[Physics Class Notes] on Tone Pdf for Exam

When we hear the guitar sound, its vibration enters our ears. So, what is sound?

A sound is a type of vibration that enters our ears, besides, the frequency of a guitar sound should lie between 20 – 20 kHz to be audible or recognizable by our ears.

In acoustics, a tone is a sound that we can recognize by the regularity or continuity of its vibration.

A tone generally refers to a single frequency. However, the sound is a mixture of several frequencies, indeed sound is a mixture of tones.

On this page, we will understand the concept of tone and sound in detail.

What is Tone?

A tone is a musical or vocal or a melodious sound with reference to its pitch, quality, and strength/intensity. Thus a sound of single frequency is called tone; however, its intensity can vary.

Different Types of Voice Tones

Two different types of voice tones are as follows:

Firstly, a simple tone as we know is a single frequency sound whose intensity varies accordingly.

Secondly, a complex tone is a mixture of several simple tones, also known as overtones. Further, the tone of the lowest frequency is the fundamental overtone.

Additionally, the frequencies of the overtones can be whole multiples, i.e., 2nd, 3rd, 4th multiple.

Therefore, we call these fundamental frequencies, second, third, and fourth harmonics of the fundamental tone, itself known as the first harmonic.

Consequently, a combination of harmonic tones is pleasant to hear, and therefore, we call it a musical tone.

A tone is a single frequency sound, so now we will proceed further with the Physics of Sound.

The Physics of Sound

Assume the simple motion of a moving string. The instrument can be a violin, a guitar string, piano, sitar, or banjo string, which excites movement by plucking, striking/bowing it.

As a matter of fact, it makes no difference because the acoustic laws are the same for all instruments, no matter the type of principle they agree upon.

While looking at the below diagram, you might wonder how does the violin string move? And why is this sound considered musical?

Well! The answer to both questions is harmonics. Harmonics are different ways of movement of vibrations, happening simultaneously.

Indeed, harmonics are different ways of movement (inside the same body), occurring at the same time (instantly combining as a mathematical sum of the parts). The string moves similarly because, inside it, different types of movement occur at the same time.

Also, we hear a musical sound because all the vibrations are occurring simultaneously and give a beautiful sensation to our ears.

Therefore, the process through which various movements are happening at the same time inside one body is that of addition. The string of the violin vibrates at many of its resonant frequencies or harmonics simultaneously. By simply adding them, the resulting shape is that of a bowed string, as shown below:

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Point To Note:

The summing of all the parts or dotted vibration implies the simple (algebraic) addition of every point along the lines.

When all shapes are above the dotted, neutral line, they add up. However, when they are on the neutral line, their value is zero. If one or all of them are under the neutral line, they get subtracted.

Harmonic Motion

Harmonic motion is the occurrence of vibrations simultaneously. The term “harmonic” refers to the fundamental frequency of a waveform. Its types are:

First harmonic motion
Second harmonic motion
Third harmonic motion

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First Harmonic Motion

The first type of movement is the simple motion or the first harmonic motion.

All the sounds around you enter your ears as beautiful holographic bubbles, as you see in the image below:

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This simple up and down like a jump rope movement over the entire length of the string is the first harmonic motion.

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Second Harmonic Motion

The second type of movement of vibration splits the string into two identical though opposite parts, each oscillates in a fashion similar to the first harmonic.

When one of the halves of oscillation is up, the other is down, and vice-versa. This is what we call the second harmonic motion.

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In the second harmonic motion, we have two parts, i.e., node and antinode. So, let’s see what these are:

Nodes

The points that appear to be still standing (or do not undergo displacement) along with the medium are Nodes.

Antinodes

Particles that undergo maximum displacement between two points are antinodes. The nodes can be both positive and negative. The below figure illustrates nodes and antinodes:

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Third Harmonic Motion

In a third harmonic, we keep the node at both ends of a string so that the resulting wave pattern comprises four nodes and 3 antinodes.

It means that in a third harmonic motion, the waveform has a full sinusoidal wave cycle and one-half cycle. The diagram is as follows:

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Another term that we use in the Tone and Sound concept is a note. So, let’s understand this term:

What is a Note?

A mixture of several frequencies produces a sound that is pleasant to hear. This pleasant sound is called the note.