Violin and (Basic Physics of) Sound
The major intended audience is middle school students who attempt to understand basic principle
of physics; this article is written to enhance their understanding of relationship between violin
and sound.
Introduction
How do music instruments make sound? In order to answer this question, we need clear
definition of sound. Sound is the movement of traveling energy in form of oscillating wave.
Until this sound energy reaches human ears from a music instrument like violin, it requires
several steps: sound generation, sound transmission, and sound transduction. For this time, we
will particularly learn about different parts of a violin and how it makes sound.
Sound Generation
Major Violin Components
A violin is composed of various parts. As seen in the figure 1, the
four strings, G, D, A, E are stretched across the long neck. This
neck connects the top and body; on the top, scroll holds four pegs
which are used to tune the pitch of the four strings. The four strings
sits on the top surface of bridge and ends at the fixed end in the
middle of empty hollow body. Inside the body, a small wooden
piece called the Sound Post
is located. It is held by
friction between the top and
bottom plates. Its position
performs important role in
generating sound. Last, a
bow usually made up of
horsetail and wood.
<Figure1> Violin components
Vibration of string
There are two ways to play the violin: plucking the string by fingers —
called pizzicato—or drawing a bow across the strings. As one plays the
violin, the friction between bow hair and string causes vibration that
generates sound. Violinists increase the friction of a bow by using
supplementary tool called Rasin which is made from tree saps. Without
rasin, a bow will simply slide across the string instead of making sound
wave.
<Figure2> Sound Post
<Figure3> Rasin
Properties of Sound wave
Typically, scientists can measure and
analyze sound wave with Wavelength,
Amplitude and Frequency. As briefly
summarized in figure4, Wavelength
represents distance from a point to the
equivalent point in next phase. Amplitude
is height of the wave and Frequency is the
number of times the wavelength occurs in
a second. High frequency sound wave
produces high pitch note while low
frequency produces low pitch note. Bigger
the value of amplitude is, louder the
volume is. For this reason, sound wave
created by vibration of string itself has
relatively small amplitude, implying
volume is low. In order to successfully
transmit to human ear, we need a speaker
or an amplifier.
<Figure4> Characteristics of wave
The relationship between frequency and other factors are nicely presented in the figure below. In
the case of violin, linear mass density is constant. In addition, tension is also constant because
you tune the each strings note to GDAE by turning each peg. With the left hand, violinist plays
the note basically by press the strings to change the string length, resulting in higher frequency as
well as pitch. By bowing with right hand, they regulate the volume of the sound through friction
caused by vertical pressure as well as speed of the bow.
<Figure5> Mersenne’s Law
Sound Transmission
Amplifying the sound; the body
After the sound wave is generated, it is transmitted to different structural components of violin. It
transmits from string to bridge, bridge to sound post, and sound post to the empty hollow body.
Bridge is a wooden device that supports strings. It not only maintains same space between strings,
but also transfers wave to the amplifier. Closer a bow to the bridge, more harmonics occur. Then,
sound post receives the vibration and alters the vibration of the top plate. Combination of its
position, thickness and materials influence the tone of the sound. The empty hollow body
performs its role as a speaker, amplifying the sound it receives. As a consequence, the amplitude
of sound wave or the volume of sound increases and successfully radiates into air.
Sound Transduction
Human ear approximately has sound range from 20Hz
20,000Hz, varying depend on individual and age. As the
sound wave amplified by violin travels through ear canal and
finally reaches to Eardrum, high and low pressure of sound
wave make it vibrate. Finally, with the help of inner organs,
The sound wave successfully transfers from a violin to human
ear.
<Figure 6> Human ear
Reference
http://www.passionate-about-violins.com/violin_parts.html
http://www.violins.on.ca/luthier/soundpost.html
http://blog.kennedyviolins.com/2012/04/whats-that-shiny-lump-of-tree-sap-in-my-violincase/
http://mediainfotain.blogspot.com/2012/02/sound-wave-properties.html
http://vmsstreamer1.fnal.gov/VMS_Site_03/Lectures/Colloquium/presentations/070523Atw
ood.pdf
http://www.putnamhealingarts.com/?page_id=1475