Conference Room Reverberation Time Correction Using Helmholtz Resonators Lined with Absorbers

Hossein Namvar Arefi,Peyman Irajizad,Seyyede Mahshid Ghaffari,Shiva Sharifpour,Farhad Ramezanghorbani,Seyyed Mohammad Amin Ghiasi,Seyede Delaram Ghoreishi Langroudi,Ahmad Amjadi

doi:10.1155/2014/472524

Hossein Namvar Arefi, Peyman Irajizad + Show 6 more

Open Access

https://doi.org/10.1155/2014/472524

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Abstract

Echo and sound resonance in a conference room cause obscure speech and make listeners tired. Thus, the acoustical properties of a conference room are vitally important. The conference room 412 at Sharif University Physics Department failed to meet basic acoustical standards. The aim of this research is to improve reverberation time (RT) of the conference room using Helmholtz resonators with defined dimensions, diffusers, and sound absorbers. Helmholtz resonators are widely used to absorb sound noise especially at low frequencies. They are particularly useful when noise has a narrow-frequency band. One of the advantages of using Helmholtz resonators is their capacity to be tuned on different frequencies. We enhanced acoustical properties of Helmholtz resonators using proper absorbers and diffusers. In order to decrease the RT, a large number of Helmholtz resonators have been made and installed in proper positions in the conference room. The RT was measured before and after installation. The measurements indicate that the acoustical characteristics of the conference room have been significantly improved.

Highlights

Helmholtz resonator is an acoustical tool frequently used in applied acoustics
A well-tuned Helmholtz resonator is very useful for attenuating low-frequency noises [6], which makes them useful as low-frequency sound absorbers in large reverberant halls [7]
It is measured in 1/3 octave frequencies before and after the placement of Helmholtz resonators in the conference room

Summary

Introduction

Helmholtz resonator is an acoustical tool frequently used in applied acoustics. Basically it is a cavity that is connected with the outside space through a neck or an opening and collects sound waves within its resonance frequency [1]. Acoustic resonators with sound absorbers efficiently absorb sounds near their resonance frequencies [2]. They have been in widespread use since Ancient Greece [3]. Today they are employed to enhance sound fields in large reverberant spaces such as churches [4] and as mufflers in ducts [5]. Reverberation time (RT) is a temporal parameter to evaluate properness of the acoustical properties in indoor spaces. It is defined as the time required for the sound pressure level to decay by 60 dB [8]. When a sound is reradiated from the resonator’s opening, it tends to spread as a hemisphere; thereby, it diffuses unabsorbed energy and improves sound quality in a studio or listening room [11]

Description and Experiment

Findings

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