1

SUMMARY

of the thesis

SOUND TRANSMISSION THROUGH LIGHTWEIGHT PANELS

Submitted to the

CH. CHARAN SINGH UNIVERSITY, MEERUT

For the Award of the Degree of

DOCTOR OF PHILOSOPHY in

PHYSICS by

DHARM PAL SINGH

Under the Joint Supervision of

Supervisors:

Dr. R. S. UPADHAYAY Dr. MAHAVIR SINGH Associate Professor Principal Scientist Department of Physics, Acoustics, Ultrasonics & Vibration Section D. A. V. PG College, National Physical Laboratory Bulandshahr 203001 (UP) Dr. K. S. Krishnan Road New Delhi 110012

MAY 2012

2

DECLARATION

I (Dharm Pal Singh) hereby declare that the Thesis entitled “Sound

Transmission Through Lightweight Panels” to be submitted for the Degree

of Doctor of Philosophy in Physics is my original work and the Thesis has not

been formed the basis for the award of any degree, diploma, associateship,

fellowship of similar other titles. It has not been submitted to any other

University or Institution for the award of any degree or diploma.

Place: Bulandshahr Signature of the Scholar

Date: May 2012 (Dharm Pal Singh)

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CONTENTS

DECLARATION 2 1 INTRODUCTION 4

2 LITERATURE REVIEW 4

2.1 Studies on Sound transmission prediction models 5

2.2 Material behaviour study of sound transmission 6

2.3 Sound Studies on using agricultural waste in building materials 9

3 OBJECTIVE AND SCOPE OF WORK 9

4 DESCRIPTION OF THE RESEARCH WORK

4.1 Experimental Investigation 10

4.2 Details of transmission loss suite 10

4.3 Details of instrumentation and experiments 11

4.4 Sound reduction index of the TL suite 15

4.5 Measurement of flanking transmission 16

4.6 Evaluation of Sound Reduction Index 17

4.7 Measurement of longitudinal wavespeed (cL) 18

4.8 Measurement of loss factor (η) 18

5 STUDIES ON TRANSMISSION OF SOUND TROUGH

MATERIALS AND BUILDING COMPONENTS

5.1 Material details 19

5.2 Test conditions 20

5.3 Theoretical prediction model using SEA 23

5.4 Real time simulation results using ODEON 26

6 RESULTS AND DISCUSSIONS 27

7 CONCLUSIONS 33

REFERENCES 34

LIST OF PUBLICATIONS 38

4

1. Introduction

Sound transmission in buildings is a problem that exists in many countries

and many different solutions are adopted to achieve acceptable levels of sound

insulation. In recent days usage of light weight building structures are widely used

by construction industry for easier and cost effective method. With the expansion of

real estate activities and newer building materials the need to attend the sound

insulation requirements for both structure borne and airborne sound also assumes

greater dimensions. The problem however is closely associated with several aspects

of building construction, which include its layout, types of materials used in

construction and other building service requirements. Apart from conventional

materials, studies have undergone with the use fibre reinforced ferrocement panels

in the construction. This type of construction exhibits easier and cost effective

optimized solutions. Fibres used with ferrocement panels provide better natural

performance on strength and thermal insulation behavior too. This property

enhances the energy efficient character of the building; nevertheless in an acoustical

sense the studies are not very informative which require deeper investigation.

Annoyance of structure borne and airborne sound are major problems that

are faced by people in buildings. Properly designed and constructed methods will

always provide a comfortable acoustical environment. All significant paths of

transmission must be considered for sound transmission within the building as well

as noise intrusion from outside the building.

2. Review of Literature:

Sound insulation of partitions has been a subject of systematic, scientific

investigation for the last 100 years. The early papers were concentrated on the

infinite walls, as they were easier to treat by analytical methods. The treatment of

finite size walls with cavities were first concentrated on the high frequency range

and statistical description of sound field (the concept of diffuse field) was

employed. The low frequency range was long considered as less important in the

context of building partitions, as the human sensitivity to sound decreases strongly

5

at low frequencies. However, the increased amount and efficiency of sources of low

frequency sound in buildings has drawn the attention of researchers and the

standardization committees to sound transmission. The use of mechanical

ventilation systems, increased amount of household appliances in dwellings,

improved efficiency of stereo systems, and the ever increasing density of traffic, all

contributed to the increase levels of noise in buildings. Some important studies

dealing with transmission of sound through structures are due to Cremer and Heckl

(1984) [10], Lyon and Dejong (1995) [28] and Craik (1998) [8, 9].

2.1. Studies on Sound transmission prediction models:

The sound insulation in buildings has been studied based on prediction

models on the concept of energy balance such as Statistical Energy Analysis (SEA).

