You will hear a lecture about the study and design of sound in cities.
First, you have some time to look at questions 31 to 40.
Now listen carefully and answer questions 31 to 40.
This lecture looks at acoustics, the science of sound in urban settings such as cities.
As an acoustic engineer, I believe this field is likely to change considerably.
Earlier research into city soundscapes was quite basic.
We recorded sound levels in decibels.
I might take a meter to a particular location, measure the noise, and then ask a group of people at what point they found it irritating.
Information of this kind allowed acoustic engineers to produce what are known as noise maps, showing the sound environment.
In reality though, these maps have limited value.
They reveal that roads generally have the greatest noise levels, which is hardly unexpected.
They miss a great deal because they cannot represent the complicated changes in sound over time.
For example, they leave out noise coming through neighbours' open windows, or from neighbours spending time in their gardens, which can be quite noticeable in summer.
No database records that kind of information.
The maps also fail to reflect individual differences in the way noise is perceived.
Someone like me, after years in acoustics, may react very differently from someone without that experience.
Even so, these fairly rough maps have helped by supplying information and making the public aware that noise needs attention.
In other words, it is a political issue.
That recognition matters because rules and regulations are needed.
Noise can produce a range of harmful effects.
People who live in cities know that activity continues around the clock, so disturbed sleep is common.
We also know that noise can raise stress levels through physical changes that affect the blood.
There are further consequences.
If school children lack a quiet place to study, the quality of their work is likely to decline.
A further weakness of measuring decibels is that the figure does not distinguish one kind of noise from another.
Sounds that many people regard as pleasant and calming may still register quite high readings.
Consider, for example, a fountain in a town square.
We would not necessarily want to limit or remove that sound.
Researchers may therefore need to take such sounds into account in urban design.
But decibel readings alone cannot do this.
Instead, many investigators are adopting methods from the social sciences, including questionnaires that explore people's emotional reactions to sound.
So what would people actually like to hear in a city?
Recent research involving several disciplines has produced findings that initially appear inconsistent.
Urban areas need a feeling of activity.
They should be lively, with noises such as heels clicking on paving or steam hissing from a coffee machine.
At the same time, those sounds must not become intrusive because people also need opportunities to unwind.
A major obstacle will be persuading architects and town planners to apply this research.
Beyond a basic introduction to acoustics, they receive very little training in the subject.
They should view sound as a way of enriching urban life.
At present, however, they often treat it as something to eliminate or minimise, or as an engineering responsibility comparable to street drainage.
City noise needs to be understood as an aesthetic feature, possessing qualities associated with an art form.
Once we accept that, we must investigate what shapes it and how designers can use it.
This calls for a sophisticated understanding of several factors.
How does sound relate to culture?
What can psychology tell us about its interaction with human development and social relationships, and about its influence on thoughts and feelings?
Can physics help us understand the nature of sound itself?
Modern technology may also assist.
Architects and planners already use virtual reality programs to communicate their ideas and demonstrate the likely effect of proposed buildings.
The current problem is that these programs are silent.
In future, realistic audio could be added, allowing soundscapes to be tested before construction.
With the best available technology, the future city may be as satisfying to hear as it is to see.
