Let’s begin by taking a closer look at the musical instruments in a string quartet. 


These three instruments may look similar, but the sounds they produce are very different. Listen to one song played on each of these instruments. Do they sound different? 

Before we learn why these three instruments are different from each other, let us go back to the basics. How is sound produced? Why are some sounds louder or deeper than others?

How is sound produced?

Take any stringed instrument – violin, veena, etc. and pluck at the strings. Observe the string as it makes a sound.

Can you see the string moving back and forth rhythmically? This is called a vibration, and this vibration produces sound. Now, while the string is making a sound, hold it firmly. You will see that it no longer produces a sound.

Similarly, in any situation, sound is produced by a vibrating object. In the experiment conducted, we could see the string vibrate. However, in many cases the vibrations may not be visible to us, although we can still feel them.

​​How does sound travel?

A little experiment: First, call out your friend’s name loudly. Carefully observe the loudness of your voice. Now, cup your hands around your mouth and call your friend’s name again. Does your voice sound louder?

Sound needs a medium to travel. We can hear sound because it travels through air. In this case, air is the medium. So why does your voice sound louder when you cup your hands around your mouth? It’s because, you trap a little more air around your mouth and the increased amount of air makes your voice sound louder. 

Similarly, if we were to remove all air from a certain area, there would be a vacuum in its place. In this case, we wouldn’t be able to hear at all, because sound cannot travel through vacuum.

Now, before we start understanding how the violin, viola, and cello are different in their sounds, let us learn a few key terms.

Frequency: We already know that the to and fro movement of an object is called vibration or oscillation. The number of oscillations per second is called frequency, and is measured by the unit Hertz (or Hz for short).

Pitch: Why does a drum produce a “deep” sound while a whistle produces a “shrill” one? The answer lies in the frequency. When objects vibrate with a higher frequency, their pitch is high. In other words, the sound produced is “shrill.” When they vibrate with a lower frequency, the sound is produced at a lower pitch. Look at the diagram to understand this more clearly.

String Tension: When a string is stretched tight across an object (like the body of the violin or cello), the force experienced when you tug the string is called tension. When the string is stretched very tightly, the frequency increases when you tug them, which in turn increases the pitch or shrillness.

Friction: The force that opposes the motion of an object is called friction. The reason for friction is two objects coming in contact with each other. In this lesson, it’s important to understand friction because it explains why we have to draw a bow over the strings to create different kinds of music.

1 – The Cello 

Let us start with the biggest instrument in the string quartet: the cello.  

If you compare the sound produced by a cello to the sound produced by a violin or viola, you will notice that it produces both deep and shrill sounds. To know why, it’s important to first know that the sound produced is affected by two major factors:

  • String length: When the string length is changed, it starts vibrating at a different frequency. Have you noticed that when you press your finger on a string, the sound becomes more shrill? That’s because the length of the string is shortened, which means it now vibrates at a higher frequency. In turn, the pitch is higher. In the case of the cello, the strings tend to be longer. This means it tends to produce deeper sounds, since the strings vibrate at a lower frequency.
  • String thickness: When the string is thicker, it will naturally vibrate at a lower speed. In turn, the frequency is low. As a result, the pitch is low.

However, a cello has four strings of different thickness. This means that the cellist can produce either a high-pitched sound or a low-pitched sound.

It is said that the cello can produce a wide range of sounds – from shrill to deep. Now that we understand the effect of string length and thickness on the frequency, we now know why a cellist can play such a diverse melody.

How do cellists produce the actual sound? With the bow. We now know that friction is caused by two bodies coming into contact and opposing each other’s motion. If it weren’t for friction, the cello would never make a sound. When the bow is drawn over the strings, the friction created is what causes the strings to vibrate at different frequencies and produce a difference range of sounds. To help create this friction, musicians use rosin – a hard and smooth substance made from plants. When rosin is applied to the horse hairs of the bow, it helps create friction between the bow and the strings.

2 – Violin 

Now, let’s take a look at the violin. 

When learning about the cello, we saw that its sound is primarily affected by string length and thickness. Let us see how these factors apply to the violin. 

  • String length: We already know that when the length of the string is shorter, it starts vibrating at a higher frequency, thus producing a high-pitched sound. In the stringed instruments family, the violin has the shortest strings. This is one of the reasons why the sound produced is higher in pitch.
  • String thickness: Compared to the cello, the violin’s strings are thinner. When the violinist either plucks at the strings or draws the bow over them, the strings vibrate at a higher frequency, thus producing a higher-pitched sound.

3 – Viola 

The last instrument in this lesson is the viola (pronounced “vee-oh-la”). It may look very similar to the violin, but there are many differences between the two instruments. Some of them are:

  1. The viola is larger than the violin
  2. The viola produces a lower-pitched sound
  3. The viola has a wider range of sounds (low-pitched to high-pitched) produced when compared to the violin

Now, let us look at the way string length and thickness play a role in the sound produced by the viola:

  • String length: The string length in the viola is shorter than that of the cello. Therefore, the strings vibrate at a higher frequency, creating a higher-pitched sound in comparison.
  • String thickness: While the viola’s strings are also of varying thickness, the range isn’t as high as when compared to the cello. While the cello is capable of producing a range of sounds in different pitches, the viola’s sound is consistently considered to be in the lower-pitched range. 

Note to Parents and Educators

The idea behind exploring the science behind music is to encourage children to draw parallels between music and the world around them. If you would like to explore the idea of helping your child or student develop critical thinking through the power of the arts, talk to us about our SaPa in Schools program. Click here to get in touch.

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