Design of a Scaled Down Acoustic Experiment with Anechoic and Reverberation Chambers
Creators:Ricciardi, Eric D.
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Mechanical and Aerospace Engineering Honors Theses; 2013
The focus on this research is to design and evaluate a split chamber that can be used for measuring random incidence properties of acoustic materials and achieve reliable results for frequencies larger than 500 Hz. A split chamber consists of an anechoic section and a reverberant section; therefore the sound field in each portion must be designed to simulate direct and diffuse field conditions in the far field. The challenge in this test chamber design is adhering to small scale dimension constraints of 2.4m x1.2m x 1.2m and a maximum cost of \$1000, while maintaining a certain level of performance in terms of lowest frequency that can be characterized. By analyzing both acoustical field theory and absorption characteristics this chamber is found to have a cutoff frequency of approximately 570 Hz. The far field sound pressure distribution in the reverberant chamber was determined to be sufficiently uniform, both in the room and across the panel. Sound pressure measurements in the anechoic chamber correlated well to the inverse square law, given by ideal direct field conditions. The noise reduction of the room to the outside ranged from 27 dB to 40 dB across the designed frequency range, which indicates that the chamber is sufficiently sealed from the ambient sound. The chamber was built to be within the sizing constraints and met a final construction cost under \$1000. This split chamber will be used to assist in student projects and as a teaching tool for mechanical engineering courses. Future work on this project will consider the addition of diffusers in the reverberant chamber; this study will be done using boundary element modeling software and experimental measurements.
Related Item:Academic Major: Mechanical Engineering
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