This concept has been adopted for enhancing accuracy of sound transmission by

Craik (1982) [5].

Craik, (1998) [8, 9] investigated the structure borne sound transmission in

lightweight buildings using SEA. Reducing the mass as a means of sound

transmission in buildings led to the development of lightweight buildings. A higher

level of sound insulation was achieved by introducing discontinuities whilst

retaining structural integrity. For direct transmission through lightweight partitions

the nature of connection between the lightweight cladding and the frame determines

the nature of structural coupling. The coupling can be modeled as either a series of

point connections or line connections. If flanking transmission was included then

the complexity of model increases.

Vigran, (2010) [40] investigated a simple method to account for the effect of

point- and line-connections in double-leaf constructions in a transfer matrix setup.

To cover the frequency range above the critical frequency of the constituent plates,

some new developments as to the forced radiation from plates were considered. A

number of comparisons had been performed, mainly with the measured sound

reduction index of lightweight double walls with gypsum boards. Cases include

walls with cavity filling as well as with empty (air-filled) cavities. In the latter

6

cases, the energy losses of the cavity were simulated using a model of a porous

layer with a minute flow resistivity.

Ran Zhou (2010) [34] has studied the comparisons between the experimental

and predicted sound transmission loss values obtained from statistical energy

analysis are presented for two foam-filled honeycomb sandwich panels. The

accuracy of the prediction of the sound transmission loss using SEA greatly

depends on accurate estimates of: (1) the modal density, (2) the internal loss factor,

and (3) the coupling loss factor parameters of the structures. A theoretical

expression for the modal density of sandwich panels is developed from a sixth-order

governing equation. Measured modal density estimates of the two foam-filled

honeycomb sandwich panels are obtained by using a three-channel spectral method

with a spectral mass correction to allow for the mass loading of the impedance head.

The effect of mass loading of the accelerometer is corrected in the estimations of

both the total loss factor and radiation loss factor of the sandwich panels.

2.2. Material behaviour study of sound transmission:

In case of lightweight elements direct method was used to measure the

sound transmission and the magnitudes of inaccuracies involved in its use were

estimated. Testing was conducted on the anechoic chamber and the application of

the method to actual constructions was also tested.

There is a lack of published data on fibre reinforced ferrocement panels with

sound transmission class (STC) ratings. As part of consideration of Sound

transmission many materials like dry walls are attached to the structures to improve

their sound insulation. Measurements reported in the literature shows up to 100 Hz

or 125 Hz in case of ISO-140-3 (1995) [19]. Low frequency sound is equally

annoying and hence sound transmission loss at low frequency is also required.

Ferrocement panels are generally employed as internal partitions as well as

high performance walls separating internal to external environment. When properly

designed these partitions give reasonably good insulation (DIN4109-1989, [12].

7

Sometimes the sound reduction index gets affected by joints between the wall

structures.

Narang, (1992) [33] determined the acoustic performance of stud-framed

lightweight partition walls which are strongly affected by the presence or absence of

sound absorbing materials in the cavity. Fibreglass, a commonly used cavity

absorbent has come under criticism over potential health hazards owing to its

fibrous nature. Here some low cost alternatives that can be used for providing cavity

absorption in walls and offer sound insulation similar to fibreglass have been

studied. STC rating of 4 points was observed by using different cavity absorbents,

with options offering STC ratings similar to those achieved with conventional

fibreglass. The effect of adding an extra layer of plasterboard with a corresponding

equivalent sound reduction in the stud width was also studied.

The uses of rubber and plastic for sound insulation of party walls and floors

have been discussed by Craik, (1992) [7]. They are used as mainly in case of walls

and floors in buildings where in sound transmission takes place to a greater extent,

by using this material maximum amount of sound insulation is achieved. It was seen

that considerable reduction in weight of the building was achieved by the use of

resilient layers and these layers have to be designed carefully.

The number of components was relatively large as in the range of possible

designs. In either case the typical systems were to be identified and should be

included to determine the best method of modeling the coupling.

The consequence of lightweight buildings on sound transmission was

investigated by Craik, (1998) [8,9]. Changes in the building practice have led to an

increased use of lightweight components in modern buildings. Lightweight walls

and floors do not rely on mass to prevent sound transmission, which required the

knowledge of lightweight material used and the details of construction. Both

experimental and theoretical models are becoming important in the design of

lightweight buildings for sound transmission.

Sean Smith, (1997) [38] investigated the sound transmission through

lightweight parallel plates made of plasterboard and plasterboard combinations.

8

Double walls with plasterboard and line connected frame with chipboard and

plasterboard as parallel plates were studied using experiments and theoritical

approach such as SEA. Experiments were carried out to determine the sound

transmission into the double wall cavities and isolated cavities. Parametric surveys

were undertaken to analyse changes to the sound transmission through these

structures when the material or changes to the sound transmission through these

structures when the material or design parameter is altered.

