Neat writeup! From the title, I had my fingers crossed that they integrated ADS-B flight tracking data to show a map of where the sound of airplanes in the air is currently observable.<p>If anyone wants to go down that rabbit hole really far, I'm imagining general profiles of the sound each airplane makes, considering altitude, different sound propagation by frequency depending on distance the sound travels, and geography. Might as well throw air properties in too, to minimize the overall error. The user could provide their location and see the estimated arrival time
and frequency of the sound from the airplanes in the sky.
It’s quite common in research to plot the aircraft noise footprint. It looks like this:<p><a href="http://2.bp.blogspot.com/_3cvpfoj7mb8/TJpQu-_IqfI/AAAAAAAAC7w/hoJ0ZkoVoDo/s1600/noisecomparison3.jpg" rel="nofollow">http://2.bp.blogspot.com/_3cvpfoj7mb8/TJpQu-_IqfI/AAAAAAAAC7...</a><p>A significant part of the noise signature is from the jet of hot turbulent air shearing against the surrounding cool air. This happens behind the aircraft. The Doppler effect plays a role too but for jet aircraft the noise is generated behind the aircraft and much is projected backwards. A lot of work has gone into geometries to reduce this shear noise.
I was in the boondocks last week and had a striking example of a jet climbing up to its ceiling around 2 or 3 miles away. I tried to figure out the answer to this in my head and didn't get anywhere - was hoping a kind geek would come up with something.
I happen to write control and processing software for wind tunnel experiments.
I am currently working on an acoustic setup. I believe things like wind speed I influence the delay too, as it affects the distance the sound has to travel between the source and you.
Nice, but very wrong. This describes the case of a plane suddenly appearing in mid-air and starting to make noise, something, planes rarely do (maybe in the Bermuda triangle). It's like thunder after lightning, or seeing a ball fly before hearing it being kicked when you're far away.<p>The aircraft, however, is flying <i>for a long time</i>, certainly it was flying and making noise much earlier than when it is passing the observer. As long as it flies subsonically, i.e. sound outpaces the aircraft - which is the case for every single commercial plane - the sound may be able to reach you much much earlier than the plane: As an example, take an aircraft flying with 100 m/s directly towards you. With every second flying, the sound will gain another 200 m distance relative to the aircraft (speed of sound ~300 m/s).<p>If you're 100km away, the aircraft will reach you after 1000s, the sound has reached you after 333s, i.e. <i>ahead</i> of the aircraft. If you're 200km away, the aircraft will reach you after 2000s and the sound has reached you after 667s.<p>So, how come it sounds like the sound of the plane is <i>behind</i> the plane? It's got to do with sound attenuation in the atmosphere and your hearing threshold.<p>So, it's not at all like in the article.<p>Somewhat minor nitpicks:<p>- The aircraft is drawn to essentially fly with Mach 1, i.e. at the speed of sound, as the position of the plane relative to the wave does not linearly increase with time. Essentially all airplanes you see are flying subsonically (unless you're in the military).<p>- "If the plane was moving very slowly, it wouldn’t outpace its sound by much." That's completely wrong. "very slow" aircraft are much slower than their sound, and all commercial aircraft still are slower than their sound, all of them are outpaced by their sound rather than the other way around.<p>[Edit: typos & math]