SOUND WAVES IN INSTRUMENTS

BY SAMANTHA YANG

LET’S START WITH THE BASICS…

• A wave is the motion of a disturbance, sometimes with a medium, sometimes without

• A mechanical wave travels through a medium, or physical material

• Sound waves are a form of mechanical wave that may travel through mediums such as water or air

• Sound waves are a longitudinal wave, which means the direction of the particles of the medium is parallel to the energy transport

• A sound wave is introduced by a vibrating object such as a violin string or a tuning fork

A WAVE TRAVELING THROUGH A MEDIUM

PITCH AND FREQUENCY

• Frequency is measured in Hertz which may be defined as vibration(s)/second

• Pitch is how high or low the sound is perceived

• Humans can hear from a range of 20Hz to 20,000Hz

• The higher the frequency, the higher the pitch

• Lower frequencies tend to be louder

AN EXAMPLE

For any guitar players out there, here is a table of the frequency of each string- note the trend of lower notes decreasing in frequency

CHECK FOR UNDERSTANDING

John built a frequency counter that measures frequency. Testing it out, he found that the highest note of his favorite song is 24,000Hz. Is this reasonable? Explain why or why not.

• No it is not because humans can only hear from 20 to 20,000 Hz of frequencies

What causes a mechanical wave?

• A disturbance or vibration

Is it possible for a wave to travel without a medium? List an example

• Yes, electromagnetic waves may travel in a vacuum or through space

INTENSITY

• The amount of energy that is transported past a given area of the medium per unit of time is known as the intensity of the sound wave

• Units of intensity are Watts/meter2

• Intensity may also be measured in decibels

• As a sound wave carries its energy through a two-dimensional or three-dimensional medium, the intensity of the sound wave decreases with increasing distance from the source.

INTENSITY OF INSTRUMENTS

• Piano – 60 to 70 decibels

• Cello – 82 to 93 decibels

• Violin – 80 to 103 decibels

• Flute – 93 to 111 decibels

• Trombone – 85 to 114 decibels

SOME USEFUL FORMULAS…

• Speed = Wavelength/ Period = Wavelength(Frequency) => v = f • λ

• Linear mass density = Total Mass of string / Length of string => μ = M/L

• Intensity = Power/Area => I = P/A

CITATIONS

• Linden, Joshua. "Pitch and Frequency." Pitch and Frequency. The Physics Classroom, 3 Dec. 2013. Web. 11 Feb. 2015.

• Marshall, Chase. "H.E.A.R. Are You At Risk?" H.E.A.R. | Are You At Risk? | Hearing Education and Awareness for Rockers. H.E.A.R Net, 14 Jan. 1998. Web. 18 Feb. 2015.

• Wolfe, Joe. "Strings, Standing Waves and Harmonics." Strings, Standing Waves and Harmonics. University of New South Wales, 11 Oct. 2011. Web. 13 Feb. 2015.