Topic: Sound waves

 Short discussion Every time we speak or make a noise we create sound waves. What are echoes? What other kinds of waves are there? Think of a stone dropping into a pond of water...

 Listen to the sound of the note A above middle C on a tuning fork, violin and flute and also to the sound of crashing cymbals. If you do not have these instruments in class, click on the icon to open a MIDI version. Look at the notation file to see the note A on the stave. Now have a look at the sound waves below. The note A produces the first three waveforms (on tuning fork, violin and flute) and the final waveform illustrates a 'note' played by cymbals.

 Courtesy Dorling Kindersley Encyclopedia UK

 Read this description of the waveforms. Test your understanding by completing this Cloze exercise.

 Each sound has its own unique harmonic structure that distinguishes it from all other sound. The word 'harmonic' will be dealt with in lesson 4.

 Discussion What causes sound waves and how are these translated by the ear? Read this step-by-step account. Discuss it. Then try, in pairs, to say by heart all the stages from 1 to 9.

 When an instrument is played, part of it vibrates.  This produces sound waves in the air.   The waves are small but they cause rapid changes in air pressure at the same rate as the vibration of the instrument.   The sound wave from each instrument has its own kind of pressure changes.  These can be shown by waveforms - as above.   Therefore each waveform is created by a particular pattern of vibration in an instrument.   Music causes our eardrums to vibrate in the same pattern as the instruments being  played.   These vibrations are interpreted by the brain so that we can recognise which instrument  is being played.   It's called timbre or sound quality.

 Notice that the peaks in all the waveforms above occur at the same places - except in the case of the cymbals. The note A above middle C always produces 440 peaks a second, no matter what instrument plays it.  It has a frequency of 440Hz. An object vibrating to produce sound is actually vibrating at several frequencies at once.  The blending of these "pitches" gives a sound its timbre.  The better these "pitches" blend, the better the sound quality.

 When a listener can judge that two sounds are dissimilar regardless of similar pitch, loudness and duration - that's timbre.

 Websearch Give the above information in diagram form, with a drawing of the sound source on one side of the page and a drawing of the ear on the other. What happens in between? For more information on the ear and its interpretation of sound.

 Student home Project home