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4. Sound: health and safety issues, hearing frequency ranges of animals, use of microphone and loudspeaker

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4a. Sound and health and safety

 

The graph shows the safe time limits for levels of sound measured in decibels (Db).

If your work involves noisy machinery, you should wear good quality ear defenders.

Industrial ear muffs have built in layers of soft material to absorb high amplitude (loud) sound waves.

We can tolerate loud sounds for a short period, though ear drum damage can still occur.

Apparently the biggest danger of loss of hearing in later life comes from many hours of repetitive fairly loud sound, which at the time doesn't seem harmful - beware of discotheque experience!!!

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4b. The frequency limits of hearing of some animals

TYPICAL FREQUENCY HEARING RANGES (Hertz, Hz)

Many animals can hear much higher frequency sounds than us humans.

Bats use high frequency echo location waves to sense the world around them.

Dolphins (and whales) use high frequency sound for communication.

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4c. The microphone and loudspeaker

The diagram above illustrate the principle of a microphone e.g. for a vocalist or a telephone mouthpiece.

A microphone converts the energy of the pressure variation of sound waves into an electrical energy signal in an ac current.

The oscillation of the sound waves vibrates the diaphragm which generates an oscillating signal in the electrical circuit.

In some ways the effect is similar to how your ear works!

The electrical signal could in turn be used to re-generate sound in a loudspeaker.

In loudspeakers, an ac current conducting coil is moved by in a magnetic field to convert electrical energy into sound energy by way of a vibrating cone (diaphragm).

The cone vibrates the air and the oscillations produce the sound waves you hear.

For more details see the electricity and magnetism notes:

11.6 The loudspeaker - an application of the motor effect

12.5 How does a microphone work?

INDEX of physics notes on SOUND

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Keywords, phrases and learning objectives for sound waves

Be able to discuss health safety issues of sound levels (loudness) and be able to describe and explain precautions like ear defenders.

Know the decibel is the unit of the loudness scale (amplitude levels).

Appreciate the there are different hearing frequency ranges of different animals/

Know the use of microphone and loudspeaker to record or enhance sound levels.

See electricity and magnetism section

Part 11.6 The loudspeaker - an application of the motor effect

Part 12.5 How does a microphone work?

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