Sound is a form of energy that travels in waves through a medium, such as air or water. We perceive sound as a sensation of hearing, which depends on various factors, such as the frequency, amplitude, and quality of the sound waves. In this article, we will focus on one of these factors, namely the amplitude, and how it affects the loudness of sound.
Contents
What is Amplitude?
Amplitude is a measure of the size or magnitude of a sound wave. It is related to the amount of energy that is carried by the wave. The greater the amplitude, the more energy the wave has, and vice versa. Amplitude can be measured by the height of the wave from its resting position, as shown in the figure below.
Figure 1: Amplitude of a sound wave
What is Loudness?
Loudness is a subjective perception of how loud or soft a sound seems to a listener. It is not a physical property of sound, but rather a psychological response that depends on various factors, such as the sensitivity of the ear, the distance from the source, and the background noise. However, one of the main factors that determines loudness is the intensity of sound.
What is Intensity?
Intensity is a measure of the amount of energy that passes through a unit area per unit time in a sound wave. It is proportional to the square of the amplitude of the wave, which means that if the amplitude doubles, the intensity increases by four times. The unit of intensity is watt per square meter (W/m2), but it is often expressed in decibels (dB), which is a logarithmic scale that compares the intensity of a sound to a reference level. The reference level for sound intensity is usually 10-12 W/m2, which is the threshold of human hearing. The table below shows some examples of sound intensity and corresponding decibel levels.
| Sound Source | Intensity (W/m2) | Decibel Level (dB) |
| Threshold of hearing | 10-12 | 0 |
| Whisper | 10-10 | 20 |
| Normal conversation | 10-6 | 60 |
| Lawn mower | 10-3 | 90 |
| Jet plane | 10-1 | 120 |
| Rocket launch | 102 | 170 |
Table 1: Sound intensity and decibel levels
How is Loudness Related to Amplitude?
According to Vedantu1, there is a relationship between the loudness of a sound and its amplitude. In general, loudness refers to how large the amplitude of the sound wave is. The decibel (dB) scale for measuring loudness is directly proportional to the square of the amplitude of the vibration. Thus, noise is defined as sounds above 80 dB.
This means that sounds with higher amplitudes have higher intensities and higher decibel levels, and therefore sound louder to our ears. Conversely, sounds with lower amplitudes have lower intensities and lower decibel levels, and therefore sound softer to our ears.
For example, a whisper has a low amplitude and a low intensity, and it sounds very soft to us. On the other hand, a jet plane has a high amplitude and a high intensity, and it sounds very loud to us.
However, loudness is not only determined by amplitude, but also by other factors, such as frequency, quality, distance, and background noise. For instance, two sounds with the same amplitude may have different frequencies, which affect their pitch and tone quality. A high-pitched sound may seem louder than a low-pitched sound with the same amplitude. Similarly, two sounds with the same amplitude may have different distances from the listener, which affect their attenuation or loss of energy as they travel through the medium. A closer sound may seem louder than a farther sound with the same amplitude. Moreover, two sounds with the same amplitude may have different background noises, which affect their contrast or difference from other sounds in the environment. A sound in a quiet room may seem louder than a sound in a noisy street with the same amplitude.
Therefore, loudness is not an absolute measure of sound, but rather a relative one that depends on various factors.
Conclusion
In this article, we have learned how the loudness of a sound is related to its amplitude, which is a measure of the size or magnitude of a sound wave. We have also learned that amplitude affects the intensity and the decibel level of sound, which are physical measures of sound energy. However, we have also learned that loudness is not only determined by amplitude, but also by other factors, such as frequency, quality, distance, and background noise, which are psychological factors that affect our perception of sound. Therefore, loudness is a subjective sensation that varies from person to person and from situation to situation.
