Sound and noise

Sound

Sounds are carried by longitudinal waves where the particles of the medium vibrate in the same direction as the energy of the sound is carried.

Humans can hear sounds in the range 20 hertz to 20,000 hertz. This is often referred to as the range of hearing. Not everyone can hear over all of this range - the numbers are only approximate. In particular the high frequency limit reduces with age.

The loudness of a sound is a measure of the amplitude of the wave. The greater the amplitude, the louder the sound.

The pitch of a sound is a measure of the frequency of the wave. The higher the frequency, the higher the pitch.

Frequency and pitch

Frequency and amplitude

Noise

We are virtually always subjected to sounds. Unwanted background sounds are sometimes called noise. When the sound level of this noise rises to higher levels, we refer to this as noise pollution.

Sound levels and noise

Sound levels are measured on a scale known as the decibel dB scale. The higher the number the greater is the sound level.

Too much noise can damage hearing. Exposure to 90 decibel sound levels for a long time can cause permanent hearing loss. Exposure to a brief sound level of 140 decibels will cause pain and can cause permanent damage to hearing.

Example sound levels for different sounds are: whispering -20 dB, background noise at home -40 dB, normal speech -60 dB.

Try this:

Question

The table gives the sound levels of some sources of sound. Enter the following sources of sound in the correct places.

  • Background noise at home
  • At a concert - 1 metre from a loudspeaker
  • Normal talking
  • Whispering
Sound levels of sources of sound
Source of SoundSound level in decibels
Threshold of sound0
20
40
60
Noise pollution level90
Pneumatic drill - 5 metres away100
120
Threshold of pain140
Sound levels of sources of sound
Source of SoundSound level in decibels
Threshold of sound0
Whispering20
Background noise at home40
Normal talking60
Noise pollution level90
Pneumatic drill - 5 metres away100
At a concert - 1 m from a loudspeaker120
Threshold of pain140