Fringuellino and Sean Smith, (1999) [14] investigated the sound

transmission through hollow block walls. They investigated the characteristic

features of sound transmission through hollow walls. They used several different

types of wall of different thickness and materials and the sound reduction index of

the walls were recorded. The effects of additional plaster layers on the wall surface

were also discussed. The material properties of the block’s complex web structure

may strongly influence the sound reduction index at the low and high frequencies.

Kandaswamy (2003) [26, 27, ] has also investigated the sound transmission

through gypsum board panels, wood board panels, cavity ferrocement panels and

different type of walls and the sound reduction index, loss factor and transmission

loss are investigated.

Del Coz Díaz .J (2010) [11] investigated the most efficient numerical procedure

to predict the transmission loss (TL) through a multilayer wall for frequencies

ranging from 100 to 5000 Hz. The wall is made of lightweight concrete hollow

bricks joined by mortar, with gypsum lining on both faces. A set of tests using

source and receiving chambers have been modelled according to the basic

requirements of the ISO 140-1[18] standard rule and ISO 717-1[20] standard rule.

The convergence and accuracy of the proposed method are then assessed by

comparing FEM results with experimental measurements carried out by a certified

laboratory. Finally, the numerical procedures implemented in this work are used to

evaluate the acoustic behaviour for other structural building elements and reduce the

manufacturing time to develop new products in construction

9

2.3. Studies on using agricultural waste in building materials

Presently in India, about 960 million tonnes of agricultural waste is being

generated annually as by-products during industrial, mining, municipal, agricultural

and other processes. Of this 350 million tonnes are organic wastes from agricultural

sources; 290 million tonnes are inorganic waste of industrial and mining sectors and

4.5 million tonnes are hazardous in nature (Mannan et. al., 2001) [30]. Advances in

agricultural waste management resulted in alternative construction materials as a

substitute to traditional materials like bricks, blocks, tiles, aggregates, ceramics,

cement, lime, soil, timber and paint.

Researchers like Mannan, Daryl, Achyutha, Kurian have carried out in the

past used agriculture wastes such as saw dust ash, rice husk ash, palm-oil fuel ash

and bagasse ash as a replacement for cement. Natural fibres can be used in concrete

to produce particle boards, roofing sheets, and partition panels. Agricultural wastes

can also be used in non-load bearing concrete (Mannan et.al., 2001) [29] where

compressive strength is not important. Recently, an attempt has been made to use

Oil Palm Shell (OPS) as coarse aggregate in structural concrete (Mannan et.al.,

2001) [30]. In low-cost lightweight structures, agricultural waste as coarse

aggregate together with cement matrix can meet design specifications (Mannan

et.al., 2004) [31].

Although these researches are providing encouraging results, the lightweight

concrete mixes with coconut shell (CS) aggregate have not been investigated.

Concrete with CS as coarse aggregate can be used for the production of hollow-

blocks, ferrocement panels, and lightweight concrete and structural members of

low-cost houses. Hence, it is necessary to identify the potential use of coconut shell

for value added products.

3 OBJECTIVE AND SCOPE OF WORK

The principle objective of the work is to study the sound transmission

behavior of newer types of materials used in construction industry with respect to

acoustic insulation or transmission properties.

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The scope of work includes;

(i) The design and construction of a transmission loss suite to study the

transmission properties of building elements.

(ii) The study is limited to the experimental investigation of acoustical

transmission behavior and sound insulation properties of coconut shell

impregnated hollow blocks and reinforced ferrocement panels and panels

lined with wood wool boards and fibre reinforced panels.

(iii) The study is extended to the properties and effects of T L and cross

junctions.

(iv) To develop a software program using the principles of Statistical Energy

Analysis.

4 DESCRIPTION OF THE RESEARCH WORK

4.1. Experimental Investigation

(Design of Transmission Loss Suite and Experiments)

This chapter deals with the details of the design and construction of

transmission loss suite, measurement details in respect of materials studied, and

other instrumentation aspects involved. Other than the construction of transmission

suite, principal measurements made are sound reduction index of different

construction materials, longitudinal wavespeeds in different materials, and loss

factors associated with them.

