1. The Effect of Density on Sound Propagation Matthew Van Beek Aberdeen Central High School Purpose Hypothesis Methods Graphical Representation of Data 1. Place the source of the sound (laptop speakers) 35 cm away from the Decibel Reader. 2. Turn the volume to maximum on the tone generating software and the laptop. 3. Play the sound at 100 Hz, then record the data. 4. Repeat step 3 for 1,000 Hz and 10,000 Hz. 5. Place the object (Wood, Plywood, Foam, Cement, or Rubber) between the speakers and the Decibel Reader, so that the object is 1 cm away from the Decibel Reader 6. Repeat steps 3-5 until all materials have been used. 7. Mass the objects on a scale then measure them with a ruler to calculate their volume. Use these measurements to find the density. The greater the density the more sound an object would stop. It was thus predicted the cement block would stop the most sound because it was the most dense. The experiment was designed to see if density has an effect on the propagation of sound through a medium. This could be used to find an optimum density for sound-reduction purposes. Materials ComputerWood Foam Insulation PlywoodScale Tone Generating Software Cement BlockRuler/Meter Stick Decibel Reader Rubber Paver Data Conclusion The hypothesis was that the more dense a material was, the better it would be at reducing the sound intensity. Because of this, it was hypothesized that the cement would be the best sound barrier. Although the null hypothesis (that there would be no significant change) was statistically disproved, the data did not support the hypothesis. The two woods were the best sound barriers despite being much less dense than the rubber or cement. This is most likely due to differences in molecular structure. If the molecules in wood were farther apart, then it would be harder for sound to go through. Being more porous than cement meant that it could disperse sound energy better than cement. Another effect could have been the ability to turn more of the energy into heat. Some molecules vibrate in such a way that they efficiently convert sound into heat through friction. This could also have made the wood better at blocking sound than the cement. Photos taken by Matthew Van Beek All tables, Charts, graphs and images are created by Matthew van beek Data Analysis ControlPlywoodWoodCementRubberFoam Decibel90.072.375.278.077.785.9 Density (g/mL)0.000.570.492.311.110.03 Sound Intensity (Watts/m 2 ) 1.00 E-03 1.70 E-05 3.31 E-05 6.31 E-05 5.89 E-05 3.89 E-04 dB Change0.017.714.812.012.34.1 Sound Intensity Relative Change 1.0058.930.215.817.02.57 ControlPlywoodWoodCementRubberFoam Decibel90.272.374.778.076.385.1 Density (g/mL)0.000.570.492.311.110.03 Sound Intensity (Watts/m 2 ) 1.05 E-03 1.70 E-05 2.95 E-05 6.31 E-05 4.27 E-05 3.24 E-04 dB Change0.017.915.512.213.95.1 Sound Intensity Relative Change 1.0061.735.516.624.53.24 ControlPlywoodWoodCementRubberFoam Decibel90.370.574.279.476.485.6 Density (g/mL)0.000.570.492.311.110.03 Sound Intensity (Watts/m 2 ) 1.07 E-03 1.12 E-05 2.63 E-05 8.71 E-05 4.37 E-05 3.63 E-04 dB Change0.019.816.110.913.94.7 Sound Intensity Relative Change 1.0095.540.712.324.52.95 Sound Results for 100 Hz Test Sound Results for 1000 Hz Test Sound Results for 10000 Hz Test The results for each frequency were very similar. In extreme cases sound intensities only shifted about 1-2 decibels. However, the most important information in the context of building materials is the 100 Hz data (because higher frequency sounds don't travel very well in the atmosphere). The data suggests that the two types of wood (plywood and normal) were the best at reducing the sound intensities. The plywood reduced the sound by 17.7 decibels, 17.9 decibels, and 19.8 decibels. The wood was also successful. It lowered the sound by 14.8 decibels, 15.5 decibels and 16.1 decibels. A one-way (unstacked) ANOVA was run comparing each barrier at each frequency. Each found a P value of 0. This shows there is a significant change in the data as a result of the different barriers. The data points pictured from left to right are: Control, Foam, Wood, Plywood, Rubber, and Cement. Tone Generator Software Decibel Reader Rubber Barrier Foam Barrier Wood Barrier