Class VIII Science
Notes for Sound
Sound is a form of energy and it comes from vibrations. These vibrations create sound waves which move through mediums such as air and water before reaching our ears. Understand how sound waves come from vibrations in the form of compression and rarefaction and how your ears give you the ability to hear them.
The difference between Musical sound and noise - Music is produced by periodic vibrations, having regular wave pattern e.g. sound of musical instruments. Noise is produced by irregular vibrations, having irregular wave pattern. e.g.. sound produced by moving vehicle.
Learn about the characteristics of sound.
   Loudness-It distinguishes between loud and feeble sound.
   Pitch-It distinguishes between shriller and flatter sound.
   Timbre or quality-It distinguishes one sound from other having same loudness and pitch.
Learn about free(natural ) vibrations - When we strike the keys of a piano, various strings set in vibrations at their natural frequencies in absence of any external force on it. Damped vibrations - When a body is made to vibrate in a medium, the amplitude of vibrating body continuously decreases with time and ultimately body stops vibrating. Such vibrations are called the damped vibrations.
When we want to tune a radio or TV set, we merely adjust the values of electronic components to produce vibrations of frequency equal to that of radio waves which we want to receive. Learn how this matching is done due to resonance. Resonance is the phenomenon when the frequency of an applied periodic force is equal to its the natural frequency, the body readily begins to vibrate with an increased amplitude. Understand the conditions of resonance and forced vibrations.
Sound needs a medium to propagate
The traveling of sound is called propagation of sound. Sound cannot propagate in the absence of a medium. The place where there is no air or air is removed, is called vacuum. Sound does not propagate (travels) through vacuum.
Sound travels through solid, liquid and gas.
We usually hear sound which comes to us through air.
Aquatic animals communicate as sound travels through water also.
We hear the sound through ear
Vibrations Produce sound
How is sound produced? From loudspeakers to guitars, all sound-producing devices share one common feature: vibration. The amount of vibration, as well as the speed of the vibration, produce the different sounds our ears can recognize.
In this blog post, we�ll look at the science behind sound and study how instruments like the guitar and piano create sound. We�ll also look at how modern hi-fi systems produce sound, as well as factors that can affect the clarity of sound.
The science behind sound
In simple terms, sound is vibration. The complex internal structure of our ears can respond to the waves produced by vibration, whether in the form of bass drum or an acoustic guitar.
When an instrument produces vibrations, it creates oscillating sound waves. Some of these waves are audible to humans, while others are very deep or high-pitched, and fall outside the human range of hearing.
A variety of metrics are used to measure sound�s intensity, volume and pitch. The pitch of sound is measures in hertz. One hertz (Hz) refers to the complete cycle of sound waves per second. Thus, 5,000Hz is equal to 5,000 cycles per second.
The human ear can generally perceive sound between 20Hz and 20,000Hz. Animals can often hear sound that humans can�t. For example, dogs can hear sounds at very high frequencies � often above 20,000Hz � but cannot hear low frequency sounds.
How instruments produce sound
All sound is created through vibration. In fact, some people can perceive sounds by focusing solely on the vibration an instrument creates. Ludwig van Beethoven, who famously went deaf late in his life, continued to compose by using the vibration of his piano to �listen� to his compositions.
Sound requires two components to be audible to the human ear: vibration, as well as amplification. Amplification can be provided by physical devices like the hollow body of a guitar, or by electrical hi-fi systems and speakers.
Let�s start with the guitar. Acoustic guitars produce sound through the vibration of their strings. This sound is amplified by the guitar�s hollow body, and the different strings each produce a different frequency � and thus different pitch � of sound.
The neck of a guitar contains anywhere from 12 to 24 frets. By pressing on each of these frets, the player changes the tension of the string, leading to a new frequency and a different pitch of note or chord.
On a piano, sound is created in almost exactly the same way. Instead of plucking the strings, piano players push keys which trigger hammers that push the strings inside the piano. The body of the piano amplifies this sound just like the body of a guitar.
While other instruments use different methods to create vibration and sound waves, the principles are the same: sound waves are created through vibration, and pitch is manipulated by changing the frequency of the vibration and sound waves.
How speakers produce sound
If you�ve ever taken the protective covers off a pair of hi-fi speakers, you�ll know that they vibrate when you play music. Speakers produce sound using vibration, just like a piano or guitar. However, the design of speakers lets them create a far wider range of sounds than a piano or guitar could produce.
Instead of using human energy to create vibration, like the plucking motion used to play a guitar or the tap of a piano key�s hammer, speakers convert electrical energy into vibration which, in turn, produces sound. Digital audio production software often includes a live view of sound waves as they are playing. The peaks in this view are the periods at which sound is loudest. This is when your speakers will be vibrating the most.
Most speakers include several different speaker drivers, each of which can produce sounds of a certain frequency. The most common speaker drivers include tweeters, mid-range, woofers, and subwoofers.
Sound clarity and acoustics
Have you ever heard an echo in a large room? Echoes occur when the sound waves produced by an instrument (including the human voice) or loudspeaker bounce off surfaces and travel back into your ears.
Echoes can occur in live venues such as stadiums, or in enclosed spaces like lounges and living rooms.
One of the biggest challenges audio engineers and producers face is reducing echoes in studios and live performance venues.
Since sound is created by vibration, the best way to reduce echoes is by installing a material that absorbs energy. This is why most studios have foam padding on their walls, or thick carpets designed to prevent sound reflecting and causing an echo.