6'163 Final Project

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6.163 Final Project
The Study of Sound Waves through Planar Objects
Cheng-Wei Pei Joe Stark Will Tetteh Debbie Wan
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Contents

• Overview of Project
• Sound wave theory
• Experimental results
• Conclusions
• QA

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Overview of Project
GOAL Measure the effects of a planar medium on
sound waves and determine the frequency response
of the planar medium.
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Experimental measurements

• We visualized sound waves using Schlieren
  photography, a ripple tank, and stroboscopy.
• We found that sound waves are very difficult to
  visualize using Schlieren.

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Experimental measurements

• The inputs to the system can be either impulses
  or fixed frequencies.

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Contents

• Overview of Project
• Introduction to sound wave theory
• Experimental results
• Conclusions
• QA

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Introduction to Sound Wave Theory

• Sound waves travel through air via periodically
  varying pressure and temperature gradients.

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Sound Wave Theory

• Sound waves travel through solids via mechanical
  vibrations of the solid.
• In fluids, sound waves can be seen on the fluid
  boundary layer as vibrational waves

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Contents

• Overview of Project
• Introduction to sound wave theory
• Description of Schlieren photography
• Experimental results
• Conclusions
• QA

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Experimental results Part I

• The speaker and amplifier
• Goal is to stimulate medium with acoustic energy
  generating waves
• Speaker delivered 255 watts of power from
  amplifier to medium.

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Part I The speaker amp

• Visualization is key
• Using Schlieren wine glass, pane of glass, air
  cavity
• Using Stroboscopy and Flash ripple tank and
  wine glass

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Part I The speaker amp

• Results
• with the wine glass, we can see the glass change
  shape as it vibrates at the resonant frequency
  (using the Strobotac)
• energy transfer is more efficient between solids

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Part I The speaker amp

• speaker alone, we can see air movement with
  Schlieren

• Schlieren did not yield visible results for
  actual sound waves, but can see glass distortion

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Experimental results Part II

• High Voltage Discharge
• 400 Volts are discharged across a small gap (2
  mm), creating a spark
• Discharged both under water and in air

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Part II High voltage discharge
Test medium water and air Visualization method
Strobotac, Microflash, and Schlieren
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Part II High voltage discharge

• Results
• can visualize heat conduction through water

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Experimental results Part II

• The Exploding Wire
• 400 volts dropped across a very fine piece of
  wire, causing it to vaporize

• creates bright flash of light and loud pop

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Part II The exploding wire
Test medium -- wine glass Visualization method --
Schlieren
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Part II The exploding wire
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Part II The exploding wire

• Results
• calculated speed of sparks coming off exploding
  wire0.7m/sec.
• measured amount of light emitted by exploding
  wire26 BCPS.

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Experimental results Part III

• Ripple Tank
• wine glass placed in small tank filled with water

• wine glass resonated with finger

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Part III Ripple Tank

• observed effect of resonating wine glass in
  water
• used flash photography and digital camera to
  capture images of standing waves

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Part III Ripple Tank

• Results
• can visualize sound waves (as mechanical
  vibrational energy) in water
• sound output was approximately 72 dB, but need
  122 dB to visualize with Schlieren

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Part III Ripple Tank

• Results
• can visualize sound waves on fluid boundary
  using Flash photography

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Part III Ripple Tank
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Contents

• Overview of Project
• Introduction to sound wave theory
• Description of Schlieren photography
• Experimental results
• Conclusions
• QA

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Conclusions

• subsonic waves are difficult to visualize in air
• changes in light diffraction that can be
  visualized with Schlieren are limited

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Conclusions

• geometry of wine glass causes it to resonate
  with 4 nodes
• air is a poor medium for visualizing sound or
  mechanical energy produced by vibrations

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Conclusions
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Contents

• Overview of Project
• Introduction to sound wave theory
• Description of Schlieren photography
• Experimental Results
• Conclusions
• QA

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Questions?