[HN Gopher] Passing planes and other whoosh sounds
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Passing planes and other whoosh sounds
Author : zdw
Score : 178 points
Date : 2025-04-17 05:53 UTC (17 hours ago)
(HTM) web link (www.windytan.com)
(TXT) w3m dump (www.windytan.com)
| Toutouxc wrote:
| Thanks, now I'll be hearing and thinking about the effect for the
| rest of my life.
| shmeeed wrote:
| I've been hearing and thinking (occasionally) about this effect
| for years, so this explanation is very welcome.
| maciejb wrote:
| Next time I see a plane coming, I'm going to lie on the floor to
| see if the whoosh sound does it fact change.
| djmips wrote:
| Check out his video. It's educational!
| https://www.youtube.com/watch?v=Amj4UevyRfU
| netsharc wrote:
| She's a woman, btw.
| djmips wrote:
| My apologies.
| normie3000 wrote:
| > it's like the pitch goes down at first, but when the plane has
| passed us, the pitch goes up again. That's not how Doppler works!
|
| Call me a dummy, but this was exactly how I thought Doppler
| works.
| shmeeed wrote:
| Let's say the mistake is understandable, because it happens to
| coincide with the observation of a passing jet. ;) I guess
| that's why Doppler explanations nearly always use an ambulance
| as their example.
| potato3732842 wrote:
| The jet example will needlessly confuse people and create
| fodder for low effort "akshually" type commentary because the
| air getting sucked into the front and crammed out the back of
| the engine sound very different so you can get like most the
| same effect without the aircraft actually moving relative to
| the observer.
|
| People explaining doppler don't want to have to explain this
| to a bunch of nit pickers, so they use an ambulance.
| beardyw wrote:
| As a sound comes towards you (say an ambulance) the sound waves
| arrive squashed (higher pitch) and as it goes away the sound
| waves are stretched (lower pitch).
| shmeeed wrote:
| I'm just armchair musing here, and I'm definitely no expert on
| sound waves, but I wonder if they considered the fact that most
| airliners have more than one engine. Could the effect also be the
| superposition of multiple engine sounds?
|
| Those have a fixed spatial distance, too, and the effect would (I
| suppose) change with the lateral angle to the listener during the
| fly-by. This theory should be pretty easy to falsify, because
| then the effect would not occur if the plane's path went exactly
| overhead.
| nicemountain wrote:
| For that, the pressure waves (sound) coming from the engines
| would have to be somewhat coherent, or correlated in phase.
| Since what we're hearing is essentially turbulence, that's not
| going to be the case.
| jeffbee wrote:
| Engines in modern aircraft are phase-locked, though.
| mrob wrote:
| The majority of the engine noise is caused by the turbulent
| mixing of the exhaust with the surrounding air. Turbulence
| is chaotic, so even if the engines are phase locked the
| sound rapidly becomes incoherent.
| Toutouxc wrote:
| Do you have a source for that? I've heard about something
| that some twin-props have, but definitely not jets. The
| engines don't even run at the same RPM.
| jeffbee wrote:
| https://www.osti.gov/biblio/6356085
|
| It is what the "Sync" switch on the panel does.
| Toutouxc wrote:
| Yes, but it seems like no turbofan synchrophaser systems
| have been implemented yet. Only on turboprops.
|
| https://aviation.stackexchange.com/questions/71738/is-
| engine...
| roygbiv2 wrote:
| We have planes pass overhead at about 6000ft. When the conditions
| are right they'll make a completely different sound, I've always
| assumed it's the Doppler effect mixed with the valley we live in
| but I'm always very curious when it does happen.
|
| They make their usual sound but then there's a second sound that
| arrives, a lot higher pitched. Sounds like they've struck it in
| reverse or something (they haven't they're just doing a normal
| decent).
| oe wrote:
| I think it's some engine type that makes the sound at some
| specific speed / throttle setting. But I can't remember the
| specifics. Some planes passing us make the sound, most don't.
| philipwhiuk wrote:
| Sound is also reflected off a cloud layer if present.
| smcameron wrote:
| Hm, I suppose that's why a flanger[1] (guitar effect pedal) can
| sound a little like a jet plane.
|
| [1] https://en.wikipedia.org/wiki/Flanging
| albert_e wrote:
| Tangentially related
|
| I once picked up my memory foam mattress and stood it up against
| one of the walls ... for cleaning the bed or whatever.
|
| As I walked past the mattress I instantly noticed that the
| mattress is such a good absorber of audio waves that I could
| immediately notice a dip in ambient sound in the ear facing the
| mattress.
|
| The room was already "silent" and this newly discovered lower
| limit of silence was pretty surprising to me physiologically.
| meindnoch wrote:
| Everyone should try a real anechoic chamber once. The silence
| there is _deafening_.
| BobbyTables2 wrote:
| I shudder to think what tinnitus would sound like in an
| anechoic chamber...
| ilikepi wrote:
| Probably similar to whatever its normal frequencies are for
| you, but perceptually louder. That seems to be my
| experience when I'm in a location with minimal background
| noise...
| larusso wrote:
| Don't know if this is the same but I went to Death Valley on
| the Devil's Golf Course during summer. There was no wind no
| nothing. It was so damn silent. Wonder how that compares to
| an anechoic chamber now.
| 0_____0 wrote:
| Having experienced both, it's very similar.
|
| Edit to add: I've been in an anechoic chamber and also the
| black rock desert, which is dead flat and thus has very
| little surface area oriented to reflect sound back at the
| listener, which makes it similar in that you don't
| experience environmental reflections.
|
| Devil's Golf Course has more "texture" to it but if you
| were quiet on a windless day I think the effect would be
| similar.
