MadSci Network: Physics

Re: Why does sound travel and cover larger area in the night than in the day?

Date: Mon Jun 2 10:19:44 2003
Posted By: Aurelio Ramos, Grad student, Computer Engineering
Area of science: Physics
ID: 1051973294.Ph

Sound travels just as far during the night as it does during the day, 
since the only one thing that can affect sound transmission is the 
composition of the medium... In this case, the medium is air, and the 
composition of air does not change between night and day in any way that 
would signifficantly change the way sound travels...

However, you have made an observation about how sound travels at night, 
and indeed, you can hear distant sounds more clearly during the night 
than during the day... But why is that?

The human ear becomes less sensitive to weak sounds in the prescence of 
louder sounds. This phenomenon is called masking. During the day, the 
ambient noise level tends to be higher, because there are cars driving on 
the streets, people walking by, doors opening and closing, birds flapping 
their wings and singing, and so on. The prescense of all this sounds 
during the day makes it hard to hear faint distant sounds, not because 
their waves cannot travel as far, the waves travel just as far, but our 
sensitivity to those sounds is impaired by the masking phenomenon. We 
could say that the ambient noise "masks" your friend shouting in the 

During the night, everyone is asleep, very few, almost no cars at all can 
be seen driving by, most birds are asleep too, and it is generally more 
quiet. Since it is so quiet, its also easy to hear a faint distant sound 
very easily.

This difference between night and day can also seem to make echoes 
louder. And again, echoes are not louder at night than during the day, 
but, since echoes are distant and faint, just like any distant faint 
sound, they are also masked away by louder ambient noise.

This important example shows us how an observation such as yours can be 
very true: You can in fact hear distant sounds more clearly at night, but 
the mechanism responsible for this observation can be very different from 
what we expect.

Your mad scientist, 

Aurelio R. Ramos

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