Sound Absorption Coefficient Of Some Selected Acoustical Materials

ABSTRACT

Noise has been defined as an unwanted signal. Sound noise is a major societal problem, whose health, environmental and even economic impact is very important. According to the World Health Organization (WHO), noise is an acoustic phenomenon that produces an uncomfortable hearing sensation. Populations whose buildings are housed in areas at high risk of noise are exposed to multiple diseases resulting from noise pollution. To remedy this, it is important to think of choosing the right materials with higher acoustic absorption coefficient. The materials studied in this article are concrete, mortar, stabilized soil, which are commonly and most used materials in the construction of residential buildings. Absorption is one of the most commonly used parameters in linear acoustics. It is well known that the absorption for any material will differ when the properties of the material change. These properties include: thickness, density, flow resistivity, method of mounting, etc. Previous studies have shown that the results for an absorption coefficient test are dependent on the testing method, that is, the absorption coefficients of the same material with the same properties will vary depending on the testing method. The materials studied in this article are concrete, mortar, stabilized soil, which are commonly and most used materials in the construction of residential buildings. The present work consists of determining the sound absorption coefficient of each material indexed by the Kundt tube method in order to provide building technicians with the standards to be followed to improve the acoustic comfort of residential buildings. From the results obtained in this paper, it’s obvious sound absorption coefficients peaks in the low frequencies between 100 Hz and 500 Hz for the three materials. These sound absorption coefficients peaks are accented respectively at 0.74 for the stabilized earth; 0.85 for mortar and 0.94 for concrete.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1    BACKGROUND OF THE PROJECT

• PROBLEM STATEMENT
• OBJECTIVE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• SCOPE OF THE PROJECT
• LIMITATION OF THE PROJECT
• METHODOLOGY
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

• OVERVIEW OF ACOUSTIC MATERIAL
• HISTORICAL BACKGROUND OF ACOUSTIC MATERIALS
• PROPERTIES OF ACOUSTIC MATERIAL
• USES OF ACOUSTIC MATERIAL
• ACOUSTIC MATERIALS AVAILABLE IN MARKET
• MOST COMMON APPLICATION AREAS OF ACOUSTIC MATERIAL
• MEASURES OF ACOUSTICAL MATERIALS EFFECTIVENESS

CHAPTER THREE

METHODOLOGY

• PRESENTATION OF SOME MATERIALS
• MEASURING THE SOUND ABSORPTION COEFFICIENT USING THE KUNDT TUBE
• METHOD USED TO DETERMINE THE ACOUSTIC ABSORPTION COEFFICIENT

CHAPTER FOUR

4.0   RESULT AND DISCUSSION

CHAPTER FIVE

• CONCLUSION
• REFERENCES

Acronyms

• TWA—Time Weighted Average
• TL— Sound Transmission Loss
• dB — Decibel
• NRC— Noise Reduction Coefficient
• STC— Sound Transmission Class

CHAPTER ONE

1.0                                                        INTRODUCTION

1.1                                           BACKGROUND OF THE STUDY

Acoustical materials are a variety of foams, fabrics, metals, etc. used to quiet workplaces, homes, automobiles, and so forth to increase the comfort and safety of their inhabitants by reducing noise generated both inside and outside of those spaces. Acoustical materials are used in two major ways: as soundproofing, by which noise generated from outside a given space is blocked from entering the space; and, as sound absorbing, where noise generated within a space is reduced inside the space itself. As an example of soundproofing, a school might construct a special wall to isolate the music room from a general classroom next door. As for sound absorbing, a machine shop might install barriers to block and absorb the acoustic energy of a noisy air compressor.

Sound and noise are managed by four methods: blocking, absorbing, diffusing, and isolating.

• Blocking relates to the use of soundproofing.
• Absorption works by converting sound energy into heat.
• Diffusion seeks to scatter sound without deadening a room.
• Isolating is done at the source of the noise itself, by placing a compressor on isolation mounts, for instance.

Acoustic absorption refers to the process by which a material, structure, or object takes in sound energy when sound waves are encountered, as opposed to reflecting the energy. Part of the absorbed energy is transformed into heat and part is transmitted through the absorbing body. The energy transformed into heat is said to have been ‘lost’.

