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In a nutshell: Noise

Dear reader, your ears are astonishing. They have a subtle sensitivity that is beyond the skills of modern science to duplicate. And they’re kinda cute, too. Millions of years of selective honing has produced an exceptionally capable system: consider what an extraordinary and useful skill it is to be able to tell when a politician is lying to you, even with your eyes shut.

Boffins try to deal with sound by analysing it as changes in air pressure (decibels), which turns out to be a rather crude system. Using decibels to describe sound is like trying to describe the ocean by measuring the height of the waves: it’s definitely true and informative, but it’s a long way from being the whole picture. Unfortunately, ‘we are where we are’ as the pointless phrase has it, so let’s have a closer look at these clumsy decibels.

The way decibels are counted is a bit bonkers. Zero decibels (0 dB) is not silence. No, zero decibels is the softest sound a person with normal hearing can hear at least 50% of the time.

Worse still, decibels are measured on what is called a logarithmic scale. This means that if a sound is increased by 10 decibels, it actually doubles in loudness as we perceive it – it sounds twice as loud to us. If a sound is decreased by 10 decibels, it seems as if the volume has been halved.

You couldn’t make it up.

Here are all the examples of decibel levels of everyday sounds that I could find, to give you a feel for how the scale works:

0 dB Threshold of hearing
10 dB Rustle of leaves
20 dB Water dripping
30 dB Soft whisper
40 dB Quiet radio in room, refrigerator
50 dB Normal conversation, moderate rainfall, light traffic
55 dB Quiet suburban neighborhood
60 dB Conversation
70 dB Noisy restaurant, busy traffic
75 dB Dishwasher, washing machine, vacuum cleaner
80 dB Alarm clock, blow dryer
85 dB Electric razor
90 dB Roar of sports crowd, lawn mower
100 dB Snowmobile, chainsaw, power tools
102 dB Leaf blower
110 dB Stereo headset, rock music
115 dB Subway train screech
120 dB Rock concert, thunderclap
130 dB .22 caliber rifle
140 dB Toy cap gun, firecracker, low flying aircraft, jet take-off
170 dB High-powered shotgun
180 dB Rocket launch

Around the 70 dB mark is the boundary between things that you might think of as quiet, and those that are loud. The logarithmic scale has the result that as the numbers increase over 70 dB, things start getting a lot louder.

Coming soon (as if you hadn’t guessed): the harm that noise can cause, and the noise from planes.

Check Also

Public consultation starts on Manston’s night flying proposal

Runs until Friday 2 March 2012

Thanet District Council is now asking members of the public for their views on proposals for regular night-time flying at Manston Airport. The proposals were submitted by Infratil, owners of the airport, on 27 October 2011 and included an aircraft noise assessment report and economic assessment, which are technical reports explaining the implications of the proposal.