Sound is a form of energy, just like electricity, heat or light. When you strike a bell, it makes a loud ringing noise. Now instead of just listening to the bell, put your finger on the bell after you have struck it. Can you feel it shaking? This movement or shaking, i.e. the to and fro motion of the body is termed as Vibration. The sound moves through a medium by alternately contracting and expanding parts of the medium it is traveling through. This compression and expansion create a minute pressure difference that we perceive as sound. Let’s discuss the characteristics of sound waves like amplitude, frequency, wavelength, and timbre.
Traveling of Sound Wave (Longitudinal Wave):
In real life, we hear all sorts of noises, screaming, shouting, laughing and this is not just restricted to humans. Animals also make noises and these are distinctly different from the human voice. Does a drum make the same sound as a flute? So what’s the difference? To understand this, we will explore some of the basic properties of the sound waves.
When sound waves are represented in a waveform, we instantly notice some basic characteristics. The waveform is a pictorial representation of the pressure variation in the air which travels as sound. These waves are alternately regions of high pressure and low pressure. Thanks to the waveform, sound waves now seem very similar to light and other electromagnetic radiation.
A depiction of Sound Waves in Waveform and representation of Amplitude/ Loudness and Wavelength
This in light refers to the amount of energy in an electromagnetic wave and its meaning is the same here. Amplitude refers to the distance of the maximum vertical displacement of the wave from its mean position. Larger the amplitude, the higher the energy. In sound, amplitude refers to the magnitude of compression and expansion experienced by the medium the sound wave is traveling through. This amplitude is perceived by our ears as loudness. High amplitude is equivalent to loud sounds.
Two graphs showing the difference between sound waves with high and low amplitude
The waveform representation converts the pressure variations of sound waves into a pictorial graph which is easier to understand. A sound wave is made of areas of high pressure alternated by an area of low pressure. The high-pressure areas are represented as the peaks of the graph. The low-pressure areas are depicted in the Valleys. The physical distance between two consecutive peaks or valleys in a sound wave is referred to as the Wavelength of the sound wave. It is labeled in the image above.
Frequency/ Pitch of the Sound Waves
Frequency in a sound wave refers to the rate of the vibration of the sound traveling through the air. This parameter decides whether a sound is perceived as high pitched or low pitched. In sound, the frequency is also known as Pitch. The frequency of the vibrating source of sound is calculated in cycles per second.
The SI Unit for Frequency being hertz and its definition being ‘1/T’ where T refers to the time period of the wave. The time period is the time required for the wave to complete one cycle. Wavelength and frequency of a sound wave are related mathematically as:
The velocity of Sound = Frequency * Wavelength
The below graphs can be used for understanding more about sound. The first graph represents a sound wave from a drum while the second graph represents the sound wave from a whistle. You probably already know the difference in the sounds but have a look at the difference in their frequencies.
Two graphs showing the difference between sound waves with high and low frequencies and their corresponding pitches
Imagine a bell and a piano in an orchestra. The same musical notes can be obtained by both the instruments but their sounds are very different. The piano produces a distinct note whereas the bell struck to the same pitch and amplitude produces a sound that continues to ring after it has been struck. This difference in the sound is referred to as the Timbre. Timbre is actually defined as; if two different sounds have the same frequency and amplitude, then by definition they have different timbres.
In this article, you learn about the different characteristics of sound waves and how two sound waves of even the same amplitude and frequency can produce completely different sound. The world around you is filled with interesting facts like these. Learn all about them at BYJU’S.