4.2 Details of Transmission Loss Suite (TL Suite)

The plan and layout of the experimental set-up for sound transmission loss

suite designed and constructed for experimental investigations are shown in Fig

1(a). and 1(b). The dimensional details are indicated in figures. The TL

measurements were carried out by installing the specimens in the specimen frame of

normal size 0.94 x 0.64 m between the two reverberation rooms at the Acoustics

Section, National Physical Laboratory (NPL). Both the source room and receiving

room in the laboratory are irregular in shape with volumes of approximately 257 m3

and 271 m3 and are equipped with stationary diffusers. The floor of the receiver

11

room is vibration isolated to minimise the flanking transmission. Equipment

included a steady sound source of white noise was produced from noise generator

the noise signal was then fed in to and enhanced by a power amplifier and finally

emitted through a loudspeaker to produce a reverberant sound (diffused) field inside

the source room. Sound pressure levels inside the two rooms were sampled by

means of two sets of ½ inch calibrated microphones type 1220 each coupled with a

microphone pre-amplifier type 1201 and fed to a Norwegian Electronics type 830

dual channel real-time analyzer (RTA-830) for 1/3 octave band spectrum analysis. This

arrangement is shown in Fig. 2. A sand layer has been laid over the joists and the

flooring is laid over the sand Fig. 3.

The common opening between the source and receiver room is made up of two

independent wall elements with a 15 mm gap. An acoustic caulking is provided in

the gap, which minimise the transmission of acoustic energy from source to receiver

room. All the experimental specimens have been cast in-situ and are built to the size

of the common opening Fig. 4. The other walls of the source and receiver rooms are

230 mm thick.

4.3 Details of Instrumentation and Experiments

The important equipment used in this study are:

� Sound source [Omni-Directional Speaker System]

� Sound level meter ( Lactron – SL 4001)

� Level recorder and Vibration meter [PHOTON II signal with FFT

analyser]

� ½” inch microphone (DACTRON)

� Accelerometers (DACTRON)

The output of the microphone is connected to the analyser and recorded the

signal using analyser software in personal computer and has been used primarily for

reverberation time measurements. For vibration velocity measurement includes Tri-

axial (sensitivity 10 mV/g) and uni-axial accelerometers (sensitivity 100 mV/g) and

12

impact hammers with BNC connectors has been used which is connected to the

signal analyser which produces an acceleration of 10 m/s2 to an accuracy of ± 0.2

dB.

Fig. 1(a). Layout of experimental set-up for sound transmission loss

13

Fig. 1 (b). Measurement of Sound transmission loss, TL, in the laboratory

Fig. 2. Vibration isolation floorings with springs and steel sections

14

Fig. 3. Vibration isolation flooring filled with sand

Fig. 4. A typical view of the specimen being tested

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4.4 Maximum Achievable Sound Reduction Index of the TL Suite

In order to comply with ISO 140-1[18] the sound transmitted by any indirect

path as compared to the direct path should be negligible in the TL suite. For

measuring the maximum sound reduction index a test wall of 225 mm thick has

been constructed between the source and receiver room which is adequate for

lightweight structures. With the sound source switched on in the source room the

spatial average of spatial average of sound pressure levels is obtained. Similarly the

spatial average in the receiver room is obtained. Tables 1 and 2 give the background

noise levels and reverberation time of the TL suite. The sound reduction index is

then calculated as:

RW = L1 – L2 + 10 log (S/A) (1)

Where, S = area of the test specimen (m2)

A = Equivalent absorption in the receiver room

L1 = Spatial average of sound pressure level in the source room

L2 = Spatial average of sound pressure level in the receiver room

Table 1 Background noise levels of the transmission loss suite

Linear

(dB)

A-

weighted

dB(A)

Frequency (Hz)

31.5 63 125 250 500 1K 2K 4K 8K

43 25 35 33 41 28 26 23 24 22 22

Table 2 Reverberation time study of the transmission loss suite

Linear/ RT

(sec)

Frequency (Hz)/RT (sec)

125 250 500 1K 2K 4K 8K

1.9 1.9 1.7 1.6 1.4 1.2 1.1 1.2

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For measurement purposes the test signal has been filtered which is 1/3rd

octave wide which enables one to generate higher sound pressure levels in the

desired frequency band. In each frequency band of interest the sound pressure levels

generated should be at least 10 dB higher than the background noise levels in the

band. For repeatability a set of six complete measurements are taken, as a function

of frequency. They are paired into consecutive measurements without changing the

original order of the set. The difference in results between two members of every

pair is compared at all frequencies. If these values are exceeded at any one given

frequency all the values are rejected and the method of check is repeated. Identical

positions of measurements in the source and receiver rooms for measuring sound

pressure levels should be avoided for checking the repeatability. The sound

reduction index of the test specimen considering the transmission made from the

source to receiver room and vice versa is obtained. The velocity levels on all the

walls are also measured during the tests. The numbers of location points chosen for

measuring the sound pressure levels are five in the source and receiver room. Fig. 5

shows the maximum sound reduction index of the TL suite.

