I still remember how much I love to hear the theme music of Merlin TV series. It’s so emotional and make me calm within seconds. But it’s not the only emotional music I like to listen. There isn’t a single day that I haven’t listen to mind-blowing sounds – Musics – in last years of my life. As humans we are attracted by various sounds from songs to Howling (Sound of Wolf) and so on.
Actually sound is a wave, I explained it earlier on a post where I wrote about mechanical waves and electromagnetic waves. Ya! I know it wasn’t deep enough for you to realize the nature of sound waves. These waves belong to the mechanical longitudinal wave type and have so many properties and abilities.
There must be a some kind of vibration to form a sound.
Reflection of Sound Waves
It is inevitable for you to quickly realize how light waves reflect, because it is a thing that you can see from your eyes. What you see through eyes can be deposited in your mind better than what you hear with your ears. That’s why many times, photographs are used to teach small children effectively.
Similar to light waves, the sound waves too show properties of reflection.
Reflection is the change of direction of a wave. Suppose you have a mirror in your hand and you keep it under the sunlight and point it towards another direction. You’d see the light rays struck in the mirror and then jump to the direction you pointed the mirror.
Here’s a quick strategy to prove the reflection property of sound.
Take 2 water pipes with same length and diameter. Get 2 card boards and keep them together to form the English letter ‘T’, but make sure to keep some distance between the card boards. Now keep the 2 water pipes to form an angle as it is in the following diagram.
Play or make a sound from one water pipe while listening to it from other pipe. You’ll hear the sound on other side clearly.
Propagation of Sound
Sound wave propagation means the traveling of sound from one place to another. As you know a medium is required for all the mechanical waves, so sound waves too. Vacuum is not a place where sound can propagate. Not sure …?
Let me tell you a way to find it exactly. Here are the things you need.
– Electric Bell (Battery or other)
– Vacuum Pump
Set the bell to ring. Now remove the air inside the electric bell using the vacuum pump. Make sure you fit the vacuum pump tight so that air cannot go inside again.
First you’ll hear the bell sound, once you start to remove the air, the bell sound also starts to become slow and unclear. After removing all the air you won’t hear the bell sound anymore. So we can conclude sound waves cannot play in a vacuum.
I love inspirational facts, mind-blowing science theories and crazy numbers. Here are 3 number facts about sound waves.
- Sound velocity in air is 330ms-1
- And in water it goes up to 1,461ms-1
- In steel it further goes higher to 5,000ms-1.
Isn’t it a crazy number for steel?
Actually why numbers become higher for solid and liquid states? Air particles are not tightly packed together, but solid particles are tightly packed together. Therefore vibration will become faster because particles are near each other.
What is Echo of Sound?
You learned that the sound can reflect in the previous section of this post. Echo is something that happens due to reflection of sound. Echo means the reflected sound that you can hear after a time lag from the original sound.
This doesn’t mean you can hear each and every reflected sound or echo. Because the sounds you hear remains in the ears for 1/10 of a second. If the reflected sound comes quickly before 1/10 of a second, you will not notice the echo.
If the echo comes after above time frame, you can hear it as an echo.
Now let me do a quick calculation to reveal you the minimum distance between the source of sound and the reflection surface to hear the echo properly.
Velocity of sound in air → 330ms-1
Distance in 1 second → 330m
Distance in 1/10 of a second → 330m x 1/10
Minimum distance between source an surface → 33m / 2 = 16.5m
So lets round off the minimum distance to 17m. This is an accurate number for hearing a clear echo of a sound. There are different frequencies for sound waves, but the human ears got a limit between 20 Hz to 20,000 Hz. Therefore you can’t hear 10 Hz sounds nor the 20,100 Hz.
Do you know dogs can hear higher frequencies than 20K Hz. Such sound waves are known as UltraSound Waves.
You cannot hear the echo if the reflection of sound comes before finishing the initial sound in your ears. Instead of that you’d feel the initial sound is extended. Even though you can’t hear the echo, No … let’s say you can’t identify that echo.
Okay, let me call that incident or phenomenon as the Reverberation.
Sound waves reflect steadily on a smooth surface, but it doesn’t do so on a rough surface. That’s a reason for minimization of echo and reverberation.
So, What Are the Uses of Echo?
It’s time to talk about the benefits of echo. Usually echos are used to calculate the depth of the sea bed from the surface of water. In addition to that, there are few other uses of echo.
- Identify parts of sunken ships, submarines, planes and other sunken stuffs.
- Find fish shoals in deep water.
- Avoid interferences for under water vehicles such as submarines.
- Detect places which are rich with oil.
As all other stuffs in science, there is an instrument to use echo as Echo Sounder. It’s the apparatus which helps to find above stuffs easily.
These instruments can be seen in ships. Echo sounder can send an UltraSonic Sound wave from the surface of water to sea bed. Then this sound will reflect back to the surface of water after some time. We already know the speed of sound in sea water and the time taken to reach water surface can be measured.
Finally you can find the depth of sea bed or any other distance with a simple calculation.
Bats are using echolocation to skip the obstacles in their way when flying. Bats who use this ability can’t see properly. Therefore they send ultrasound waves and listen to the echo to detect trees when flying.
Characteristics of Sound
You hear various sounds as soon as you wake up till you sleep. Girls do have a soft voice while boys do have a rough voice. Then there are music notes which are high. These things happen because of the characteristics of sound.
Pitch of a Sound
There are few parts of a wave which I explained you in a previous post. One such part is known as Frequency. The pitch of a sound relies on the frequency of that sound wave. If the frequency is high, the pitch is high and the sound is sharp.
If the sound you hear is rough, it means its frequency is low and pitch too.
Loudness of a Sound
Do you have a drum or desk near you? Beat it slowly and listen to the sound. Beat it again hard and notice the sound again.
Simply the first sound wasn’t loud enough, but the second sound had a high loudness. Loudness of a sound depends on the energy coming as sound waves to your ears.
Do you have a Violin? It has strings which are stretched well. If you want to make a sound with guitar, you have to pluck the string with some amount of energy. If the pluck is harder the outputted sound is loud.
Notice the movement of string when vibrating hard. The height between the crest and trough is higher if you see it as a wave. You know that height is known as Amplitude of the wave. Remember higher amplitude will result in a loud sound.
Sound waves occurred from the source continuously loses its energy when vibrating for a long distance. So the amplitude of the sound also decreases. Therefore the loudness of the sound also decreases.
If you can increase the amplitude of a sound, it’ll have a good loudness.
Quality of a Sound
If two notes have same loudness and pitch, you can feel the difference of those 2 notes by quality of sound. Suppose you have a Violin and Keyboard and you play the same note in both instruments.
You can feel the sound is different in both instruments even the same note was played. That’s the quality of sound and the waves of the 2 instruments also different as the sound. Sound wave patterns can be tracked with an instrument called CRO – Cathode Ray Oscilloscope.
Once this instrument connected to the playing instrument, the wave pattern will be displayed in the screen.
Musicians use this characteristic of sound to tune their musical instruments.