Sound Extinguisher

Colin Nishitani Grant Collins

Background Problem Literature Hypothesis Materials Method Results Discussion Bibliography Link Return to Research

Sound waves are longitudinal and travel at about 343 m/s. Sound waves are made by displacing air; this is how a speaker creates sound. Flame requires three things to burn, fuel, oxygen and heat and we hope to deprive two of these things using sound waves. We believe that at a certain frequency the sound waves will displace enough air and cool the flame enough to put out the candle.

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Statement of Problem:

We want know at what frequency and amplitude a sound wave put out the flame candle.

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Review of Literature:

There must be some effects because students at University of West Georgia were able to put out fire using sound waves. They used low frequency sound waves that were at really intense levels (3). "Acoustic flow oscillations cause local changes in mixing and combustion processes in the gas phase… Subsequent variation of heat transfer to the condensed phase alters the surface pyrolysis and burning characteristics". (5) This confirms our theory that sound waves can put out a flame. "Sound appears to be a topic distinct from motion and heat. However, we now understand sound to be an ordered motion of the molecules of the medium through which the sound propagates. The study of sound provides the opportunity to understand wave motion". (7) Since one of the main components of fire is light waves then can’t sound waves affect the light waves?

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Hypothesis:

As we lower the frequency, then the amplitude for putting out the candle will decrease because of the amount of air that is being displaced will increase. Frequency and Amplitude will be set by the test tone generator

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Materials:

Computer with Test Tone Generator
Stereo with subwoofer
Constant flame source
Weights to hold everything in place
Matches and a candle

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Method:

Instead of using a candle like we stated in our Intro, we used a Bunsen burner and natural gas because the candle provided erratic data points and the Bunsen burner gave us a more consistent flame that provided more steady data. We used a computer with a Test Tone Generator to provide a given frequency and accurate way to monitor amplitude. We connected a home stereo system with a subwoofer to our computer to provide us with a sound source. We kept the volume on the stereo and the computer at a constant, so that we would get accurate results throughout the experiment.

Our original plan was to put the flame source in front of the speaker on the sub, but that didn’t displace enough air to put out the flame, so we placed the flame in front of the port; which displaced more air than the front of the speaker. The Bunsen burner was 6 centimeters away from the port. We adjusted the flame to an appropriate level using the gas, so that it wasn’t too intense to put out. We used weights and tape to prevent the sub and the Bunsen burner from moving around due to the vibrations. We kept a lit candle with us so we could easily relight the flame when it went out. We did three trials for each data point to ensure that the data was correct, since we had troubles earlier with the candle. We hypothesized that it would work better with lower frequencies, so we started with 50 Hertz and we set the lowest amplitude possible that would put the Bunsen burner flame out, which was -6 dBFS. We continued decreasing the Hertz by 2 each time, and we choose the lowest amplitude that would put out the flame. We continued this pattern until we reached 32 Hz, then we did several tests above 50 Hz to make sure our patterns and data was accurate. The Test Tone Generator was used because it was a good way to insure that the frequency and amplitude were accurately monitored.

Data File

As you can see from our graph for the most part the data showed that the lower the frequency, the less amplitude was required to put out the flame. There was a spike in the amplitude from 34 to 32Hz. The first source of uncertainty is the fact that we were using Test Tone Generator, an older computer and an older stereo and even though we tried to keep everything constant the amplitude and frequency could have fluctuated slightly as we were gathering data. Another source of uncertainty is the fact that we weren’t consistent in how long we let the flame go for before produced the tone. Also sometimes the tone took longer than other times to extinguish the flame. The further into the experiment we got the more unburned hydrocarbons could have been oxidized to the Bunsen burner causing it to burn more or less intensely.

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Discussion:

Our data supported our hypothesis because it showed a direct relation between frequency and amplitude. As we decreased the frequency the lowest possible amplitude for putting out the candle also went down. Our sound wave was sinusoidal, we know this because it was set by Test Tone Generator, and frequency is the distance between the peaks of each wave. A speaker makes sound by displacing air the lower the frequency the faster it moves in and out. And if the speaker is moving faster it will displace more air, moving faster, thus being able to put out the flame with less intensity. A good example of why this works is when you put your hand in front of a big subwoofer you feel the sound waves against your hand, whereas no matter how loud you make a tweeter all it can do is hurt your ears. Around 36 Hz the amplitude for putting out the flame started to go back up and we have several theories to explain this. The first is that the displacement of the speaker enclosure and the diameter of the port and the number of baffles all create an environment in which only resonates well at certain frequencies. The second would be that eventually the speaker would reach its terminal velocity and just couldn’t move any faster or generate any lower frequencies. In order to perfect this experiment we would use more expensive sub that would be capable of generating any frequency desired. It would also be better if had a flame source that would stay exactly the same no matter how long it had been burning or how many times it had been relit.

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Bibliography:

1. Helminstine, Marie. "Q. What is the State of Matter of Fire or Flame? is It a Liquid, Solid, or Gas?" About.Com. 2007. 29 Oct. 2007 < http://chemistry.about.com/od/chemistryfaqs/f/firechemistry.htm >

2. Henderson, Tom. "Standing Wave Patterns." Gleenbrook. 2007. 29 Oct. 2007 </gbssci/phys/Class/sound/u11l4c.html>.

3. O'Meara, Stephen James. "The power of sound." Odyssey 15.3 (March 2006): 6(4). General Reference Center Gold. Gale. Tualatin High School. 29 Oct. 2007
<http://find.galegroup.com/ips/start.do?prodId=IPS>.

4. Port, Otis, and Catherine Arnst. "Noise Alone May Quench the Flames." Business Week 3 Oct. 2005: 1. Ebsco. Tualatin High. 29 Oct. 2007. Keyword: Sound Waves and Fire.

5. Roh, Tae-Seong. "Effects of Acoustic Oscillations on Flame Dynamics of Homogenous Propellants in Rocket Motors". American Institute of Aeronautics and Astronautics, Inc. 1995.

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Sound Waves Snuff Fire. A brief insight to the quandary of putting a flame out using sound

Fighting Fire with Sound. NASA wants to utilize new technology to use sound waves to extinguish flames in zero gravity.

Research about Sound Waves. Another experiment that paralleled ours, and contains a very detailed account of their procedure.

Myth Busters! They attempted to replicate a similar experiment, only they were aiming to extinguish the flame with a human voice