrja0i2bcvsc3gplquf.jpg)
</center><center>[image source](https://image.slidesharecdn.com/worldcommunicates2-141030161601-conversion-gate02/95/preliminary-physics-world-communicates-2-8-638.jpg?cb=1414685802)</center>

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### Speed of sound

I'm sure we have read this everywhere. Maybe the biggest specialty of sound, thanks to Concorde planes...

<center>https://media.giphy.com/media/DHAOO6IAJXTI4/giphy.gif</center><center>[source](https://giphy.com/gifs/speed-sound-propagation-DHAOO6IAJXTI4)</center>

The speed of sound in air is 344m/s, but the air temperature is also a factor here, and this value is valid for 21 Celsius degrees. In water, it is 1480m/s, and in **our own body, the speed of sound** is; **1588m/s**, almost **5** times its speed in air. 

>‘’**If a person is closed in a silence room which is built with special isolations, a rumor says it that there has never been anyone surviving for more than half an hour. In this infinite silence; the sound of our body, our heart, the blood in our veins, the sound of friction of our skin, the exhalation of the air in our lungs, creates stress on the brain after some time and people say that it is an unbearable sound.’’** The reference to this information is my audiology [professor Mr. Soner Özkan](http://www.kbb.hacettepe.edu.tr/personel/ozkan.php) (may he rest in peace)


The speed of sound is inversely proportional to the distance from the source. Also, the sound waves are reflected, absorbed or conducted according to the properties of the obstacles it opposes.

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### Wavelength and intensity
The sound spreads as longitudinal waves. The distance sound covers in space is called wavelength.
It is related to **Wavelength(W)**, **frequency(Hz, cycle/sec)** and **speed(m/sec)**.
<center>W=v/f</center>
At high frequencies, the wavelength will be short, and at low frequencies, it will be long.
<center>![radio_spectrum_large.jpg](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513623751/vxokzgkysuhy1nibvimo.jpg)</center><center>[image source](https://www.nasa.gov/sites/default/files/radio_spectrum_large.jpg)</center>

So, the most important specialty of sound for us: **intensity**
It is about the volume of sound that our ears hear. Or let me put it this way, The average amount of energy that passes through a unit area in unit time is the intensity of sound. **(Watt/cm2)** The lowest intensity of sound that human ear can hear is **10<sup>16</sup> Watt/cm2**. And this value is accepted as **"0" in terms of dB.**

### Decibel(dB)
This term which is named Bell,  in tribute to Alexander Graham Bell, is defined as the smallest sound that human ear can hear. In audiology clinics, they use decibel(dB) which is 1/10th of a Bell. 
Our whispering sound has an intensity of 30dB, speaking; 40 to 60dB and the sound of a plane lifting off has 140dB.

<center>![typicalsoundlevelscr.jpg](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513625037/z3injvjkjz8kxpm9gpc4.jpg)
</center><center>[image source](https://www.alexandriava.gov/uploadedImages/tes/info/typicalsoundlevelscr.jpg)</center>
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Note: If you are exposed to high volume sound, to protect your ears, opening your mouth to max while you are closing your ears with your hands will distribute the pressure you are exposed to.This already is the general behavioral reflex of humans against a very high volume sound. We close our ears, open our mouth and we also do one more thing; we kneel down on our knees. And the reason for this is to be exposed to the sound coming in form of waves from a smaller area...

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Thank you for reading, and please just close your eyes and listen to yourselves and your surroundings, maybe it is telling us the secret of life, can it be?
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references:
* [https://www.britannica.com/](https://www.britannica.com/science/sound-intensity)
* [https://www.sciencedaily.com/](https://www.sciencedaily.com/terms/speed_of_sound.htm)
* [https://physics.info/sound/](https://physics.info/sound/)