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Tone and Sound

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:

  • Simple tone

  • Complex tone

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:

  1. First harmonic motion

  2. Second harmonic motion

  3. 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. 


Point To Note:

An octave comprises eight different notes, its frequency ranges from 256 Hz to 512 Hz. This is how an octave looks like:

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FAQs (Frequently Asked Questions)

Q1: How Can We Determine the Harmonic Frequencies of Sound?

Ans: A number of antinodes are equal to the integer multiples of specific harmonics, i.e., for the first harmonic, we have 1 antinode, further, for the 2nd harmonic we have 2 antinodes, etc.


We can calculate the harmonic frequencies by the following formula:


Speed = frequency x wavelength


V = n x  λ


For the nth harmonic, we have:

 

         nth harmonic = n x fundamental frequency


So, if we know the speed and wavelength of a waveform, we can calculate harmonic frequency. 


The types of harmonic in waves are even and odd harmonics. For example, a cylinder with both sides open vibrates at both ends, i.e.,  at even and odd harmonics. However, a cylinder with one closed side vibrates at odd harmonics only.

Q2: Imagine That Girl is Sitting in the Middle of a Park of Dimension 12 M X 12 Ft. on the Left Side of the Park, There Is an Apartment Adjoining the Park and on the Right, There is a Road Adjoining the Park. a Popped Cracker Produces a Sound Is it Possible for the Girl to Hear the Echo of This Sound? Explain Your Answer.

Ans: The answer is No.

For the girl to hear the echo of this sound, the minimum distance between the observer at the source of sound and the obstacle is 11.3 m. However, the distance between the girl and the obstacle (building) is only 6m approx, which is the reason she cannot hear the echo of the popped cracker.

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