Guitars are the most popular and common instrument of the string family. The guitar has been around for thousands of years and is still prominent in modern music. While a guitar is not the most complicated instrument there still is a lot of physics behind the process of making sound from a string. To fully understand how a guitar works we first need to understand what exactly sound is, so that’s where we’ll start. GUITARS
Sound is energy in the form of waves caused by vibration Formed when air particles vibrate from the vibrating object around them and travel in wave shapes called longitudinal waves. The waves are made up of areas of high pressure called “compressions” and areas of low pressure called “rarefactions” WHAT IS SOUND?
WAVE LENGTH The wave length of a sound wave is one complete cycle of the wave at two equal successive points. (one compression and rarefaction) AMPLITUDE The amplitude is the height of the wave. The higher the amplitude the louder the wave. PARTS OF A SOUND WAVE
FREQUENCY The frequency of a sound wave is the number of cycles that pass a certain point in a second. Frequency is measured in Hertz. Another way of talking about frequency is pitch. They are basically the same thing. The higher a sound’s pitch is the higher the frequency of the wave. Pitch is usually associated with music. VIDEO OF DIFFERENT FREQUENCIES http://www.youtube.com/watch?v=igGroIcga3g&feature=related PARTS OF A SOUND WAVE
PARTS OF A GUITAR
The most important part to a guitar sound is the strings Modern guitar strings are usually made from either nylon or steel, nickel, and bronze. They are stretched from the bridge of the guitar over the body and fret board, against the nut and into the tuners (which adjusts the tension of the strings to the desired notes). When the guitar player plucks the strings it causes them to vibrate which causes the air around the string to vibrate thus making a sound wave. The frequency that a string produces is determined by the mass, length, and tension of the string. Heavier strings vibrate more slowly Higher tension raises the pitch Shorting the string raises the pitch STRINGS
Strings are fixed at each end which is why they are able to vibrate. The parts of the string that are unable to vibrate are called the nodes. The parts where vibration is present are called antinodes. When the string is plucked the note we hear is called the fundamental frequency or the 1st harmonic. There are also many other frequencies that are produced when the string is plucked. These other frequencies are called “Harmonics” or “Overtones”. STRINGS
When a string is plucked it vibrates in more than one way. The string vibrates in many different shapes and directions which produce many different amplitudes and frequency waves which are called harmonics. The string can vibrate as if it was two half strings with a node in the middle or as three third-strings and so on. The harmonics are not regular sound waves they are called standing waves because they do not travel. Harmonics are what causes a guitar to sound the way it does and not just boring simple sounds. Good Animation: http://id.mind.net/~zona/mstm/physics/waves/standingWaves/standingWaves1/StandingWaves1.html HARMONICS
ACOUSTIC GUITAR BODY
If it wasn’t for the body of aguitar the vibration of the strings would barely be audible. The body of the guitar amplifies the sound of the strings so the sound can be heard. When the player plucks the guitars strings, the strings vibrate, which transfers the mechanical energy down the strings to the guitars bridge which is attached to the guitars body. When the energy is transferred to the bridge it cause the top plate (also called the soundboard) of the body to vibrate as well. The sound board is usually made form a thin piece of wood with bracing on the underside to support the soundboard but this bracing also has a significant impact on the sound the guitar makes. GUITAR BODY BRIDGE
When the soundboard of the guitar vibrates it causes the air inside the body of the guitar to vibrate as well.
When the molecules of air closest to the soundboard start vibrating they bump into the other particles around them and they start to vibrate and so on.
The air particles inside the body are vibrating at a common frequency which is the sound that is produced.
All the air inside the body of the guitar is vibrating and this sound and vibrating air has to go somewhere.
The sound hole is where all the vibrating air and sound escapes from the guitar’s body. Which is how the sound of the instrument is projected to the listeners. SOUNDHOLE
ELECTRIC GUITAR BODIES & ELECTRONICS
The only real differences between electric guitars and acoustic guitars is that electric guitars have a solid wood body and they have electronic pickups to amplify the sound. They also have all the electronic wiring and controls need to work the guitar. ELECTRIC GUITAR
The pickups of the guitar pick up the sound vibrations from the plucked string and convert them into electronic signals which are read by the amplifier. The pickups are essentially electromagnets and consist of a bar magnet wrapped in fine wire. The electromagnet turns the vibration energy into electrical energy by the vibrating steel strings causing a corresponding vibration in the magnet’s magnetic field, which turns into a vibrating current in the coil. PICKUPS
EXAMPLES OF GUITAR SOUNDS ACOUSTIC ELECTRIC http://www.youtube.com/watch?v=6VAkOhXIsI0 Starts at :30 seconds. http://www.youtube.com/watch?v=NUHhUy6sBiQ
Brain, Marshall. "How Acoustic Guitars Work." HowStuffWorks. How Stuff Works, Inc, Web. 6 Dec 2009. http://entertainment.howstuffworks.com/guitar1.htm. Brain, Marshall. "How Electric Guitars Work." HowStuffWorks. How Stuff Works, Inc, Web. 6 Dec 2009. http://entertainment.howstuffworks.com/electric-guitar1.htm. Cross, Dan. "The Soundboard: A Primer." About.com. The New York Times Company, Web. 5 Dec 2009. <http://guitar.about.com/od/helpbuyingguitarsgear/a/gtr_soundboard.htm>. Johnson, Greg. "How does a Guitar Work?." ehow.com. Demand Media, Web. 3 Dec 2009. <http://www.ehow.com/how-does_4579020_a-guitar-work.html>. "Physics Tutorial: Guitar String Harmonics." Physics 24/7. Web. 2 Dec 2009. <http://www.physics247.com/physics-tutorial/guitar-string-harmonics.shtml>. "Sound is a Pressure Wave." The Physics Classroom. The Physics Classroom, Web. 20 Nov 2009. http://www.physicsclassroom.com/Class/sound/u11l1c.cfm "The Physics of Sound." The Method Behind the Music. Number A Productions, Web. 21 Nov 2009. <http://method-behind-the-music.com/mechanics/physics>. "The Physics of Sound." The Soundry. Web. 1 Dec 2009. <http://library.thinkquest.org/19537/Physics2.html>. Wolfe, Joe. "How does a guitar work?." The University of New South Wales. Web. 2 Dec 2009. <http://www.phys.unsw.edu.au/~jw/guitar/intro_engl.html> Wolfe, Joe. "Strings, standing waves and harmonics." The University New South Wales. Web. 2 Dec 2009. <http://www.phys.unsw.edu.au/jw/strings.html>. WORKS CITED