4.5 MEASUREMENT OF FLANKING TRANSMISSION

The flanking transmission is determined by measuring the average velocity

levels on the specimen and on the flanking surfaces in the receiver room. By

generating the sound field in the source room, the acceleration level has been

measured. From this the velocity levels have been obtained corresponding to seven

positions on the test wall. With the assumptions of radiation efficiency of unity,

(Schmitz, etal., 1999) [35, 36] which is valid above the critical frequency the sound

reduction index is calculated as:

R = Ls – Lv - 6.3 dB for f > fc (2)

Where, Ls is the sound pressure level in the source room, Lv is the velocity level on

the surface of the test element.

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The comparison of sound transmission calculated according to Eq. (2) in

comparison to the conventional method could detect the possible flanking

transmission. As Eq. (2) is valid only for frequencies above fc, differences should

only be examined above 2000 Hz. Therefore it is seen that the flanking transmission

is minimal for the transmission suite constructed.

4.6 EVALUATION OF SOUND REDUCTION INDEX

According to the standard ISO 140-3-1995 [19] the sound reduction index

for a partition in a building element is

RW = L1 – L2+10 log (S/A) (3)

This holds well under the assumption of diffuse sound fields.

Where, L1 = Mean sound pressure level in the transmitting room or source room

L2 = Mean sound pressure level in the receiving room

S = Area of the wall specimen

A = Absorption in the receiving room

Fig. 5. Maximum sound reduction index (Rmax) of the TL suite

0

10

20

30

40

50

60

100 160 250 400 630 1000 1600 2500 4000

Frequency (Hz)

So

un

d r

ed

ucti

on

in

dex (

dB

)

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By measuring the reverberation time T in the receiving room the absorption area in

the receiving room is

A = 0.163 (V /T) (4)

Fig.5. Shows the maximum sound reduction index of the TL suite.

4.7 MEASUREMENT OF LONGITUDINAL WAVE SPEED (CL)

The simplest way to excite a longitudinal wave on a structure is to strike it on

an edge with a plastic head hammer. Two accelerometers were mounted onto the

specimen at 2 m distance. (Fig.6) Each accelerometer is connected to a digital signal

FFT analyser. As a longitudinal wave is detected by the first and second

accelerometer, the analyser stores the respective pulses and the time interval

between the pulses is measured. Knowing the distance and time interval the

longitudinal velocity, cL is computed.

Fig. 3.11 Measurement of longitudinal wave speed

Fig.6. Measurement of longitudinal wave speed if the structure is alo

Fig.6. Measurement of longitudinal wave speed if the structure is along the edge

4.8 MEASUREMENT OF LOSS FACTOR (η)

In this investigation two types of loss factors are measured. One is the

internal loss factor and the other is the total loss factor. The internal loss factor is

Oscilloscope Charge Charge

Known distance

Plastic headed

hammer

FFT Analyser

19

the fraction of energy lost as heat in one radian cycle whereas the total loss factor is

the sum of the coupling and internal loss factor. Fig. 7 shows the experimental

arrangement for measuring the internal loss factor. The accelerometer is fixed to the

panel by using beeswax or anabond glue. The panel is excited from a plastic head

hammer and the vibration velocity output is detected and recorded. The signal from

the accelerometer is fed into conditioning amplifier and passed through tunable

band bass filter. The signal is further fed to the recorder, which records the

structural reverberation time decay. The loss factor (η) is evaluated as

60

2.2

Tf=η (5)

Fig.7. Measurement of structural damping

5 Experimental studies on transmission of sound through materials

and building components

5.1. Materials Details

The materials studied in the TL suite for sound transmissions are:

(i) Coconut shell impregnated Hollow blocks (120 mm, 170 mm, 220 mm)

FFT Analyser

Charge

Plastic headed

Measuring

amp

Test sample

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(ii) Coconut shell impregnated Hollow blocks (120 mm, 170 mm, 220 mm)

lined with absorbtive material

(iii) Coconut shell Hollow blocks (120 mm, 170 mm, 220 mm) double wall with

cavity thickness of (100 mm, 150 mm, 200 mm)

(iv) Coconut fibre impregnated Ferrocement lined with composite straw board

panels.

(v) Coconut fibre impregnated Ferrocement panels lined with wood wool

boards.

