Science & Technology in Action

3rd Edition

Towards a Quieter City

Dublin City Council

Excessive noise can interfere with normal communication, cause general annoyance, disturb sleep and impair hearing. It is recognised as a serious problem in cities where the sound level is typically between 60 and 70 dB(A).
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Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

Cities are full of sound – from people, factories, music, alarms, cars, trams, trains, planes, construction, animals (though not as much as fifty years ago).

What is sound? When does sound become noise? Is there a quantifiable distinction between them or is ‘noise’ a purely subjective label? Does noise have an adverse effect on people? In this lesson we will try to clarify these and other questions. 

What is sound?
Our ears are able to detect rapid variations in air pressure as long as they are in the frequency range of about 16 Hz (hertz) to 16 kHz and their intensity is greater than one thousand millionth of atmospheric pressure. Because they are so sensitive our ears can be permanently damaged by very loud sounds.

What is noise?
The simple answer is that noise is unwanted sound. What characterisesnoise is more difficult to say but the following factors are significant: loudness and frequency range, whether it is continuous or intermittent, the time of day and whether it matches our mood or needs at the time. So what might otherwise qualify as pleasant music may become ‘noise’ if it interferes with our ability to work, communicate or relax.

In the centre of a city where there are generally more people and vehicles, noise levels are high. In built-up areas sound bounces off hard surfaces while along suburban and country roads the vegetation and soft ground absorb much of the sound.

True or False?

  1. Noise is audible sound. false
  2. The frequency of a note determines its pitch. true
  3. Traffic noise consists of one main audible frequency. false
  4. The loudness of a sound depends on its power density. true
  5. Sound is absorbed more by hard surfaces than by vegetation. false
  6. The rate at which energy is propagated is measured in watts. true
  7. One watt means one joule per second. true
  8. If the power density of a sound increases by a factor of ten then it is 3 dB louder on the decibel scale. false
  9. If the power density of a sound increases by a factor of ten, it is perceived as being about twice as loud. true
  10. If the power density of a sound increases by a factor of two then it is 3 dB louder on the decibel scale. true