on the study of the acoustic performance of the seminar halls nurul

on the study of the acoustic performance of the seminar halls nurul
ON THE STUDY OF THE ACOUSTIC PERFORMANCE OF
THE SEMINAR HALLS
NURUL HAMIZAH BINTI MOHAMED
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
i
ON THE STUDY OF THE ACOUSTIC PERFORMANCE OF
THE SEMINAR HALLS
NURUL HAMIZAH BINTI MOHAMED
This report is submitted in fullfillment of the requirement for the award
Bachelor of Mechanical Engineering ( Design & Innovation)
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
DISEMBER 2014
ii
DECLARATION
“I hereby declare that the work in this report is my own except for summaries and quotations
which have been duly acknowledged.”
Signature:
...................................
Author:
Nurul Hamizah Mohamed
Date:
...................................
iii
SUPERVISOR DECLARATION
“I hereby declare that I have read this thesis and in my opinion this report is sufficient in
terms of scope and quality for the award of the degree of
Bachelor of Mechanical Engineering (Design & Innovation)”
Signature:
...................................
Supervisor:
Assoc. Prof. Dr Azma Putra
Date:
...................................
iv
For my left shoulders:
Mohamed Mahat
Nor’ashikin Kasbi
Nurul Hasyimah Mohamed
Nurul Hazwani Mohamed
Muhammad Ammar Ashraf Mohamed
and
the right shoulder
v
ACKNOWLEDGEMENT
First and foremost, I would like to express my sincere gratitude to my supervisor,
Assoc Prof. Dr Azma Putra. Without fail, he has provided me details guidance and
encourages me throughout the project. He has always been enthusiastic in solving, reflecting,
responding and advising my problems. I appreciate for the countless time he had spent having
discussion with me regarding my final year project and offering numerous suggestion to
improve my work.
Secondly, I would like to acknowledge and give appreciation to a senior, Dg Hafizah
Kassim, for giving suggestions, sharing knowledge and provide guidance throughout the
project, mostly on modelling and analyzing using CATT Software. Her knowledge has
helped me a lot on completing this project.
Special thanks go to my parents and families for their good-natured forbearance with
the process and for their pride in this accomplishment. My gratitude is for their
understandings of my busy life and pack schedules.
My gratitude are also go to The Saujanas: Siti Masyita Noraziman, Nabilah Zafirah
Jantan, Amira Khalida Mohd Nasir, Noor Asekin Md Yasukin, Nur Haziqah Mohd Ruzmi,
Nurul Asyilah Zakaria and Nurul Jannah Baharuddin, who always dedicate me moral support
and ideas on solving problems and sharing knowledge. Their kindness has built me up to be a
strong and dedicated person. Nevertheless, thanks to my course-mates and friends for their
support, patience, encouragement and useful suggestions.
vi
ABSTRACT
A seminar is generally, a form of academic instruction, either at an academic institution
or offered by a commercial or professional organization. While listening to a speech, a clear
sound is a very important. Clear sound will directly affect the listener’s attention. A person
who develops skills in poor acoustic environment may develop long-term speech
comprehension problems. Loud and noisy environment will tend to make the audience loss
focus and the interest to learn. The noise and reverberation is also can inhibit the reading and
spelling ability, behavior, attention, concentration and academic performance. In this
research, the study of the acoustic performance of halls will be the main part of the projects.
To narrowing the research, two Seminar Halls in UTeM have been chose to be the examples.
The halls are Dewan UTeM 1 and Dewan Besar UTeM. This is because the reflection and
refraction of sounds can be influenced by the materials used. Reinforcement system brings so
much outputs of humming, buzzing, vibration and echoes. This study will helps on giving
result of good acoustic performance in the way to give best decision for the architects to
either choose the correct materials in building or else, allocate absorbers in the right position.
vii
ABSTRAK
Seminar umumnya merupakan satu bentuk pengajaran akademik , sama ada di institusi
akademik atau ditawarkan oleh organisasi komersial atau profesional . Semasa mendengar
ucapan seminar, bunyi yang jelas adalah sangat penting . Bunyi yang jelas secara langsung
boleh menjejaskan perhatian pendengar . Seseorang yang berada dalam persekitaran akustik
yang lemah boleh meningkatkan masalah pertuturan kefahaman. Persekitaran yang kuat dan
bising akan cenderung kepada pendengar untuk hilang tumpuan dan minat untuk belajar.