(vi) Coconut fibre impregnated Ferrocement panels lined with absorbtive

materials

(vii) Coconut fibre impregnated Ferrocement panels with cavity thickness of

(100 mm, 150 mm, 200 mm)

5.2. Test conditions:

1. Effect of plastering (10, 15, 20 mm)

2. Effect of cavity (100, 150 & 200 mm)

3. Effect of ties in ferrocement panels (8, 10 & 12 ties)

4. Effect of Junctions

In this study the coconut shell is been partially used by replacing with

aggregates used for construction. The coconut shell of similar age which is stored in

completely dried condition is used for the study. The crushing machine is designed

with sieves of 4.75, 2.36, 1.7 and 1.18 mm in order to get shell sizes similar to

aggregates used. Crushed coconut shell passing 4.75 mm and retained in 2.36 mm

sieve are used for this study. 50% of weight of the coarse aggregate has been

replaced with crushed coconut shells. The coconut shells are cured in water for 24

hrs in order to avoid the water absorption from the required water cement ratio. The

cured coconut shell is dried and external water is removed in atmospheric condition

before an hour for construction.

The required compressive strength of hollow block using is achieved at

1:1.25:1.02 weight ratio of cement, fine aggregate (sand), coarse aggregate and

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water cement ratio of 0.4, where 10% of weight of cement is replaced with fly ash

and 51% of weight of coarse aggregate ie, quarry dust is being replaced with

coconut shell. The hollow blocks with standard dimensions of 380 mm x 190 mm

with thickness of 150 mm, 170 mm and 220 mm are made. The study focuses on the

sound reduction index characteristics of coconut shell impregnated hollow blocks

made with coconut shell. The sound reduction index (SRI) has been measured for

twelve different wall surfaces.

Sound reduction index measurements have been made on the samples

constructed inside the transmission loss suite. In case of block walls, studies have

been made on the samples with and without plastered layers and with and without

cavity. Sound reduction index is calculated by taking the spatial average of the

sound pressure levels both in the source and receiver rooms.

Hollow blocks: Hollow blocks made of using coconut shell of three different

thicknesses have been studied. The test walls have been assembled and constructed

inside the transmission loss suite. Fig.8. gives the types of hollow blocks with the

airspace configurations, which is the important feature influencing the sound

transmission. For plastering, mortar thickness of 10 mm, 15 mm and 20 mm thick

was applied on either sides of the wall. Figs.13, 14, 15 shows the sound reduction

index (SRI) of the hollow blocks. The straight web geometry of the blocks is

resulting in higher sound insulation which is in conformity with other work (Scholl

and Weber, 1998 [37]; Fischer et al, 1998 [13]).

Ferrocement Panels: Fibre impregnated ferrocement panels made of using

coconut shell are tested. The panels are cast in-situ and erected for experimentation.

The material by itself has a better performance than the conventional brickwork and

concrete of high flexural strength and modulus of elasticity. The panel consists of

two layers of chicken mesh of 22 gauge thick with hexagonal opening wound over

on the top of one layer of weld mesh of 10 mm x 10 mm opening (10 gauge thick).

Cement mortar of 1:2 ratios has been used in casting the specimens. The sizes of the

panels cast for testing are 3 mm x 2.1 mm x 20 mm thick. Ferrocement panels with

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different structural systems have been studied for sound transmission. Systems of

ferrocement panels studied are as follows:

� Single fibre impregnated ferrocement panel.

� Fibre impregnated Panel with cavity

� Fibre impregnated Panel with cavity insulation. High density fibre

glass wool of 50 mm thick (48 kg/m3)

Fig.13 shows the measured sound reduction index of the Fibre impregnated

ferrocement. Fig.14 Shows the loss factor measurements on the panel. Fig.15 shows

the sound reduction index of the cavity ferrocemnt panel. Figs. 16, 17, 18 shows the

sound reduction index of the panel with cavity of 100 mm, 150 mm and 200 mm

respectively. Fig. 19 shows the loss factor measurements of the panel with cavity.

All dimensions are in cm

Fig. 8. Types of hollow blocks studied

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5.3. Theoretical prediction model using SEA

The theoretical computations have been computed by developing software

through Statistical Energy Analysis approach. The Programme is written in Visual

Basic. Statistical Energy Analysis permits calculation of energy flow between

connected resonant structures such as plates, beams and reverberant sound fields in

an enclosure. The term statistical refers that averages are involved and randomness

is assumed in excitation, the distribution of resonance frequencies and matching

condition and principles are employed considering the coupled systems. The model

showing the power flow between the subsystems is shown in Fig.9. [6]. The flow

chart for the SEA model is shown in Fig.10 (a, b).

