MadSci Network: Physics

Re: Why won't the quack of a duck echo?

Date: Wed Apr 1 16:29:06 1998
Posted By: John Christie, Faculty, School of Chemistry, La Trobe University, Bundoora, Victoria, Australia
Area of science: Physics
ID: 891392577.Ph

I think the most likely explanation is that the radio report you heard came 
on a day early: it must have been intended as an April Fools prank!

I have definitely myself heard a duck's quack echo.

The radio report is quite implausible anyway. Firstly there are a few 
hundred different species of duck around the world, and at least that many 
different species of quack. Does the report mean that all of this variety 
of noises will not echo, while the croak of a frog, or a squeak on a 
clarinet (both of which can be more like ducks' quacks than quacks are like 
one another) will echo?

Echoing is caused simply by the reflection of sound waves off a hard 
surface. How good an echo is depends on the hardness and shape of the 
reflecting wall, and on the frequency spectrum of the sound. Usually higher 
frequency sounds reflect better (which is why the echo of a voice often 
sounds more like a whisper -- a voice without the low frequency 
components). It could be that a duck's quack is a noise that does not have 
a lot of high frequency components, and so does not reflect particularly 
well. It could be that the frequency spectrum is changed when the duck's 
quack echoes so that the echo does not sound much like a quack. I would 
believe that the echo of a duck's quack is much fainter than, say, the echo 
of a whip crack or a rifle shot. But I know that duck's quacks, like any 
other sound, can and do echo.

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