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Properties of sound waves

When an object or substance vibrates, it produces sound. These sound waves can only travel through a solid, liquid or gas. They cannot travel through empty space.

Longitudinal waves

Sound waves are longitudinal waves - the vibrations are in the same direction as the direction of travel.

The slideshow shows how you can model longitudinal waves using a long spring:

An outstretched slinky spring

Stretch the spring and hold at each end

Loudspeakers

Sound waves are produced by all vibrating objects. Loudspeakers work by converting electrical energy into kinetic energy. This moves the cone which creates the sound waves.

End of speaker cone is surrounded by a permanent magnet. A coil of wire which carries electrical signals is wrapped around the end of the cone. Movement generated causes the cone to vibrate.Cross-section of a loudspeaker showing how electrical signals travel in and out via the coil

Engineers show us the key components in a loudspeaker and explain how they work

Reflection

Sound waves can reflect off surfaces. We hear sound reflections as echoes. Hard, smooth surfaces are particularly good at reflecting sound. This is why empty rooms produce lots of echoes.

Soft, rough surfaces are good at absorbing sound. This is why rooms with carpets and curtains do not usually produce lots of echoes.

BBC Radio sound engineer Tom Parnell talks about the different microphones and speakers used for recordings at the BBC's MediaCityUK studios in Salford