Fig. 9. SEA model for three subsystems

Measured and predicted results correlate well and the difference is just 2-3

dB between the measured and predicted values. Figs. 13, 15 and 18 shows the

predicted and measured sound reduction index also. The methodology and the

software provide the advantage of selecting the materials for desired sound

transmission loss in a user friendly way. [1]

Room 1

Plate 2

Room 3

W1

W12 (η12) W23 (η23)

W21 (η21) W32 (η32)

W13 (η13)

24

Flow chart

Fig.10(a). Flow chart of SEA model

25

Fig.10 (b). Flow chart of SEA model

26

5.4. Real time simulation results using ODEON

The calculation of transmission through walls including auralization in

receiving room is done using the room acoustic simulation software Odeon version

9. The room acoustic simulation software Odeon is based on ray tracing in

combination with a secondary source radiation method for reflections after a certain

transition order, typically 0 – 3 order of reflection [22, 23, 24]. In the Odeon model

the particles are treated as carries of sound energy that is reduced after each

reflection with the frequency dependent reflection coefficients of the surfaces.

In the following tests the decay curves and integrated squared impulse

responses have been investigated at the 1 kHz octave band in the source room as

well as in the receiver room. The source room with dimensions 8.3m X 2.3m X 2.5

m and receiver room with dimensions 5.4 m X 3.6 m X 2.5 m and the transmitting

surface of 63 m2 is modeled as in the experimental model as shown in Fig.11. The

white noise is produced for auralization in the model. The receiver and source

position are placed as per ISO 140-3-1995 [19] and recorded results are analyzed.

Hence the real time simulation is carried on using Odeon software and the results

are compared with experimental results and theoretical results.

Fig. 11. 3D model created Using ODEON for real time analysis

27

6. Results and Discussions

The sound insulation characteristics of fibre impregnated hollow block

depend on block design structure of the webs and holes. In study a constant web

thickness and holes are considered with varying thickness of block. Fig.12 shows

the sound reduction index for 120, 170 and 220 mm respectively. The sound

reduction index (SRI) for all the three thickness of the fibre impregnated hollow

block wall has a broader dip between 50 Hz to 250 Hz. At higher frequencies; there

is another dip at 1250 Hz, which is not very predominant for 170 and 220 mm. The

dip is attributed due to the coincident frequency associated with the thin surface

layers of fibres and the coconut shell which is used in hollow blocks. The SRI of

fibre impregnated hollow blocks exhibits 38, 40 and 43 dB at 500 Hz for 120, 170

and 220 mm respectively.

As expected when the total wall thickness decreases the critical frequency

increases and the overall sound insulation decreases. Similar dips appear at the

higher frequencies due to the thin surface layer of fibre impregnated hollow block.

All the three types of fibre impregnated hollow are made from the same

manufacture using same material and mixing ratios. Straight webs inside the fibre

impregnated hollow block provide higher bending stiffness.

Two important mechanisms for the fibre impregnated hollow block walls is

that the block undergoes pure bending and hence the bending wavespeed increases

with frequency due to the effect of fibres. The density and the curves in coconut

fibre decreases the intensity flow of longitudinal and bending waves which

increases the transmission loss factor of the hollow block and as well as the

ferrocement panels. The limit of regarding the block when the bending wavelength

is six times the plate thickness, given by f = cL/20h for homogenous plates.

Generally the bending wave speed is slightly lower than transverse wave speed [2]

where the difference is related by the poisson ratio.

Other important parameters include, total loss factor (TLF), the longitudinal

wavespeed of the panel and the acceleration level difference on either side of the

wall for an airborne source. The total damping (TLF) of the wall was calculated

28

using the measured standard decay rate of the wall, where the source was an

acoustic hammer, an average of 6 positions was recorded [1].

Plaster layers are applied to walls to seal the face of the blocks. This can

increase the total mass of the wall and also increases the air flow resistance leading

to improved sound insulation properties. In order to study the effect of plaster layers

on sound insulation of hollow block walls, plaster thickness of 5, 10 and 15 mm has

been applied on all the blocks.

Figs.13, 14 and 15 shows the sound reduction index of the fibre impregnated

hollow blocks of 120, 170 and 220 mm with plaster layers of 5, 10 and 15 mm

respectively. The curve shows dip at low frequency range of 125-250 Hz. At high

frequency of 3150 Hz there is another dip occurring which can be attributed due to

the critical frequency.

From Fig.16, It is seen that the sound reduction index of the fibre

impregnated panel with cavity shows prominent dips at low frequency at 75 Hz

which are due to the cavity resonance. This in turn matches well with the predicted

cavity resonance values which were around 75 Hz. At high frequency regions

coincidence dips predominate at 1500 Hz which again coincides with the predicted

value. Critical frequency value of the fibre reinforced ferrocement panel behaves

like a thin plate. The measured results all tend to level off at very high frequency

due to other transmission paths.

