News in Science

Quacks Don't Echo

Never one to duck a tricky issue, Dr Karl ponders the myth that the sound of a quack can not produce an echo...

The world is full of unproven "facts". You'll hear them in a pub after a few drinks with some mates. You will probably read them in an email from a well-meaning friend within the first month of your getting onto the Net. Or sometimes, you'll hear them debated on talk-back radio.

In 2003, one of them was scientifically debunked at Salford University in northwest England, at the annual meeting of the British Association for the Advancement of Science. It was that old favourite, "A duck's quack doesn't echo, and nobody knows why."

This question came up a few years ago on my Science Talk Back show on the ABC's Triple J radio. My honest answer was that I really didn't know, because I hadn't read any research on the topic, but on the face of it, it sounded like a ridiculous claim for three reasons.

First, each of the many species of duck has its own different quack. In fact, to make it more complicated, there are gender differences in quacks. For example, the female mallard duck makes a loud honking quack, while the male mallard duck makes a softer, rasping quack.

Second, most species of duck like to hang around on the water - usually out in the open. There are not many hard reflective surfaces near most lakes, so you don't get many echoes, anyway.

Third, why should the quack of a duck (alone, of all sounds ever made on our planet) have some magical property that makes it echo-free?

Then a Triple J listener rang in with what the Intelligence Community calls "Ground Truth". His family owned a duck farm, and he assured me that the quack of their ducks most certainly did echo off the walls of the sheds.

And that's where our understanding with regard to Ducks' Quacks rested, until Professor Trevor Cox from the Acoustics Research Centre at the University of Salford reported his research with Daisy the Duck one September. There was nothing special about Daisy - he just rang the local farm until he found one (Stockley Farm) that would lend him a willing duck.

Professor Cox has worked with problems in sound for many years. For example, you've probably heard the sound from the loud speakers at a railway station echoing away until it's almost unrecognisable. Prof. Cox is the guy who can create a virtual prototype of a railway station inside a computer, and then adjust the design until you can hear the sound clearly. He can do the same for concert halls and even restaurants - you've probably had the difficulty of having to shout across the restaurant table just to be heard. And he's also worked on using trees to absorb the sound of traffic, or planes.

So he knew what to do with Daisy and her Quack.

First, he got her to quack in an anechoic chamber, which is a specially-designed room that deadens echoes. Her quack sounded like a regular quack, but a little softer than he expected.

Second, he then got Daisy to repeat her quack in a reverberation chamber, which artificially enhances the echoes. The quack did indeed echo - in fact, it sounded rather sinister.

Third, he used a computer to simulate her quack in a concert hall - and sure enough, there was a small echo. And the same happened when he simulated Daisy's quack as she flew in front of a virtual cliff inside his computer.

But he noticed two odd things. First, Daisy's quack didn't finish sharply (like a hand clap), but tailed off softly. It decayed or faded away gently and gradually. This means that it's hard to tell the difference between the original quack, and the echo. Second, her quack was actually quite soft, so the echo is even softer. These two factors mean that even if you do get an echo, it is lost in the tail end of the original quack.

Professor Cox is hoping to use this knowledge in improving echo-ridden environments, such as railway stations and restaurants. And I guess that the original myth about the sound of the duck's quack being echo-free is just quackers...

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