Maton Guitars - Stand alone

PROJECT 1 – THE SCIENCE OF SOUND AND GUITAR STRINGS

SOUND

• Sounds are vibrations of the air caused by a vibrating source
• “Any sound, whatever it may be, is caused by something vibrating. In other words, by something which is moving back and forth, either in a regular manner or in a random manner, about the position it occupies when at rest. The source of the sound may be a car engine, a burglar alarm or a bird singing. Whatever it is, some part of it must be vibrating for it to produce sound”. [Quote source]

 

TRY: Feel the sound

• Hum with a finger on your throat to feel your voice box vibrating

VIBRATION

• Vibration is an oscillation (back and forth movement) of air pressure caused by vibrating objects

ENERGY

• If you exert force on a string – potential energy is transferred into kinetic energy as the string moves back and forth until it comes to rest in potential energy again

WATCH: Simple Harmonic Motion

TRY: See and feel vibration

• Pluck a guitar – see how strings move back and forth
• Hit a drum with beads sitting on its surface – watch the energy of tone causing the beads to move
• Hit a drum and touch its skin – feel the vibration through your hand
• Hit a tuning fork on a table and then place near a container of water – watch how the vibration of the fork moves the water
• Cup and string activity – notice how the sound travels down the string to your ear [Lesson Plan]
• Play a kazoo – notice how your voice causes the membrane to vibrate and make a buzz

WATCH: Sound Crash Course

HEARING

• “When we hear a sound, what our ears are actually doing is converting the rapid fluctuations in air pressure that make up a sound wave into neural impulses. The human ear comprises three fairly distinct sections; the outer ear, the middle ear and the inner ear”. [Quote source]

• Sound is also felt in the body

WATCH: Touch the Sound

Touch the Sound is a documentary about Dame Evelyn Elizabeth Ann Glennie, a Scottish virtuoso percussionist. She has been profoundly deaf since the age of 12 and taught herself to hear with parts of her body other than her ears

SOUND TRAVEL

• Sound needs a medium to travel through from the source of the sound to the ear in the form of a gas, solid or liquid
• Sound travels faster in water than in air (the particles in liquid are closer together and so allow a quicker transference of their energy)
• “The vibrations of a sound source cause the neighbouring air molecules to be alternately squeezed together and pulled apart. These air molecules then push and pull against their neighbours which, in turn, push and pull against their neighbours. In this way, a series of compressions (regions of higher pressure) and rarefactions (regions of lower pressure) is generated which travels away from the vibrating source. This sequence of pressure fluctuations is what we refer to as a sound wave”. [Quote source]

TRY: Air pressure with a slinky or rope

• In pairs, each hold one end of an outstretched slinky
• One person holds the end steady, the other person pushes the slinky towards their partner (this will be easier if the slinky is resting on a surface such as a desk or the floor)
• This movement will cause a compression and rarefaction of the slinky as the energy is transferred along the slinky until it reaches the other person
• This is a visual demonstration of how air particles are moved when excited by energy such as vibration (this can be explained as the sound being made at one end – with vibrations that disrupt air particles until the sounds reaches the ear at the other end)

WATCH: Sound wave motion animation

• Look at how this slinky soundwave example looks at a molecular level. This is also what a sound wave looks like (formed by high and low air pressure moving through time)

WATCH: Vibrating guitar strings

• Look at how each string is vibrating – the shape the string is making is also its corresponding waveform

SPEED OF SOUND

• The speed of sound is a constant and allows us to measure how many waves are occurring as they reach our ears
• The speed of sound depends on the state of the gas – on Earth the atmosphere is composed of mostly nitrogen and oxygen and the temperature depends on the altitude
• At sea level at 21 degrees and normal atmosphere the speed of sound is 344 meters per second

PITCH/FREQUENCY

• Guitar example: because the speed of sound is constant – if you could count how many sound waves reach you per second – you would know how many times the string vibrates (moves back and forth) in a second – this number is called the sounds pitch or frequency – the rate at which the waves pass a given point and the rate at which a guitar string or a loudspeaker vibrates

WATCH: Sound Waves

TRY: Ruler and pitch activity

• Hold a ruler flat on a table with some length of the ruler hanging over the edge
• Hit the end that is hanging over the edge and notice the pitch it makes
• Pull more or less of the ruler over the edge and hit this end again
• Notice how the length of the vibrating section of the ruler effects the pitch of the sound
• The more the vibrating ruler is over the edge of the desk, the lower the pitch

WAVELENGTH

• A wavelength is the distance between two troughs or peaks of a wave
• Wavelengths are measured in Hertz

TRY: Chrome Music lab sound waves activity

• Click a note on the keyboard to hear the note and see how the air particles are displaced
• Click on the magnifying glass to see the sounds corresponding wavelength
• Try playing low and high notes and notice the difference in the wavelength

TRY: Online vibration activity

• Look at the vibration speed and intensity of a sound
• The vibration speed is the frequency and the vibration intensity is the amplitude
• Notice – the more air is moved, the larger the waveform and the louder the sound
• Notice – the faster the air is moved, the closer together the waveform and the higher the sound

