A Practical Application of Destructive Interference

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A Practical Application of Destructive
Interference
Electronically identifies and reduces unwanted
sound while faithfully preserving the audio or
tranquility you desire. --Bose Audio
Created byJake Druck
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The Problem
When listening to music with traditional
style headphones, there is often too much outside
(ambient) noise interfering with the music that
you are trying to listen to. When trying to
listen to your mp3 player, your ears are
overwhelmed by background noise from outside
sources. The obvious solution for this problem is
to turn the volume up until your ears begin to
bleed. Unfortunately that isnt too great for
your ear drums and will undoubtedly lead to a
life of asking others to repeat themselves.
The Solution
In 1978, a gentleman named Amar Bose was on
a flight to Europe when he was annoyed by the
overwhelming noise of the jets engine that
prevented him hearing his music. He came up with
the idea of using the headphones themselves to
reduce unwanted ambient noise. A decade later
came the production of the first pair of noise
canceling headphones. They operate in the same
way that traditional headphones do, converting
electrical waves into longitudinal sound waves
that the human ear can interpret. The difference
in the noise canceling headphones is their
implementation of both active and passive noise
reduction systems. I will explain these systems
in further detail throughout the PowerPoint.
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The Physics Behind It All
In class, we discussed the properties of
sound waves and the interference that occurs when
two waves come in contact with one another. The
Superposition Principle states that the
amplitudes of two or more waves are added to one
another at the point where they overlap.
Destructive interference occurs when the
superposition of the waves is smaller than the
individual waves. Maximum or complete destructive
interference occurs when crest of one wave meets
the trough of another wave. When this occurs, the
waves are said to be exactly out of phase.
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Active vs. Passive Noise Control
Most traditional headphones provide some
sort of passive noise control. The material that
the headphones are composed of block out some of
the higher frequencies. An example of a material
that is a good sound insulator is high density
foam, which helps keep ambient sound out. The
best passive headphones used today can help
reduce outside noise by 15-20 decibels.
Active noise canceling is more of a technical
process than a physical barrier. It helps reduce
low frequency sound waves by recording the
ambient noise and then duplicating a sound wave
that is out of phase resulting in destructive
interference. It helps to account for an
additional reduction of around 20 decibels.
Protective earmuffs and high density foams
provide excellent passive noise control
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The Components
Microphone-Records ambient noise Electronic
Circuitry-Produces the out of phase sound wave
that replicates ambient noise Speaker
-Responsible for taking electrical signals and
converting them into sound waves Casing-Helps
enclose electrical components and aids in
passive sound control Battery-provides
additional power for active sound control
Taken from howstuffworks.com
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Disadvantages
Although there are many obvious advantages
to using noise canceling headphones, I felt
compelled to list several disadvantages.
-Requires the use of a battery -Bulky, heavier
design -Occasional high frequency hiss due to
stray electromagnetic fields -Works best only
when ambient noise is steady and at a low
frequency -The microphone picks up on wind and
can render the headphones useless
The Advancement of Acoustic Technology
After researching how destructive
interference was applied in noise canceling
headphones, I realized that there is a whole
world of acoustic products that rely on the
superposition principle. Through the advancement
of new technologies in this field, Im confident
that we will continue to see, or rather hear,
better quality sound and music in the years to
come. Its crazy to think that maybe someday we
will hear music that is 100 free of ambient
noise. Constructive interference, an idea that I
failed to mention in the PowerPoint, also has
many uses. Microphones and loudspeakers operate
using this technology. This project has provided
me with a better insight into the practical
applications of wave technology. I look forward
to seeing what further advancements the future
has to bring!
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Works Cited
http//www.bose.com/controller?eventVIEW_PRODUCT_
PAGE_EVENTproductqc3_headphones_featurestabs ht
tp//electronics.howstuffworks.com/noise-canceling
-headphone.htm https//physclass.physics.phys.psu.
edu/lectures/p001/lecture10A.ppt