Chloe at the concert
Relationship between sound level and distance from the source
Autor:
Título 4
Learning objectives :
This activity allows students to understand the relationship between sound level and distance from the source. It raises awareness of the hearing risks linked to exposure to high sound levels.
Concepts covered
Sound propagation; Logarithmic decibel scale; Relationship between sound power and distance; Hearing health; Risks linked to high intensity sounds
What students will do :
The student uses two smartphones to measure the impact of distance on sound level: one emits white noise via FizziQ's sound library while the other measures the noise level at different distances. By comparing the measurements and analyzing the differences observed, the student checks whether the initial statement is correct and reflects on the implications in terms of hearing health.
What is required :
Two smartphones with the FizziQ application; A quiet space for measurements; A tape measure to precisely measure distances; FizziQ experience notebook
Scientific background :
The propagation of sound in air follows the inverse square law: sound intensity decreases proportionally to the square of the distance from the source. This relationship is explained by the spherical dispersion of sound energy from the point emitting source. For an omnidirectional source, the power P is distributed over the surface of a sphere of radius r, therefore the intensity I = P/(4πr²). However, we perceive and measure sound according to the logarithmic decibel scale: L = 10log(I/I₀). Therefore, when the distance triples, the intensity is divided by 9 (3²), which corresponds to a reduction of approximately 9.5 dB. This difference is significant since an increase of 10 dB is perceived as a doubling of sound volume. The hearing risk level starts from 85 dB for prolonged exposure, and every 3 dB increase doubles the sound power. In a concert, levels can reach 100-110 dB near the speakers, well beyond the pain threshold (120 dB). Using the smartphone microphone with FizziQ provides reliable relative loudness measurements, although absolute values may vary slightly between models.