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# Loudness

This lesson aligns with NGSS PS4.A

Introduction
Suppose, when a string of the guitar is plucked, it starts vibrating with a low amplitude. If we apply more energy and pluck the string more forcefully, the amplitude of the vibrations increases, resulting in a louder sound. It is observed that as the amplitude of vibration increases, the intensity of the sound. The concept of loudness refers to the perception of how soft or loud a sound is. In this article, we will learn about the term loudness, how loudness is related to amplitude, the relation between energy and vibration, and how we measure loudness.

Loudness
Loudness refers to the sensation of how strong a sound wave is at a place. For instance, if a bass drum is gently tapped, it produces a soft rumbling sound. However, if the drum is struck with greater force, a loud boom is heard. The loudness of the sound created can be altered by varying the force applied when striking the drum.

Relation between Energy and Vibration
When you strike a drum with greater force, the boom is louder. This means that a larger force transfers more energy to the drum, causing it to move with larger vibrations and transfer more energy to the surrounding air. As a result of the increase in energy, air particles vibrate farther from their resting positions.

Loudness is related to Amplitude
When you strike a drum harder, actually you are increasing the amplitude of the sound wave produced. The amplitude of the wave refers to the maximum distance that particles in a wave vibrate from their resting positions. Consequently, a larger amplitude results in a louder sound, while a smaller amplitude leads to a softer sound. In the mentioned figure, we can observe one method of increasing the loudness of a sound.

Measuring Loudness
Loudness is quantified using a unit called decibel (dB). The decibel scale is logarithmic which means that a small change in decibel levels corresponds to a significant change in sound intensity. For example, a sound that is 10 dB louder than another sound is 10 times more intense.

The weakest sounds that an average human ear can hear are at a level of 0 dB. On the other hand, the threshold of pain is often associated with sound levels of 120 dB and above, as they can cause discomfort and pain in the ears. Prolonged exposure to sounds exceeding 85 dB can lead to gradual hearing loss by permanently damaging the hair cells in the inner ear.

Examples of Loudness
• Whispering: imagine two friends sitting together, sharing secrets in whispering. This gentle sound registers around 20 dB and it is perceived as intimate and soft.
• Normal conversation: when engaging in a regular conversation, the sound level hovers around 60 dB which is comfortable and easy to hear.

The following table illustrates the decibel levels of various common sounds.

Oscilloscope
Because the sound waves are invisible, their amplitude and frequency cannot be directly measured. However, technology offers a way to visualize sound waves.

An oscilloscope is a device that is used for the graphical representation of sound waves. The process involves a microphone that converts the sound wave into an electric current, which is then transformed into graphical representations, as shown in the mentioned figure. Interestingly, the graph appears as transverse waves rather than longitudinal waves. The crests of these waves represent compressions, while the lowest point (troughs) represent rarefactions.  By looking at the displays on the oscilloscope, one can readily distinguish the difference in both the amplitude and frequency of sound waves.

Summary
• Loudness refers to how loud or soft a sound is perceived by our ears.
• The loudness depends on the amplitude of the vibration, a larger amplitude results in a louder sound, and vice versa.
• The most common unit used to express loudness is the decibel dB.
• The weakest sounds that an average human ear can hear are at a level of 0 dB.
• A device called an oscilloscope is used for the graphical representation of sound waves.

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