Design of noise reduction cavity structures for additive manufacturing

Abstract

Passive acoustic mufflers have a vital role in controlling the transmission of airborne noise passing into the human living environment. The geometry of the air path affects the attenuation of sound due to absorption and reflections of sound waves. Use of simple muffler geometry consumes a larger space for reduction of low frequency noises due to their longer wavelengths. A complex design of air cavity is useful to combine two or more sound absorption mechanisms to effectively reduce low and medium frequency noises in a minimal space. Manufacturing of complex cavity structures are simplified due to advent of additive manufacturing technologies.

A combined study on manufacturability of complex cavity structures and noise reduction performance due to geometric complexity remains relatively an unexplored field. This study aims to develop new designs for noise reduction cavity structures and numerically analyses the sound transmission loss through the cavities. The design rules used in this study incorporate principles of both noise reduction and additive manufacturing.

Study concludes design complexity of cavity a potential parameter that affects performance of passive noise reduction. Compact designs for additively manufacturable mufflers for controlling low and medium frequency noises are unveiled. Multiple expansion structure introduced in the study provides a peak transmission loss of 240 decibels and completely controls the sound less than 50 decibels for medium frequency range from 1000 Hz to 3250 Hz. Use of combination of Helmholtz cavity with multiple expansion structure provides a peak transmission loss of 173 decibels for a frequency of 620 Hz and completely controls the sound less than 50 decibels for a frequency range between 600 Hz to 1000 Hz. Increase of chamber width in multiple expansion structure widens the frequency bandwidth for noise reduction and decreases the peak transmission loss.