TRY: Frequency and amplitude with a slinky or rope

• In pairs, each hold one end of an outstretched slinky or rope – rest the slinky on a surface such as a desk or floor
• One person hold the end steady, the other person oscillate the rope up and down slowly and then quickly – this will demonstrate the frequency or rate of oscillation of the rope
• Try again but this time one person keeps the frequency the same but changes the amount of energy passes through the rope – this will demonstrate the changing amplitude of the rope

NATURAL FREQUENCY

• “The frequency or frequencies at which an object tends to vibrate with when hit, struck, plucked, strummed or somehow disturbed is known as the natural frequency of the object”. [Quote source]

TRY: Frequency of strings

• Make a string experiment with a box, rubber bands and bridge (you can use pencils for the bridge)
• Move the bridge to demonstrate how the length of a string determines the frequency of the sound produced
• String Experiment
• Build a guitar

TRY: Chrome Music Lab – Strings

• “This experiment lets you explore the natural mathematical relationship between a strings length and its pitch. For example, the second string is half the length of the first, and it plays the same note an octave higher.”

GUITAR STRING FREQUENCY

• Factors effecting the frequency of guitar strings are length, tension, density and thickness
• “A guitar has six strings, each having a different linear density (the wider strings are more dense on a per meter basis), a different tension (which is controllable by the guitarist), and a different length (also controllable by the guitarist). The speed at which waves move through the strings is dependent upon the properties of the medium - in this case the tightness (tension) of the string and the linear density of the strings. Changes in these properties would affect the natural frequency of the particular string. The vibrating portion of a particular string can be shortened by pressing the string against one of the frets on the neck of the guitar. This modification in the length of the string would affect the wavelength of the wave and in turn the natural frequency at which a particular string vibrates at. Controlling the speed and the wavelength in this manner allows a guitarist to control the natural frequencies of the vibrating object (a string) and thus produce the intended musical sounds”. [Quote source]

TRY: String Experiment

• Use the string experiment with a box, rubber bands and bridge again
• This time use rubber bands with different thicknesses to demonstrate how the strings thickness effects the frequency produced
• Also try tightening the rubber band to demonstrate that the tension of the string also effects the frequency produced

EXTENSION FOR LOWER SECONDARY
STANDING WAVES

• “A standing wave is the pattern produced in a medium as the result of the repeated interference of two identical waves moving in opposite directions through the medium. All standing wave patterns have nodes and antinodes. The nodes are points of no displacement caused by the destructive interference of the two waves. The antinodes result from the constructive interference of the two waves and thus undergo maximum displacement from the rest position.
• Antinodes: The points in a standing wave with maximum displacement from the resting position. The antinodes result from the constructive interference of the two waves. This means the waves are in phase and the combination of their energy moves the medium the greatest distance from its resting position. Nodes: The points in a standing wave with no displacement.
• Nodes result from the destructive interference of the two waves. This means the waves are out of phase (one wave moves up and the other wave moves down) and the combination of their energy is zero. Thus the medium doesn’t move at all”. [Quote source]
• “The pattern above is not the only pattern of vibration for a guitar string. There are a variety of patterns by which the guitar string could naturally vibrate. Each pattern is associated with one of the natural frequencies of the guitar strings. Each standing wave pattern is referred to as a harmonic of the instrument”. [Quote source]

TRY: Chrome Music Lab - Harmonics

• “The harmonic series is a set of frequencies with a simple relationship: twice as fast, three times as fast, four times, and so on. Musical intervals emerge from this natural phenomenon, such as the octave and the major chord”

TRY: Standing waves with a slinky

• In pairs, each person hold one end of an outstretched slinky or rope
• One person hold the end steady, the other person oscillates the rope up and down slowly to produce the fundamental 1st harmonic
• Try this again now increasing the vibration to produce the 2nd harmonic and continue to attempt to produce 3rd and 4th harmonics

WATCH: Online demonstration of slinky activity

WATCH: The physics of playing guitar

TRY: Open-string and fretted harmonics lesson

RESONANCE

• “If you were to take a guitar string and stretch it to a given length and a given tightness and have a friend pluck it, you would hear a noise; but the noise would not even be close in comparison to the loudness produced by an acoustic guitar. On the other hand, if the string is attached to the sound box of the guitar, the vibrating string is capable of forcing the sound box into vibrating at that same natural frequency. The sound box in turn forces air particles inside the box into vibrational motion at the same natural frequency as the string. The entire system (string, guitar, and enclosed air) begins vibrating and forces surrounding air particles into vibrational motion. The tendency of one object to force another adjoining or interconnected object into vibrational motion is referred to as a forced vibration. In the case of the guitar string mounted to the sound box, the fact that the surface area of the sound box is greater than the surface area of the string means that more surrounding air particles will be forced into vibration. This causes an increase in the amplitude and thus loudness of the sound”. [Quote source]
• “This is an example of resonance - when one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion.” [Quote source]

TRY: Resonance activity

• Place rubber bands over containers of varying sizes to demonstrate how different sized resonating chambers amplify more or less and what area of the frequency spectrum they amplify more or less
• This can be done with a tuning fork as well – hit the tuning fork with a rubber mallet and notice the amplitude of the fork. Try this again but rest the tuning fork on a desk or window or whiteboard – the amplitude will be greater as the tuning fork forces the surrounding surface particles into vibrational motion. The surface will force the surrounding air particles into vibration and so the amplitude of the sound will be increased

Further reading on guitar acoustics