I’ve noticed an odd phenomena at my place on still, quite nights.
When the electric train are accelerating away from the local station at Robina – I can see them quite clearly through the gaps in the trees – there is a period of about five seconds or so where I can also quite clearly hear the train under power as it picks up speed.
I’ve had a look on Google Earth and the tracks are 3.2 kilometres away. A rough guess as to where the train is by the time the sound gets to me has the tracks curving around a bit with my place somewhere around the centre point of that curve.

Would I be right in guessing that somehow the tracks are acting as a kind of speaker as the train & its motor rumble & vibrate away on them to roughly focus the sound here? It’s louder even than loud trucks on the highway, which is just over half the distance that the train tracks are. I figured that people closer to the tracks would be hit by a heck of a lot more sound (inverse-square rule) because they would be outside the focal point of the track curve and also ‘see’ less overall track.

Time for bed, catch any answers later.

I’ve lived or alongside the railway tracks for years, mostly for good access to public transport. We use similar trains to what you use in Brisbania. The sound of them just seems to carry for km, far above the sound of traffic. maybe the higher pitch sound carries further, I’m not sure.

On a still night I can hear trains approaching and leaving the local station from a fair distance away.

Are you on the track?

Sound will travel through the rail much faster than it will through air: about 18 times faster.

probably mostly is still, dense air of fairly equal density (temp too) between source and listener, but if the entire side of the train is perpendicular and an arc there maybe some points/location at which there is some focus, as the train is likely to cause some directionality to the air vibrations/noise it generates.

Probably some atmospheric effects (temp gradients) can tend sound down more horizontal, as can being downwind.

There maybe some angles from the train that tend optimal refraction from air pressure gradients.

Are the tracks higher up or on a flat surface, any hills around?

when I was a child my grandparents lived in an old railway workers cottage situated perhaps 100m plus from the tracks

the 125 mph train was operating by then

well before the train arrived you’d hear the track hum in expectation of the train due to the power of the thing as it rumbled down the track, caused some vibration that would translate to sound coming off the track

the train would then roar by first the roar of the pulling loco then you’d hear the carriages then another roar of the pushing loco

they pulled the cottage down in the end and it became part of a supermarket carpark

in those days you could lay down in the middle of the road without any fear of any vehicle , sunday trading laws made the streets as quiet as a mouse, of course there weren’t as many people in London so it was still relatively liveable.

I’m wondering if this is relevant …

“On a clear night, a thermocline forms when the Earth cools, the lens effect funnels sound to you from cars, trains, and aircraft located tens of kilometers away. Everyone has heard the unmistakable and confusing sounds from trains that are known to be normally too distant to hear. During my childhood in Melbourne, I clearly remember hearing the sound of aircraft taking off from Tullamarine Airport that was located over twenty kilometers away.” – Richard de Crespigny

http://qf32.aero/2013/04/15/physics-for-the-coffee-table-quiz-6-2/

dv said:

Are you on the track?

No, as mentioned 3.2 km away from it, roughly perpendicular.

CrazyNeutrino said:

Are the tracks higher up or on a flat surface, any hills around?

The tracks are on the flats, we are up about 50 metres or so I think.

Spiny Norman said:

A rough guess as to where the train is by the time the sound gets to me has the tracks curving around a bit with my place somewhere around the centre point of that curve.

Would I be right in guessing that somehow the tracks are acting as a kind of speaker as the train & its motor rumble & vibrate away on them to roughly focus the sound here?

I would guess not the tracks but rather the side of the trains carriages, as it curves round the bend in the track, are forming a concave surface which reflects the noise of the train towards the centre point of that curve.

CrazyNeutrino said:

Are the tracks higher up or on a flat surface, any hills around?

Spiny lives in the hills, the tracks are on flat ground.

esselte said:

Spiny Norman said:

A rough guess as to where the train is by the time the sound gets to me has the tracks curving around a bit with my place somewhere around the centre point of that curve.

Would I be right in guessing that somehow the tracks are acting as a kind of speaker as the train & its motor rumble & vibrate away on them to roughly focus the sound here?

I would guess not the tracks but rather the side of the trains carriages, as it curves round the bend in the track, are forming a concave surface which reflects the noise of the train towards the centre point of that curve.

A gentle breeze on a calm night will carry sound vast distances. Something you would not notice in a city or large town along with all the other noises.

When I were a lad, we used to sit on the verandah after work. It was quiet. So quiet that you could not only hear your own heartbeat, but you could also hear the rush of blood in your own head. We could hear the train going by. It was 23km away. A low rumble in the distance.

Kingy said:

When I were a lad, we used to sit on the verandah after work. It was quiet. So quiet that you could not only hear your own heartbeat, but you could also hear the rush of blood in your own head. We could hear the train going by. It was 23km away. A low rumble in the distance.

the indian pacific passes 300m behind our place,love the sound as itgoes past :)