Making Sounds

Sounds are produced by different musical instruments in different ways. Listed below are the types of musical instruments and the sounds they make:

Musical instrument How they produce sounds Example
String instruments Sound is produced in a string instrument when they are plucked or bent. Guitars, electric guitars, violins, etc.
Wind instruments Wind instruments have an air column in them which is made to vibrate by blowing out air at the end of the air column. Flutes, bagpipes, etc.
Percussion instruments The instruments that are made to vibrate by striking them are called as percussion instruments. Drums, xylophones, gongs, bells, etc.

You may notice that all these instruments have one thing in common: they all make sounds using vibrations.

The speed of sound

The speed of sound is just 330 m/s in air at 00C.

The speed of sound is affected by two factors:

  1. The material it is travelling in
  2. The temperature it is travelling at

That’s why we have stated the material and the temperature while writing its speed.

Now let’s look at each of these two factors in detail:

Factors affecting the speed of sound
Material Temperature
Sounds travels fastest in solids The greater the temperature of a material, the faster the sounds will travel through it.
Sounds travels the slowest in gases
The speed of sound in a liquid is between its speed in solids and in gases.

 

Using Oscilloscopes

An oscilloscope is a device that can be used to see traces of sounds. The traces help demonstrate the loudness, the frequency and the pitch of sounds.

Uniform traces of sound can also be produced using a signal generator. A signal generator produces pure note which have a fixed amplitude, wavelength and frequency.

Pure notes help us calculate the frequency of the sound by using the equation below:

Frequency and pitch, amplitude and loudness

Frequency and pitch can be related to each other in the following way:

  • Higher the frequency, higher the pitch.
  • Higher the pitch, higher the frequency.

This shows that frequency is directly proportional to pitch

Similarly, amplitude and loudness can be compared as well in the following way:

  • Higher the amplitude, louder the sound.
  • Louder the sound, higher the amplitude.

Range of hearing

Generally the human hearing range stretches from 20 Hz to 20,000 Hz.

However, as people grow older, their upper limit of hearing decreases by 2000 Hz every decade.

A person’s upper limit of hearing is the highest frequency of sound that he/she can hear.

Ultrasounds and infrasounds

Sounds which have frequencies higher than 20,000 Hz are defined as ultrasounds.

Sounds which have frequencies lower than 20 Hz are defined as infrasounds.

How sounds travel

By now, you may know that sounds travel through vibrations. But writing this in your examination will merely fetch you a mark.

Here is a better picture of how sounds travel:

FUN FACT

Sounds cannot travel in vacuum. This is because there are no molecules in vacuum to vibrate and travel by compressions and rarefactions.

Compressions and rarefactions

If you’ve read the ‘fun fact’ given above, you may notice there are two important words mentioned: compressions and rarefactions.

Compressions are the areas on a sound wave where the air molecules are close together. The areas of compression on a sound wave are always represented by the crests.

Rarefactions are the areas on a sound wave where the air molecules are less closely packed together (or rarefied). The areas of rarefaction on a sound wave are always represented by the troughs.

 

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