What it shows
Sound level is measured in decibels, a scale where every 10 decibels sounds about twice as loud. Measuring at the same spots at different times of day gives a noise map that shows where and when levels pass the limits set for residential and silence zones.
The science
The decibel scale is logarithmic: 60 dB is ten times the sound energy of 50 dB and sounds roughly twice as loud. A quiet room is about 40 dB, normal talk 60, a busy road 80, and a loud horn close by over 100. Long exposure above about 85 dB damages hearing. Indian limits are 55 dB by day and 45 by night for residential areas and 50 by day and 40 by night for silence zones round schools and hospitals, so a survey can show which places are over the limit.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A smartphone with a free sound level meter app
- A printed map or hand-drawn sketch of the area
- A notebook with columns for place, time, reading and main sound
- Coloured pencils for the map
Safety
For this project: Measure from the footpath with an adult near busy roads; never stand on the road to take a reading.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Choose eight spots: a main road, a lane, a school gate, a market, a park, a temple or mosque, a home room and a bus stop.
Draw a simple map of the area and mark the eight spots on it with numbers.
Set the app to show the average level and hold the phone at chest height away from your body.
At each spot take a 30 second reading in the morning, at midday and in the evening, on two different days.
Note the main sound each time: traffic, horns, loudspeakers, people, machines.
Average the readings for each spot and time.
Colour each spot on the map: green under 55 dB, yellow 55 to 70, red above 70.
Compare each reading with the limit for its zone type and list the spots that exceed it.
What you should see
A coloured map with the road and market in red at most times and the park and home in green, and a list of places that exceed the legal limit, usually the school gate during rush hour.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What does 10 decibels more mean?
About twice as loud, and ten times the sound energy.
2What is the daytime limit for a residential area?
55 decibels.
3Above what level does long exposure damage hearing?
About 85 decibels.
4Name two ways to cut noise near a school.
No-horn signs and trees or walls that block the sound.
Take it further
Measure before and after a festival night and compare the levels.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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