Bunyi dan gema juga boleh menghalang bacaan dan kebolehan ejaan, tingkah laku, perhatian,
tumpuan dan prestasi akademik . Dalam kajian ini , prestasi akustik dewan akan menjadi
bahagian utama projek . Sebagai bahan penyelidikan , dua Dewan Seminar di UTeM telah
dipilih iaitu Dewan UTeM 1 dan Dewan Besar UTeM . Bahan-bahan dinding , lantai dan
siling dewan merupakan subjek utama yang akan dikaji dalam kajian ini . Ini kerana pantulan
dan pembiasan bunyi boleh dipengaruhi oleh bahan-bahan yang digunakan. Sistem yang
biasa digunakan membawa begitu banyak output bersenandung, bergetar dan bergema .
Kajian ini akan membantu dalam kajian memberikan hasil prestasi akustik yang baik dengan
cara yang memberi keputusan terbaik bagi arkitek untuk memilih bahan-bahan yang betul
dalam pembinaan bangunan atau dalam pemasangan penyerap bunyi di kedudukan yang
betul.
viii
TABLE OF CONTENT
TOPIC
CHAPTER 1
CHAPTER 2
PAGE
TITLE PAGE
i
DECLARATION
ii
SUPERVISOR DECLARATION
iii
DEDICATION
iv
ACKNOWLEDGEMENT
v
ABSTRACT
vi
ABSTRAK
vii
TABLE OF CONTENTS
viii
LIST OF FIGURES
x
LIST OF SYMBOLS
xiii
INTRODUCTION
1.1 Background
1
1.2 Problem Statement
2
1.3 Objectives
3
1.4 Scope
3
LITERATURE REVIEW
2.1 Introduction
4
2.2 Sound Absorption
5
2.3 Reverberation Time
6
2.4 Speech Intelligibility
9
2.5 Rapid Speech Transmission Index
10
2.6 Early Decay Time
11
2.7 Clarity
12
2.8 Early Energy Fraction
13
ix
CHAPTER 3
METHADOLOGY
3.1 Flow Chart
14
3.2 Seminar Halls
15
3.3 Modeling
3.3.1 CATT Acoustic
17
3.3.2 Point Declaration
18
3.3.3 Planes Production
19
3.3.4 Coefficient of Absorption
20
3.4 Analyzing
3.4.1 Source and Receiver
3.5 Validation Experiment
21
3.5.1 Sound Level Meter
23
3.5.2 Experimental Source and Receiver
23
3.6 Summary
CHAPTER 4
20
24
RESULTS AND DISCUSSION
4.1 Dewan UTeM 1
25
4.1.1 Reverberation Time
27
4.1.2 Clarity
29
4.1.3 Early Energy Fraction
31
4.2 Dewan Besar
32
4.2.1 Reverberation Time
32
4.2.2 Clarity
36
4.2.3 Early Energy Fraction
37
4.3 Suggestion on Improving The Acoustic Performance
CHAPTER 5
4.3.1 Dewan UTeM 1
38
4.3.2 Dewan Besar
41
CONCLUSION AND RECOMMENDATION
44
REFERENCES
46
APPENDICES
x
LIST OF FIGURES
FIGURE
TITLE
2.1
Frequency Range of Typical Sound Source (Everest &
PAGE
5
Pohlman, 2009)
2.2
2.3
The Ray Path of the Reflection and Absorption of Sound
(Crandall, 1926)
Graph of Reverberation Time by Taking Sound Level versus
6
8
Time (Grade et al, 2001)
2.4
The Variation of Optimum Reverberation Time with Volume
9
(Noise Pollution and Its Control, 1989)
2.5
Qualitative Interpretation of RASTI (Sound System
11
Equipment Part 16).
3.1
The Flow Chart of Methodology
14
3.2
Interior Part of Dewan UTeM 1
16
3.3
Interior Part of Dewan Besar
17
(a) Views from right
(b) Views from left
(c) Views fom back
3.4
Logo of CATT Acoustic
18
3.5
The management of Point from Each Axis
18
3.6
Declaration of each point for Dewan UTeM by using CATT
19
Software
3.7
Declaration of Planes of Dewan UTeM 1 by using CATT
19
Software.
3.8
Declaration of Coefficient of Material Absorption of Dewan
20
UTeM 1 by using CATT Software
3.9
Declaration of the Sources for Dewan UTeM 1 by using
CATT Software.
21
xi
3.10
Declaration of the Receivers for Dewan UTeM 1 by using
21
CATT Software
3.11
Measurement setup for the Validation Experiment
22
3.12
SLM set in the experiment:
23
(a) SLM is calibrated before used.
