Date on Master's Thesis/Doctoral Dissertation
Committee Co-Chair (if applicable)
Cohn, Robert W.
Noise barriers; Noise control
Noise reduction testing is completed for two single steel plate constructions with different thicknesses and for two double wall constructions with different air gap thicknesses that include the same two plates used in the single plate constructions. Results compare favorably with known theory and experimental results from previous literature. These favorable comparisons include the direct relationship between mass per unit area and transmission loss for single plate constructions, the presence of a noise reduction valley near the mass-air-mass frequency, the dependency of the mass-air-mass frequency on the air gap thickness, and the existence of a bridge frequency. Despite the similarities between theory and experimental results, there are discrepancies. Both the mass-air-mass and bridge frequencies for the double wall constructions were over predicted by equations offered in the literature. Additionally, the theory over predicted the bridge frequency, and the bridge frequency did not shift with changing air gap thickness. To uncover if these discrepancies are a result of structural dynamics not accounted by theory, experimental modal analysis was conducted on the single and double plate constructions. Investigation into the mode shape behavior reveals that the double wall noise reduction minimum attributed to the mass-air-mass frequency occurs in a region containing mode shapes where the two plates display synchronous motion and an unexpected noise reduction peak occurs in a frequency region where the double wall construction mode shapes exhibit asynchronous motion. Finally, acceleration plots of the constructions when excited by sound reveals that the bridge frequency occurs at a transition when the plate vibration reduces significantly.
Phillips, Richard Michael 1988-, "Investigation of transmission loss through double wall structures with varying small air gaps using modal analysis." (2014). Electronic Theses and Dissertations. Paper 1760.