The guitar is a fairly simple machine. It converts kinetic energy (the movement of the strings) into sound energy. The pitch of the sound is governed by the weight of the string and where on the fretboard the player puts his fingers. The thicker strings vibrate more slowly than thinner ones and hence produce a lower note. As the player places his fingers further up the fretboard, the part of the string that vibrates becomes shorter and so the pitch increases.
Unlike an acoustic guitar, an electric guitar’s sound does not come directly from the strings. Instead, the vibrations of the strings within a magnetic field in the pickups generates a tiny electric current which can be sent to an amplifier and then to a speaker to produce the sound.
The character of the sound is affected by the body of the guitar, the type of strings & pickups, any effects that the guitarist is using like echo or distortion, the electronics within the amplifier and the design of the speaker itself.
Is that enough pretence that this is a science post? I think so.
I really just wanted to add the following two videos which show, firstly, an acoustic guitar being played by two people at the same time. Their names are Antoine Dufour and Tommy Gauthier and, apart from the brilliance of the playing, they just seem to be having lots of fun. The sound from an acoustic guitar comes from the hole in the guitar’s body which helps to project and amplify the sound made when the strings vibrate. You can just about make out that the strings the player standing up is playing are thicker (and therefore lower in pitch) than the thinner, higher pitched strings that the sitting performer is plucking.
This second video is from a Brazilian chap called Fernando Miyata who started out making these guitar videos from his bedroom at home but went on to win Guitar Idol in 2008. He is not a particularly famous rock star but he is a brilliant and inventive electric guitar player. He learned to play classical guitar first which is partly why his technique is so good. Don’t be in too much of a hurry to switch to an electric guitar! Learn your scales and your music theory first then it just takes dedicated practice to get better. He is using his feet to control some effects pedals that add the distortion (buzzing noise) to his guitar and flanging (swirling sound) he uses at the beginning. Electric guitars are generally more sensitive which is why he is able to get the strings to sound just by pressing them with the fingers of either hand. It is quite a tricky technique because you have to stop the sounds merging into one – again, it is really a matter of practice. He mostly plays with a small plastic device called a plectrum (or pick) to strike the strings but every now and again he pops it between his lips so that he can play the strings with both hands. Watch out for it, as he is very quick!
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Questions…
- What do we call a device that changes energy from one form into another?
- The frequency of a sound wave governs its pitch, but what property of a wave affects its volume?
- Apart from a guitar pickup, what other devices turn kinetic energy into electrical energy?
- What electrical component would you expect the volume control on an electric guitar to contain?
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