Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department/School/Program

Mechanical Engineering

First Advisor

Dr. David W. Herrin

Abstract

The sound absorbers in most common use today are porous materials like fibers and foams. This work examines three alternatives to porous absorbers: microperforated panels, acoustic fabrics, and additively manufactured absorbers. The research is a combination of design, measurement and characterization of their properties, and analysis.

Microperforated panels are thin metallic or plastic panels with sub-millimeter size holes or perforations. Sound absorption can be tuned by adjusting the spacing between the panel and a cavity behind the panel. Several different configurations were considered where the geometry behind the panel was divided up into channels of varying length and cross-sectional area. Results showed that the sound absorption effectiveness could be improved at low frequencies and that the absorber was more effective over a broader range of frequencies. This was demonstrated using both impedance tube measurements and diffuse field sound absorption measurements in a small reverberant room.

Sound absorptive fabrics are similar to microperforated panel absorbers and function using the same principle. Acoustic resistance is high through the fabric due to small holes or the tight weave. If the particle velocity is high in the fabric, the fabric will effectively attenuate sound. The sound absorption is easily tuned by adjusting the distance between the fabric and a hard backing. It is demonstrated that the transfer impedance can be simulated using theory similar to that typically used for characterizing microperforated panel absorbers.

Recently, there has been a great interest in using additive manufacturing to develop sound absorbers. The design space was partially explored by designing absorbers using long perforations, lightweight panels, and Helmholtz resonators with long necks. The sound absorbers are shown to be very effective at low frequencies where conventional sound absorbers like fibers and foams are ineffective.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.456

Funding Information

Funds awarded to the Vibration and Acoustics Lab in which the author was a research assistant.

Funder: Vibro-Acoustics Consortium of Mechanical Engineering Department at University of Kentucky, 2014-2019.

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