(b) SLM being put on 1.2m tripod stand
3.13
The points of Reverberation Time in Experiment
24
4.1
The Model of Dewan UTeM 1:
26
(a) views from sides of the hall
(b) views from the floor of the hall
4.2
The Reverberation Time of Receivers in Dewan UTeM 1
27
4.3
27
4.4
The Optimum Reverberation Time Graph Depends on The
Room Volume for 500Hz Octave Sound. [14]
The Experimental Reverberation Time of Dewan UTeM 1
4.5
The Clarity of Dewan UTeM 1
30
4.6
The Division of the Receivers in Dewan UTeM 1
30
4.7
The Early Energy Fraction of Dewan UTeM 1
31
4.8
Model of Dewan Besar UTeM:
33
29
(a) views from the side of the hall
(b) views from the below of the hall
4.9
The Reverberation Time of Dewan Besar
34
4.10
The Reverberation Time for The Receiver That Be Sitting on
35
Stage
4.11
The Distribution of Early Energy Fraction of Receiver That
36
Sit on Stage
4.12
Figure 4.12: The Distribution of Clarity in Dewan Besar
36
4.13
Figure 4.13: The Distribution of Early Energy Fraction in
37
Dewan Besar.
xii
4.14
Soundboard Set on Dewan UTeM 1 Ceiling
38
4.15
The Acoustic Performance of Dewan Utem 1 with
39
Soundboard as Absorber
4.16
Graph of Difference RT Before and After Soundboard
39
Installation
4.17
Carpet is attached on Dewan UTeM 1 Floor
40
4.18
The Acoustic Performance of Dewan UTeM 1 with Carpet as
40
Absorber
4.19
Graph of Difference RT Before and After Carpet Installation
41
4.20
Nylon Cloth attached to hall ceiling
42
4.21
Result of attaching Nylon Cloth at the hall ceiling.
42
4.22
Figure 4.22: Glass Fence Attached on the Stage
43
4.23
Result of attaching Glass Fence on stage
43
xiii
LIST OF SYMBOLS
FIGURE
TITLE
RT
Reverberation Time
V
Volume of Rooms in m3
S
Total surface area of room in m2
Α
Average of Coefficient of Material Absorption of the
room surfaces
E(t)
Early Decay Time (EDT)
p
Impulse response
τ
Early Limit of Sound
C
Clarity
D
Early Energy Fraction
CHAPTER 1
INTRODUCTION
1.1
BACKGROUND
A speech is a method of delivering messages, knowledge or lectures. In delivering a
speech, most all the activities involve speech between the source (deliver) and the
receivers. While listening to a speech, a clear sound is a very important. Clear sound will
directly affect the listener’s attention. According to Smaldino & Crandell (1999), a
person who develops skills in poor acoustic environment may develop long-term speech
comprehension problems.
In a classroom, as example, loud and noisy environment will tend to make the
students loss focus and the interest to learn. The noise and reverberation is also can
inhibit the reading and spelling ability, behavior, attention, concentration and academic
performance. Hence, classrooms and lecture halls are also important, often neglected, to
have a perfect acoustic performance to make sure the speech can be delivered smoothly
and correctly.
2
In this research, the study of the acoustic performance of lecture halls will be the
main part of the projects. To narrowing the research, two Seminar Halls in UTeM have
been chose to be the specimens. The halls are Dewan UTeM 1 and Dewan Besar UTeM.
The materials of the walls, floors and tops of the halls are the main subject to be
examined in this study. This is because the reflection and refraction of sounds can be
influenced by the materials used.
On the same time, most of the lecture halls, in huge or small size, are using
reinforcement system. Reinforcement system is where combination of tools used to
make the sound can be heard in every side of the hall. Addition of tools like
microphones, signal processors, amplifiers and loudspeakers will help to make the voice
louder. Sometimes, connection of too many reinforcement tools will bring the outputs of
humming, buzzing, vibration and echoes. Hence, the factor of getting the clear sound is
neglected.
This study will helps on giving result of good acoustic performance in the way to
give best decision for the architects to either choose the correct materials in building or
else, allocate absorbers in the right position.
1.2
PROBLEM STATEMENTS
Audience of a speech cannot give full commitment when listening to the
presenter as the sound is having echoes and humming. This problem is actually plays a
big role on distracting them to start ignoring and neglecting the speaker. In Dewan
UTeM 1 and Dewan Besar UTeM, the reinforcement system brings the echoes and
humming during speaker is giving the speech. In Dewan Besar moreover, audiences that
sit on the stage are having problem to listen to the speech. Thus, the audience feels
uncomfortable with the noisy situations.
