From: pauld@exploratorium.edu
Date: Sun Sep 14 2003 - 11:13:01 PDT
Message-ID: <1227.209.239.173.234.1063563181.squirrel@www.exo.net> Date: Sun, 14 Sep 2003 11:13:01 -0700 (PDT) Subject: echo of a quack From: pauld@exploratorium.edu
Hello Pinholers
I long suspected that the scientific legend that a duck's quack has no
echo was an urban legend.
It turns out that acoustics scientist Prof. Trevor Cox recorded a duck
quack in an anechoic chamber, in an echo chamber, and next to a cliff.
You can hear the recordings at
http://news.bbc.co.uk/media/audio/39309000/rm/_39309986_rev_duck.ram
You can see why the legend arose, for any reasonably distant cliff, the
echo returns while the duck is still making the quack. Listen carefully to
the cliff face recording and you can hear the echo overlaid on the
original quack.
Paul D
Here is a selection from the text of the BBC article.
The old saying that a duck's quack produces no echo is...
well, just plain quackers.
Acoustics expert Professor
Trevor Cox has deployed the
most powerful techniques his
science can muster to prove
the bird's calls will bounce off
hard surfaces in just the same
way as all sounds.
But the researcher has
discovered there is a kernel of
truth in the myth which may
explain how it arose in the first
place.
He says the way a duck quacks, with a long
"aaaacckkk" on
the end of the call, tends to mask any echoes that are
produced.
Waddle waveform
It might seem a bit bizarre that scientists should
go to all the
trouble of investigating quacking ducks, but
Professor Cox is
an expert in controlling echoes.
His work helps building designers improve the
acoustics of
concert halls, cinemas, and even railway stations
where
echoes can make it difficult to hear the original
sound source
- such as the tannoy making a train announcement.
If ducks had some secret trick, he would certainly
want to
know about it. "Many people think the duck's quack
having no
echo is true so we thought we would investigate
it," he told
the BBC.
"It's a bit of fun but it does demonstrate what we
can do."
So, waddle forward Daisy the duck.
Cox and colleagues at Salford
University's Acoustics
Research Centre put the
feathered animal in an
anechoic chamber, which
deadens all echoes, and also in
a reverberation chamber, to
produce as much reflected
sound as possible.
They then used powerful
computer tools to analyse
Daisy's noises and to simulate
them in different environments - such as in front
of a cliff
face.
"What all this shows is that the duck's quack fades
away; it
sounds like it quacks for a long time.
"Because the duck's quack is rather quiet anyway
and the
echo comes on the back of a fading sound field, it
is as if the
echo is being masked. You just don't hear the echo
very well
and that's probably how the myth arose."
http://news.bbc.co.uk/media/audio/39309000/rm/_39309986_rev_duck.ram
This archive was generated by hypermail 2.1.3 : Mon Aug 02 2004 - 12:05:31 PDT