The blog post explores the physics behind the distinctive "whoosh" sound created by passing objects like airplanes. It explains how this sound isn't simply the object's engine noise, but rather the Doppler-shifted frequencies of ambient noise—like wind, traffic, or conversations—being compressed as the object approaches and stretched as it recedes. This effect, similar to how a siren's pitch changes as it passes by, is most noticeable with fast-moving objects in relatively quiet environments. The post further delves into how our brains perceive these shifting frequencies, potentially misinterpreting them as the sound of the object itself and sometimes even creating phantom whooshing sensations when no physical source exists.
This blog post, titled "Passing Planes and Other Whoosh Sounds," penned by Windy Tan, delves into the fascinating auditory phenomenon of how the perceived pitch of a passing sound source, such as an airplane or a car horn, changes as it moves relative to the listener. This alteration in pitch, known as the Doppler effect, is meticulously examined and explained within the context of everyday experiences. The author meticulously deconstructs the underlying physics, elucidating how the compression and expansion of sound waves, caused by the motion of the source, result in the familiar shift in pitch. When the source approaches, the sound waves are compressed, leading to a higher perceived frequency and thus a higher pitch. Conversely, as the source recedes, the sound waves are stretched, resulting in a lower perceived frequency and a lower pitch.
Furthermore, the author elaborates on the specific scenario of a passing airplane, highlighting the unique "whooshing" sound often associated with it. This whooshing sound, as explained in the post, is not solely attributable to the Doppler effect but is also significantly influenced by the complex interaction of air flowing over the aircraft's surfaces. This aerodynamic phenomenon generates turbulent airflow, creating additional noise that contributes to the overall auditory experience. The post emphasizes that this combination of Doppler shift and aerodynamic noise creates the distinct auditory signature of a passing aircraft.
Beyond airplanes, the author expands the discussion to encompass other moving sound sources, illustrating the universality of the Doppler effect. Examples such as passing cars with blaring horns are used to further solidify the reader's understanding of the concept. The author meticulously details how the same principles of wave compression and expansion apply in these situations, resulting in the characteristic rise and fall in pitch. The post, therefore, provides a comprehensive and accessible explanation of the Doppler effect, demonstrating its relevance not only in specialized scientific fields but also in the everyday soundscape that surrounds us. It uses clear language and relatable examples to demystify a complex physical phenomenon, making it readily understandable for a broad audience.
Summary of Comments ( 32 )
https://news.ycombinator.com/item?id=43713524
Hacker News users discuss various aspects of the "whoosh" sound phenomenon. Several commenters offer additional examples of sounds exhibiting similar characteristics, such as the Doppler shift observed with passing cars or the sound of a large truck passing a house. Some discuss the physics behind the phenomenon, including the role of air pressure changes and the shape of the object creating the sound. Others delve into the subjective experience of these sounds, noting how perception can be influenced by factors like background noise and individual sensitivity. One compelling comment highlights the prevalence of this effect in movies and its potential exaggeration for dramatic effect. Another interesting observation is the comparison to the "sonic boom" of a supersonic aircraft, contrasting the continuous whoosh with the sharp crack of the boom. Finally, a few commenters mention the psychological impact of these sounds, including their potential to be unsettling or even anxiety-inducing.
The Hacker News post titled "Passing planes and other whoosh sounds," linking to an article on windytan.com about the physics of whooshing sounds, has generated a modest discussion with several interesting comments.
One commenter shares a personal anecdote about experiencing the Doppler effect with the sound of a passing plane, noting the distinct drop in pitch as the plane moves away. They also connect this experience to the sound of cars passing by, highlighting the commonality of the phenomenon in everyday life.
Another commenter delves into the specifics of the Doppler effect, explaining how the frequency shift is dependent on the relative velocity between the source and the observer. They then raise the question of why the sound of a passing plane seems to "whoosh" down rather than up, even though both rising and falling frequencies are involved. They hypothesize that this perceived downward shift is due to the greater change in frequency occurring as the plane moves away, alongside the general decrease in loudness as the source recedes.
A subsequent comment builds on this hypothesis, suggesting that the human ear is more sensitive to downward frequency changes and that the decreasing volume of the receding sound source might contribute to the perception of a downward whoosh.
Another commenter links to a Wikipedia page about the sonic boom, a different phenomenon associated with supersonic aircraft, distinguishing it from the Doppler effect discussed in the original article. This comment helps clarify the different types of sounds generated by moving aircraft and their underlying physical principles.
One user mentions their experience with sailplanes, explaining how the quiet nature of these aircraft allows for a clearer perception of the Doppler shift and a more pronounced "whoosh." This adds another real-world example to the discussion and highlights how the surrounding environment can influence the perception of these sounds.
Finally, a commenter with a background in audio engineering provides a more technical explanation, mentioning how the perceived pitch of complex sounds like those produced by aircraft engines is not solely determined by the fundamental frequency but also influenced by overtones and harmonics. They suggest that the Doppler effect's influence on these different frequency components might contribute to the complex nature of the perceived "whoosh."
In summary, the comments on the Hacker News post provide a range of perspectives on the physics and perception of whooshing sounds, from personal anecdotes to detailed explanations and related phenomena, demonstrating a shared curiosity about the acoustic world around us.