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1. Loud but clear

The decibel scale
What are decibels?
We measure the loudness of sounds using the decibel scale. The scale has to cover a huge range of levels. The quietest sound that we can hear is given a value of 0 decibels (dB). A pin dropping measures 10 dB and a soft whisper measures 20 dB. A jet aircraft, at 130 dB, is the loudest sound that we can hear for a short period of time without pain. This sound is actually a million million times more powerful than a pin dropping. However, we can fit it onto the decibel scale because of the way that the scale works.
dB Sound
0 threshold of hearing
10 pin dropping at 10 m
20 soft whisper
30 library
40 quiet conversation
50 normal conversation
60 a busy office
70 vacuum cleaner
80 inside a small car
90 lawn mower
100 large orchestra
110 rock music
120 boom stereo in car
130 earphones up loud/ jet plane
140 air raid siren
150 military rifle
Picture 7. The decibel scale. Pain starts at 130 dB and the bones in the ear may break at 150 dB.
How does the scale work?
The power is multiplied by ten for each ten decibels on the scale. So by the time you go up by 40 decibels, the power has been multiplied by ten four times (10 x 10 x 10 x 10). So it is 10,000 times more powerful.
Power, decibels and loudness
A person talking measures about 50 dB. It is a reasonably comfortable level of sound. You might think that ten people talking would be ten times louder. However, if you think of your experience, this is not the case. Ten people talking (in a classroom, for example) is louder than one person, but it isn’t ten times louder. This is because of the way that your ear and brain pick up sounds and interpret them.

As a rule of thumb, every ten decibel increase seems about twice as loud. However, this will vary from person to person and also depends on the pitch of a sound. So a 20 dB increase would be 100 times as powerful (10 x 10) but sound about 4 times as loud (2 x 2).

Question 1-3.

Look at the descriptions below. For each one, decide on the deciBel level that is being described. Put the number in the blank space (don't write in the unit).

Description Level
a) The level that can break bones in the ear dB
b) The level that causes pain dB
c) The level that is 1000 times more powerful than 20 dB dB
d) The level that is about 16 times louder than 10 dB. dB
Summary                   Close
  • We measure loudness using the deciBel scale
  • 10 dB rise is ten times more power
  • The quietes sound we can hear is 0 dB
  • 130 dB is painful