When sound from a loudspeaker collides with the walls of a room part of the sound’s energy is reflected, part is transmitted, and part is absorbed into the walls. Just as the acoustic energy was transmitted through the air as pressure differentials (or deformations), the acoustic energy travels through the material which makes up the wall in the same manner. Deformation causes mechanical losses via conversion of part of the sound energy into heat, resulting in acoustic attenuation, mostly due to the wall’s viscosity. Similar attenuation mechanisms apply for the air and any other medium through which sound travels.

The fraction of sound absorbed is governed by the acoustic impedances of both media and is a function of frequency and the incident angle (Parker Barry, 2009). Size and shape can influence the sound wave’s behavior if they interact with its wavelength, giving rise to wave phenomena such as standing waves and diffraction.

Acoustic absorption is of particular interest in soundproofing. Soundproofing aims to absorb as much sound energy as possible converting it into heat or transmitting it away from a certain location.

In general, soft, pliable, or porous materials serve as good acoustic insulators – absorbing most sound, whereas dense, hard, impenetrable materials  reflect most.

However, the noise produced by industries, streets, construction sites, garages, handling sites, individuals or groups of individuals, and even aircraft become more troublesome or even harmful for to neighboring people according to the level where they are located. Indeed, the ear is adversely affected by noise level greater than 120 dB (decibels). This can lead to rupture of the eardrum [2]. As such, inhabitants of buildings located in the vicinity of the endless sources of noise are constantly exposed to unpleasant acoustic effects that will lead sooner or later diseases. To remedy this, it urges to think about the choice of the appropriate materials with a significant acoustic coefficient to ward off the harmful effects caused by sound rumors over the health of the population, during the construction of residential buildings in areas with high risk of noise.

For any building, contractors must check the standards on insulation against aerial noises and shock-related noises, insulation of facades, noise produced by technical equipment or reduction of some local reverberation [3-5].

In a room, how well a room absorbs sound is quantified by the effective absorption area of the walls, also named total absorption area. This is calculated using its dimensions and the absorption coefficients of the walls which is the focus of this work.

1.2                                                  PROBLEM STATEMENT

No one enjoys noise in any form. In the area of the building, noise from traffic, walking, conversation, equipment are the sources of annoyances that can go from a deterioration in the quality of life to direct effects on the health of occupants. As such, the fight against noise is an important issue which translates into regulations, acoustic standards that set minimum acoustic performance expected inside the buildings so as to provide the acoustic comfort for the occupants and users.

1.3                                                     AIM OF THE STUDY

This study was carried out to determine the sound absorption coefficient of some selected acoustic materials.

1.4                                           SIGNIFICANCE OF THE STUDY

This study is used to identify local materials with significant acoustic coefficients that can be used to improve the acoustic comfort of residential buildings.

This research work will throw more light on the best techniques for absorbing noise most especially in a room. This study will also be designed to be of immense benefit to all builders and residents of any building.

1.5                                                   SCOPE OF THE STUDY

This study was carried out to determine the sound absorption coefficient of some selected acoustical materials. The materials selected in this study are concrete, mortar, stabilized soil, which are commonly and most used materials in the construction of residential buildings. The present work consists of determining the sound absorption coefficient of each material indexed by the Kundt tube method in order to provide building technicians with the standards to be followed to improve the acoustic comfort of residential buildings. From the results obtained in this paper, it’s obvious sound absorption coefficients peaks in the low frequencies between 100 Hz and 500 Hz for the three materials. These sound absorption coefficients peaks are accented respectively at 0.74 for the stabilized earth; 0.85 for mortar and 0.94 for concrete.

1.6                                                        LIMITATION OF THE STUDY

As we all know that no human effort to achieve a set of goals goes without difficulties, certain constraints were encountered in the course of carrying out this project and they are as follows:-

Difficulty in information collection: I found it too difficult in laying hands of useful information regarding this work and this course me to visit different libraries and internet for solution.

Financial Constraint:        Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).

Time Constraint:   The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work

1.7                                             RESEARCH METHODOLOGY

In the course of carrying this study, numerous sources were used which most of them are by visiting libraries, consulting journal and news papers and online research which Google was the major source that was used.

1.8                                     PROJECT ORGANISATION

The work is organized as follows: chapter one discuses the introductory part of the work,   chapter two presents the literature review of the study,  chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.