Testing Noise (2001)
In noisy environments, microphones are used to measure sounds levels. But who measures the microphones?
[Music plays and the words flash around the screen and resolve into the title “sci files”]
[Image changes to construction vehicles on a building site, heavy traffic on roads, suburban trains and aircraft landing on runways]
Narrator: The clatter, boom, crash and roar of city life for most of us, is just background noise. But to those who live on busy roads, near constructions sites, or under flight paths, it’s sometimes simply unbearable and complaints end up in court. But the judge needs to know if the noise was just a nuisance or legally unacceptable, so the noise needs to be monitored.
[Image changes to microphone mounted on pole on a buildings roof]
Some authorities have permanent noise monitors in place, like this one near Sydney airport. The microphone’s measurements have to be absolutely correct. And Australia’s science agency, CSIRO, makes sure that they are.
[Image changes to Dr Meldrum in a laboratory opening a case to remove a microphone and then setting it up in a specially soundproofed room]
The microphone is placed in what’s called an anechoic chamber or echo free chamber then subjected to a series of sounds.
[Image changes to Dr Meldrum demonstrating with microphone in chamber]
Dr Bruce Meldrum: When we’re testing this device we need to have sound, which is coming from one direction only and it’s coming from the source towards this microphone and the microphone is picking it up.
[Image changes to view of microphone pointing at loud speaker in chamber]
Narrator: The sounds begin at a very low frequency, before increasing to a glass shattering pitch above most hearing. [Image changes to view of audio waveform on oscilloscope]
[Image changes to Dr Meldrum]
Dr Bruce Meldrum: The importance of what we do, is to reassure the customer, in this case it’s the airport noise monitoring authorities, that the microphones that they’re using respond correctly to all of the frequencies. That they are not faulty and that they’re performance is adequate to their specifications.
Narrator: It won’t stop the noise… but it does provide a sound basis to help manage an increasingly noisier world.
[Image changes to heavy traffic on roads, suburban trains and aircraft taking off from an airport]
[Music plays and the words “sci files” appears on the screen]