| cf100clunk wrote:
| If you are handy to an R&D lab that has a combo Faraday
| Cage/anechoic chamber you can have a nice experience free of
| RF and audio noise and stimulus. Even better if it is dimly
| lit in near-infrared. Even better-better if it has a tank of
| warm water with lots of epsom salts, although I've never been
| in a lab that had such a thing as a requirement.
| meindnoch wrote:
| I'm skeptical of shielding yourself from RF noise having
| any detectable effect.
|
| Unless you have amalgam tooth fillings, that anecdotally
| can act as a crude diode, and demodulate strong enough AM
| signals.
| cf100clunk wrote:
| The goal is not to prove or disprove any affects on one's
| physiology, but simply to have the experience of being
| free of RF and audio for the sake of it.
| stouset wrote:
| I think the point is that even saying the "experience" of
| being free of RF implies a perception which does not
| exist.
|
| Plus it's well-known that you don't _really_ get the full
| experience of this unless you manage to shield yourself
| from neutrinos by surrounding yourself with sufficiently-
| dense proto-neutron stars.
| cf100clunk wrote:
| Neutrinos, cosmic rays, and extraterrestrial subatomic
| particle streams are not considered RF, right?
| stouset wrote:
| If we're going out of our way to eliminate things that
| cause zero perceptual experience I don't see why you
| would exclude them.
| thefroh wrote:
| it's also the effect that lets you kinda know if you're near a
| wall (for example when you're fumbling around in the dark)
| junon wrote:
| Pretty sure this is also why, when you stand at the right spot in
| a techno concert, the music starts to sound like a jet engine.
|
| We also have this in game development, where if two sound effect
| emitters play the same effect at the same time with just a bit of
| offset, phase, whatever, they sound like that.
| meindnoch wrote:
| If the offset is fixed, the effect is called a comb filter. If
| the offset is changing, the effect is called flanging. The name
| stems from recording engineers rubbing their fingers against
| the _flange_ of a reel-to-reel recorder 's tape reel, to brake
| it slightly, which adds increasing delay to the sound.
| mrob wrote:
| The same effect is responsible for an unavoidable flaw with
| stereo loudspeakers, where you have differing path lengths
| between your ears and each speaker. Try playing some mono pink
| noise on stereo speakers and moving your head, then compare with
| the same sound hard-panned to a single speaker. It's most obvious
| when you're close to the speakers and in an acoustically dry
| environment. If you add lots of additional reflections you'll
| generate many overlapping interference patterns that will average
| out to a smoother frequency response. This is one reason why
| adding a real physical center channel can improve clarity of
| dialogue in movies.
| meindnoch wrote:
| Real hi-fi enthusiasts sit at the reference listening point of
| their system (the third corner of an equilateral triangle
| placed on the speakers). Everyone else won't notice the
| difference; they listen to 256kbps Spotify anyways.
| mrob wrote:
| It doesn't take much head movement to cause audible flanging.
| The real hi-fi enthusiasts will have to use head clamps like
| in A Clockwork Orange (or just use headphones).
| lavela wrote:
| So who is up for turning the last graph of the article into a
| synthesizer?
| PaulHoule wrote:
| How about the back and the front of the plane?
| m3047 wrote:
| Ground feature echo (mentioned in the article)... possible. Not
| mentioned here or in the article: thermocline in the atmosphere.
| Thermocline in the water is traditionally how submarines "hide"
| from surface ships.
|
| I hear flanging from the planes incoming from quite a distance,
| and they're pretty low when the fly over where I live. More
| telling: I can hear the freeway and the busy arterial, "depending
| on how the wind blows". Sometimes it flanges, too.
|
| So: ground reflection along with thermocline refraction seems a
| perfectly plausible explanation for one source of the phenomenon;
| could be several, probably all involving ground and atmospheric
| factors.
| arnarbi wrote:
| There was a pretty good video on this a couple of years ago:
| https://www.youtube.com/watch?v=QFv3QPNU6hw
| jszymborski wrote:
| Always a huge pleasure when Oona posts something. Her posts are
| the sort of magic you get when a genuinely curious person has the
| competence to satisfy and explore those idle curiosities. Glad
| she's still going strong after all these years.
| dredmorbius wrote:
| I strongly suspect that the unexpected doppler shift is from
| jetwash.
|
| That is, the principle source of noise from a jet aircraft isn't
| the engines directly (turbine spool), or the fuselage's passage
| through the air (turbulent white noise), but the stream of
| hugely-accelerated air which has exited the turbine(s) and is now
| shredding itself against the stationary surrounding air. The
| noise source therefor isn't a _point_ (engine) but a linear
| source (the turbulent shred-wall interface between the jetwash
| and surrounding air), and it is _moving rapidly backwards from
| the aircraft_.
|
| Which means that as the aircraft approaches you, the jetwash /
| shred turbulence is moving away from _you_ , and is doppler-
| shifted toward lower frequencies, and once the aircraft passes
| minimum distance, the jetwash is streaming _toward_ you, at a
| high fraction of the speed of sound, and should therefor be
| doppler-shifted _upwards_.
|
| The insight that it was jetwash and not engines themselves making
| noise became clear to me when I lived near an airport with a road
| passing immediately behind the runway. I happened to be cycling
| past one day as a jet lined up for take-off, heading away from
| me. I was positioned directly behind it (and out of immediate
| reach of the jetwash). My first thought as the engines spooled up
| was "this is going to be _loud_ " ... but it _wasn 't_. Rather
| than the roar you'd hear when you were _alongside_ the plane, all
| I heard was a loud spooling turbine whine ... until the jetwash
| roar itself returned to me echoed off mountains a few kilometers
| distant.
|
| TL;DR: Jet engines don't make (much) noise, their exhaust does,
| and it has a markedly different velocity vector than the plane
| itself, or its engines, accounting for a different doppler
| signature.
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