Often I will hear an intermittent, low frequency, powerful, booming sound that resolves into that of an airliner flying enroute high (FL 300+) overhead. So the first sounds that an airliner flying overhead to be heard are those. Why? I assume it has to do with the atmospheric conditions and how sound waves of different frequencies propagate forward..
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$\begingroup$ Related answer to Why is a Lockheed MC-130J Commando II creating such a loud droning sound? $\endgroup$ – Bianfable Nov 10 '19 at 16:29
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$\begingroup$ At some locations like Point Of The Mountain near Salt Lake City an airliner is typically heard as a very abruptly-starting loud whine rapidly descending in pitch. Is your location mountainous or flat? $\endgroup$ – quiet flyer Nov 10 '19 at 20:33
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$\begingroup$ Related: What makes the swooping noise when a jet flies overhead? $\endgroup$ – fooot♦ Nov 11 '19 at 21:50
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$\begingroup$ @quiet flyer I first noticed it in northern NH, then sometimes in southern NH also. $\endgroup$ – Don Slowik Nov 12 '19 at 14:12
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The air attenuates high frequencies more than it does low. Thus, lower frequency sounds travel farther, so you hear them first. Also, longer wavelengths will appear to "bend" around obstacles more than ones with shorter wavelengths, so buildings around you will in many cases develop acoustic "shadow" zones for higher frequencies as those buildings' dimensions are significantly larger than their wavelengths.
answered Nov 11 '19 at 5:12
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$\begingroup$ I think there's also an effect where sound is deflected upwards due to temperature gradients, and high frequencies are affected more than low. $\endgroup$ – Robin Bennett Nov 11 '19 at 14:44
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Low frequencies are attenuated less over distance and by obstacles. The lower frequencies, even from the music from a dance hall or band, or that car near you playing loud music will be heard first. It may be all you hear! It is also common that as we get older, and especially those in aviation, we become high tone deaf!!
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If you live in the approach path to a big airport, then there will be thumps and muffled booms as the landing gear is extended. It could be this that you are hearing.
answered Nov 10 '19 at 20:21
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$\begingroup$ Yes, I've heard those. I edited my OP to clarify that I'm referring to an airliner cruising up high. $\endgroup$ – Don Slowik Nov 12 '19 at 14:20
