Low-Frequency, Open, Sound-Insulation Barrier by Two Oppositely Oriented Helmholtz Resonators.

Yi-Jun Guan,Hong-Xiang Sun,Xiao-Jun Liu,Yong Ge,Shou-Qi Yuan

doi:10.3390/mi12121544

Abstract

In this work, a low-frequency, open, sound-insulation barrier, composed of a single layer of periodic subwavelength units (with a thickness of λ/28), is demonstrated both numerically and experimentally. Each unit was constructed using two identical, oppositely oriented Helmholtz resonators, which were composed of a central square cavity surrounded by a coiled channel. In the design of the open barrier, the distance between two adjacent units was twice the width of the unit, showing high-performance ventilation, and low-frequency sound insulation. A minimum transmittance of 0.06 could be observed around 121.5 Hz, which arose from both sound reflections and absorptions, created by the coupling of symmetric and asymmetric eigenmodes of the unit, and the absorbed sound energy propagating into the central cavity was greatly reduced by the viscous loss in the channel. Additionally, by introducing a multilayer open barrier, a broadband sound insulation was obtained, and the fractional bandwidth could reach approximately 0.19 with four layers. Finally, the application of the multilayer open barrier in designing a ventilated room was further discussed, and the results presented an omnidirectional, broadband, sound-insulation effect. The proposed open, sound-insulation barrier with the advantages of ultrathin thickness; omnidirectional, low-frequency sound insulation; broad bandwidth; and high-performance ventilation has great potential in architectural acoustics and noise control.

Highlights

It was worth noting that the corresponding reflectance was only about 0.26, indicating that most of the sound energy was absorbed by the barrier
We demonstrated that the sound insulation of the open barrier arose from both sound reflections (Figure 2b) and sound absorptions by the excited mode, and the absorbed sound energy propagating into the central cavity was greatly reduced by the viscous loss in the channel
We found that the transmittances were lower than 0.2 in the range 114.5–138.6 Hz, showing the fractional bandwidth of 0.19

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Low-frequency sound insulation has always been a hotspot in the fields of acoustics and mechanical engineering due to its extensive applications in noise control, environmental protection, and architectural acoustics. Micro-perforated structures [3,4] are used to realize sound absorption, but their thicknesses are comparable to sound wavelengths, leading to relatively large sizes of absorbing structures. The emergence of metamaterials [5–14] and metasurfaces [15–22] have provided the feasibility to overcome the restrictions of these conventional materials of sound, and have been introduced to design several types of units of sound absorption

Methods

Results

Conclusion