3
1.3
OBJECTIVES
1. To model and simulate the acoustic performance of Dewan UTeM 1 and Dewan
Besar UTeM using CATT software.
2. To suggest the solutions on improving the acoustic quality of the halls.
1.4
SCOPE
This research will only focus on the experimental of acoustic performance of the
Seminar Hall by using CATT software. Modelling the shape of the hall will be done as
the first step before any analyzing works take place. Measurement of the perimeter of
the hall and the material used is noted on modelling the hall inside the software. The
project also intends to find the result of the clarity of speech and the reverberation time
of the sound waves.
The audience area will be set on the floor, and will be labelled in 5 different
coordinates. This is to make sure that the performance of the sound will be tested in
different points of the hall. Source will be located at where the microphone is always set.
The results will then being interpreted and finding solution on how to improve
the acoustic quality will be doing. These solutions will be suggested to make sure the
sound can be heard clearly and the performance can increase the audience interest.
CHAPTER 2
LITERATURE REVIEW
2.1
INTRODUCTION
Every day we are exposed to sound either is not required, necessary or beneficial
for almost twenty-four hours a day, seven day a week. Sound is a vibration that
propagates as a typical audible mechanical wave of pressure and displacement, through a
medium such as air or water. Sound wave that travels through air is the resulting of the
physical disturbance of air molecules such when tapping a tuning fork and the waves
will combine to reach the listener direct or indirectly (Crandall, 1926).
In a general way, the sound wave is any disturbance that transmitted in an elastic
medium consisting of gas, liquid or solid (Tong & Wong, 2001). In physical way, there
was no different between sound and noise. Actually, sound is sensory perception by
human (Mechel et al, 2002) which it is can be detected by the human ears (Everest &
Pohlman, 2009).
5
Although sound travels and can be heard but not all sound is audible. Limits of
audibility for humans are only between 20Hz to 20 kHz (Charles, 1998). Sound below
20Hz is infrasonic and sound greater than 20 kHz is called an ultrasonic sound.
Figure 2.1: Frequency Range of Typical Sound Source (Everest & Pohlman, 2009).
Decibel or dB is the most common unit of sound measurement (Charles, 1998).
The threshold of hearing is considered to be 0dB and the range sound for normal human
experience is 0dB to140dB.
2.2
SOUND ABSORPTION
Sound absorption refers to a material, structure or object absorbing sound energy
when sound waves collide with it, as opposed to reflecting the energy. Every material
has its own ability to absorb sound energy. Materials that have low absorption ability
tend to reflect most of the acoustical energy.
Sound absorption is a capability of a material to convert sound energy into other
energy. Sound energy usually converted to heat energy. Part of the absorbed energy is
6
transformed into heat and part is transmitted. The energy transformed into heat is said to
be lost.
The property of material absorbing ability is called Sound Absorption
Coefficient. To find the coefficient, architect usually used the Noise Reduction
Coefficient (NRC). If the scale of NRC is 1.0, that mean that the material is perfectly
absorptive and if it is 0.0, it is a reflective materials (Crandall, 1926). This coefficient
helps the work on choosing the right material for each building walls.
Figure 2.2: The Ray Path of the Reflection and Absorption of Sound (Crandall, 1926)
2.3
REVERBERATION TIME
When a sound is triggered or generated in a room, many things will happen in a
blink of eye. The reflecting boundaries of the room will result repeated reflections which
determine the rapid establishment of more or less uniform sound field. And this field
then decays as the sound energy is absorbed by the bounding materials. The reflecting
surface with its absorptive ability will determine the rate of the sound energy decays.
And time taken for the sound intensity to decays for 60 dB is called the “Reverberation
Time” (Grade et al, 2001).
The Reverberation Time is an important part as a quantity for characterizing the
acoustic properties of a room. When building a room, the first step in architectural
7
acoustic design is to identify the good values of the reverberation time depends on the
function of the room. Furthermore, we can specify the materials that to be used in the
construction which will achieve the desired value of the Reverberation Time.
For an example, a classroom should have the reverberation time in the range of
0.4 to 0.6 seconds. But in reality, many did not manage to achieve the suitable
reverberation time and having reverberation time of 1 second and more. In such reality
cases, teachers have to compete against the lingering reflection of his or her own voice
to get the student’s attention. The result is a chaotic jumble of sound (Goelzer &
Hansen).
