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Old 02-08-2019, 03:29 AM   #1
xoxoxoBruce
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Sound Travels

My buddy was down here gathering firewood left behind by the new sewer line they ran through my property. A neighbor stopped to talk to him and told him he and his wife really enjoyed when I had the band rehearsing here. They would mix drinks and sit outside grooving on the tunes. News to me.

When we make noise, loud party or tuning an engine, we usually try to take neighbors into consideration, especially in late or early hours. But it's hard to figure how far and how much of the sound travels. It gets attenuated by distance, building, foliage, etc. Because there is no neighbors there we don't think about up.

I came across this today...

Quote:
Glaisher wrote on his memoirs of balloon flight, Travels in the Air:
I find that the intensity of various sounds emitted at the surface of the earth is carried up to very great heights in the atmosphere. The whistle of a locomotive rises to near 10,000 feet, the noise of a railway train to 8,200 feet, the barking of a dog to 5,900 feet; the report of a musket is heard to about the same height; the shouting of men and women can be heard sometimes as high as 5,000 feet, and at this altitude the crowing of a cock and the sound of a church bell are audible.

At a height of 4,550 feet the roll of a drum and the music of an orchestra are distinctly heard. At 3,255 feet in altitude, a man's voice may make itself heard; the rolling of a cart on the pavement can be distinguished somewhat higher; and in the stillness of the night the course of a river, or even that of a small stream, produces at this elevation almost the effect of a high waterfall. At a height of 3,000 feet the croaking of frogs in a morass is heard in all its intensity, and even the sharp note of the mole-cricket is distinguished easily at an altitude of 2,500 feet.

What Glaisher and his companions experienced was the effect of humidity on sound level. It has been observed that as humidity increases the sound level also rises. Clouds and fog being more humid “collects sound with such intensity,” explains Glaisher, “that whenever, in passing through a cloud, we have heard a band playing in a town beneath us, the music always seemed to be close at hand.”
“Lower humidity absorbs more sound, especially at higher frequencies, because of "molecular relaxation" in the gases in the air (a level of 10% humidity absorbs the most),” explains NPS. “A substantial change in atmospheric pressure, equivalent to thousands of feet of elevation gain, has a small influence on noise level for most sources, but substantially affects the received levels of those sounds.”
Sound carries better in humid air? I'd have thought it was the other way round. Mother Nature is sneaky.
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Old 02-08-2019, 12:33 PM   #2
Gravdigr
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I can remember being at Grandmadigr's and hearing the train (not the horn, which of course we also heard, but the train itself passing over the tracks) after a storm.

The closest a track gets to her house is nine+ miles.
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Old 02-08-2019, 01:27 PM   #3
glatt
 
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One time I was in my backyard in Lewiston ME and heard racing engines in the distance. It sounded like they were going around a track the way the doppler shifting was happening. I didn't know of any racetracks nearby, but I knew there was a place they advertised on TV called Oxford Plains Speedway. No idea where it was, but it wasn't near me. I went inside and got a map, looked it up, and the sound was coming from exactly that direction.

Google Earth tells me it's 14.35 miles from the center of the speedway to my childhood backyard.
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Old 02-08-2019, 01:30 PM   #4
glatt
 
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Oh, and regarding the original post, I got a ride above my hometown in a hot air balloon. It was amazing what you could hear from up there and you floated silently by. Tons and tons of dogs barking at you, but also people on the ground talking about you to one another as you float by.
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