Most recent answer: 07/23/2016
- Debbie (age 60)
Wadesboro, NC, US
Sounds don't really travel more downhill, so that's not the direct explanation. It's got to be that the shape of the hollow is in effect acting like a lens and/or mirror for the sound.
If you've ever been in an elliptical stadiium, you may have noticed that standing at one focus of the ellipse, you can clearly hear a friend speaking at the other focus, because the stadium acts like a mirror refocussing the sound.
Why is the effect more noticable at night? Maybe that's just because it's quieter at night so it's easier to hear voices. It could also be that there's a tempperature diffeence between the low spots and the high spots, which makes a sort of lens for the sound. Maybe that helps focus sounds from the top on the house at the bottom.
If the main effect is just the mirroring from the groud shape, it won't vary much from night to night. If it's mainly lensing from temperature differences, then it will depend on the weather.
By the way, there's a reciprocity theorem you should know about. If your friend stands at a spot where she can easily hear the neighbors, they can also easily hear her!
(published on 07/23/2016)