#  Sound and Acoustics 

 



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### Velocity of Sound

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Velocity of sound is determined by measurement of the time delay of pressure pulse detected by a microphone and its distance from the loudspeaker.

### Sound Cancellation

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Feed the same signal to two speakers and reverse the connections to one of them. Result: sound cancellation!

### Double Sound Source Interference

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Young's experiment performed with coherent sound waves from two loudspeakers.

\[[In-Depth Description](/presentations/double-sound-source-interference)\]

### Refraction of Sound

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Balloons filled with helium, CO2, or SF6 act as diverging and converging lenses, respectively.

\[[In-Depth Description](/presentations/refraction-sound)\]

### Sound Reflections in Pipes

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A pulse of sound gets "inverted" when reflecting off the open end of a pipe, but does not get inverted when reflecting off the closed end.

\[[In-Depth Description](/presentations/sound-reflections-pipes)\]

### Inverse Square Intensity

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Sound pressure level of a fire bell decreases by 6dB when distance is doubled.

\[[In-Depth Description](/presentations/inverse-square-intensity)\]

### Acoustic Horn

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A multicellular horn is shown to amplify sound by 18 dB.

\[[In-Depth Description](/presentations/acoustic-horn)\]

### No Sound Through a Vacuum

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A bell, ringing in a bell jar, ceases to be heard as the bell jar is evacuated.

\[[In-Depth Description](/presentations/no-sound-through-vacuum)\]

### Doppler Ball

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Plastic Wiffle Ball with built-in shriek to throw past (or at) your audience.  
  
\[[In-Depth Description](/presentations/doppler-ball)\]

### Doppler Turntable

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Two speakers, one at each end of rotating platform; beating due to frequency shift of speakers travelling in opposite directions.  
  
\[[In-Depth Description](/presentations/doppler-turntable)\]

### Doppler Whirler

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A high-pitched alarm on the end of a rope is whirled about the head.  
  
\[[In-Depth Description](/presentations/doppler-whirler)\]

### Doppler Tuning Forks

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Run towards the blackboard carrying a tuning fork...  
  
\[[In-Depth Description](/presentations/doppler-tuning-forks)\]

### Sound Waves in a Room

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Three dimensional standing waves are generated in the lecture hall and detected by students moving about.

### Helium and Sulfur Hexafluoride

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Change pitch of organ pipes by changing sound velocity.

\[[In-Depth Description](/presentations/helium-and-sulfur-hexafluoride)\]

### Baffle

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Placing a baffle behind a tuning fork (or small louspeaker) dramatically increases the intensity of the sound.

### Contact Us

**Mailing Address**: Lecture Demonstration Services, Science Center, Rm B-08A, 1 Oxford Street, Cambridge, MA 02138  
**Campus Location**: Science Center B-08A | **Tel**: (617) 495-5824 | **Email**: scidemos-at-fas.harvard.edu