In 1922, a pioneer in the study of room acoustics, Wallace Sabine came up with
the formula which is defined as Eq. (1) below,
RT  0.16m 1
V
S
(1)
The equation above show that the RT is the reverberation time, where V is for
the room volume in m 3 , S will be the total surface area in m 2 , and  is the average of
the absorption coefficient of room surfaces.
The formula is based on the volume of space and the total amount of absorption
within a space. The total amount of absorption within a space is referred as “Sabins”
where the product of S is the total absorption in Sabins.
8
Figure 2.3: Graph of Reverberation Time by Taking Sound Level versus Time
(Grade et al, 2001)
The graph above show of RT60 where T is defined as the duration required for
the space-averaged sound energy density in an enclosure to decrease by 60 dB after the
source emission has stopped (Grade et al, 2001). Things that will be effect
reverberation are size of space and the amount of reflective or absorptive surface within
space (Goelzer & Hansen). A space with high absorptive surface will absorb the sound
and stop it from reflecting back into the space (Grade et al, 2001). Reflective surfaces
will reflect sound and increase the reverberation time within space. Therefore, a large
space will need more absorption instead of reflection in the way to achieve the same
reverberation time as a smaller space.
In general, the best reverberation times are less than 1 second for speech and
longer than 1 second for music. Short reverberation times are necessary for clarity of
speech; otherwise, the continuing presence of reverberant sound will mask the following
sound and cause the speech to be blurred. Longer reverberation times are considered to
enhance the quality of music, which will give “dead” environment if the reverberation
time is too short. Larger rooms are judged to require longer reverberation times, as is
also the case with lower frequencies of sound.
According to Berg and Stork on their research in 1995, the best RT for a speech
should be less than 1 second at frequency band of 500Hz and below (Bies & Hansen,
9
1996). The reverberation time of a room must be suitable to the function and volume of
the room, should apply for sound frequency from 125Hz to 4,000Hz.
Figure 2.4: The Variation of Optimum Reverberation Time with Volume
(Noise Pollution and Its Control, 1989)
2.4
SPEECH INTELLIGIBILITY
Speech intelligibility is defined as a percentage of speech or words heard
correctly by the listeners. It is a vital element of human communication. Without
outstanding speech intelligibility, communication is hampered. Good intelligibility is
influenced by reverberation time (RT), background noise and distance of the listener
from the speaker. From the three elements, RT and background noise are influenced by
the architecture of the room; therefore, they should be given greater attention at the
design stage. However, the quality of speech is also dependent on vocal strength or
power, dialect and clarity of the spoken words.
From Noxon in his research in 2002 highlighted that in the draft version of the
new ISO 9921 standard on the “Assessment of Speech Communication” defined speech
intelligibility as “a measure of effectiveness of understanding speech”. The measurement
is usually expressed as a percentage of a message that is understood correctly. Speech
intelligibility does not imply speech quality. Speech intelligibility is related to the
amount of speech items that are recognized correctly, while speech quality is related to
10
the quality of a reproduce speech signal with respect to the amount of audible
distortions. Thus, a message that lacks quality may still be intelligible.
Speech intelligibility in the hall is a crucial aspect when talk or lecture is given.
The non-uniform distribution of the intelligible speech was due to the impaired direct
path of the sound from the speaker (Amasuomo, 2013). Echoes experienced in the
lecture halls were as a result of the time delay between the arrivals of the initial sound
from the speaker and then reflected sound from the parallel walls. The presence of
echoes in the halls during speech or seminar is a nuisance. Thus, echoes should be
avoided.
2.5
RAPID SPEECH TRANMISSION INDEX (RASTI)
RASTI method is an objective method for rating the transmission quality of
speech with respect to intelligibility (Sound System Equipment Part 16). The method is
intended for rating speech transmission in auditorium, halls and room with or without
the sound reinforcement system. It is economical, and time saving for each station can
be evaluated either in eight, sixteen or thirty two seconds.
Rapid speech transmission index (RASTI) is a simplified version of speech
transmission index (STI). A modulated test signal is fed to a loudspeaker at the talker’s
location. The receiver’s microphone is positioned at the receiver location. The system
gives an accurate read out of the measured RASTI value at the receiver position. RASTI
can also take account of the effects of reverberation, as well as background noise (Sound
System Equipment Part 16).
It tests in only two frequency band with the assumption that the response of the
sound system is more than 100Hz to 8 kHz or higher with a flat frequency response.
Poor designed systems often tend to show a too optimistic measurement. The measured
values were represented by the properly flat systems with the frequency spectrum.
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