In case of cavity with absorptive material the sound reduction index

gradually increases due to the presence of material inside the cavity thereby

increasing the coupling of the cavity with the material. From Fig.17 it is seen that

the dips are more predominant at high frequency regions at 1250 Hz, is due to the

first cross cavity resonance of the air. This value coincides with the predicted

frequency value of around 1250 Hz from Fig.18. The agreement between the

measured and predicted results improves as the material has been added to the

panel. Fig.19. shows the measured loss factor of coconut fibre reinforced

ferrocement panel. It is clearly seen that the total loss factor of the panel with

29

absorptive material shows higher loss factor than the cavity fibre reinforced

ferrocement panel.

The results are then compared with the theoretical investigation using SEA

approach. Fig.16 and Fig.17 shows the experimental value coincides with the

predicted frequency value of around 1250 Hz. The agreement between the measured

and predicted results improves as the material has been added to the panel.

Fig.12: Measured Sound Reduction Index (SRI) of hollow blocks

Fig. 13: Measured Sound Reduction Index (SRI) of 120 mm hollow block with

plastering.

30

Fig. 14: Measured Sound Reduction Index (SRI) of 170 mm hollow block with

plastering

Fig. 15: Measured Sound Reduction Index (SRI) of 220 mm hollow block with

plastering

31

Fig. 16: Measured sound reduction index of ferrocement panel 20 mm thick (♦) and

fibre reinforced ferrocement panel of 20 mm thick (■).

Fig. 17: Measured sound reduction index of ferrocement panel with cavity of 50 mm (�),

100 mm ( ), 200 mm, (◊) with experimental values (-------) and predicted values using

SEA (--------).

32

Fig.18. Measured sound reduction index of coconut fibre reinforced ferrocement panel

with cavity and absorptive material 50 mm (∆), 100 mm (□), 200 mm (◊), with

experimental values (───) and predicted values using SEA (---------).

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

31.5 5

080

125

200

315

500

800

1250

2000

3150

5000

Fequency (Hz)

Loss facto

r (T

LF)

Fig.19: Measured loss factor of ferrocement panel (◊) and with absorptive material (□)

33

7. Conclusion

A study on sound transmission performance characteristics of coconut shell

hollow blocks, Coconut fibre impregnated ferrocement panels and other building

systems has been carried out in this work. From the studies conduct in this suite it

has been observed that the coconut shell hollow blocks of 120, 170, 220 mm thick

exhibit a sound reduction index of 38, 40, 43 dB respectively at 500 Hz. Which is 6

dB higher than normal hollow blocks. There is a considerable difference of SRI of

the blocks with and without plastering. The difference is order of 7-8 dB depending

on the thickness of the block. A comprehensive experimental study on Coconut

fibre impregnated ferrocement panels for sound transmission performance has been

investigated. The SRI of the panels (20 mm thick) is 30 dB whereas for cavity panel

it increased by 5 dB. Fibre reinforced ferrocement panel with 50 mm cavity and

double triangle ties exhibits 40, 35, 33 dB of sound reduction index at 500 Hz with

two, four and eight ties respectively. As the numbers of ties are increased from 2, 4,

8 the sound reduction index value decreases at high frequency. This is because of

the fact that greater transfer of energy occurs due to the presence of ties. But there is

a good increase at 125 Hz with maximum number of ties. Theoretical predictions

and comparisons using Statistical Energy Analysis approach has been done and

experimental results agree well. The difference is of the order of 2 – 4 dB between

experimental and theoretical values. From the investigation it is seen that the using

natural coconut fibres in building components like hollow blocks and fibre

reinforced ferrocement panels can be explored as noise insulating elements.

34

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38

Visible Research Output:

LIST OF PUBLICATIONS

1. Mahavir Singh, Omkar Sharma and Dharm Pal Singh, “Some Physical

Parameters Affecting Sound Transmission Loss” Proc. of National Symposium

On Acoustics (NSA 2008), Visakhapatnam, PP. 353 - 358, Dec. 2008.

2. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Reduction of Sound

Transmission through Lightweight Gypsum Board Walls,” Proc. of 7th

International Conference on Advances in Metrology (AdMet – 2009), New

Delhi. PP. 120 – 122 Feb 2009.

3. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Reducing Noise in

Your Apartment,” Proc. of 7th International Conference on Advances in

Metrology (Ad Met – 2009), New Delhi. PP. 123 – 125. Feb 2009.

4. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Sound Transmission

through Single and double Leaf Partitions.” Journal of the acoustical Society of

India, 36(2), pp. 96 -101, Apr. 2009.

5. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Sound Transmission

through Lightweight Concrete Walls” Proc. of 16th International Congress on

Sound and Vibration (ICSV16), Krakow, pp. 1 – 10, Jul. 2009.

6. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Sound Transmission

through Both Lightweight and Masonry Single and Double Leaf walls,” Proc.

of 2nd

National Conference on Innovations in Indian Science Engineering &

Technology (NCISET 2009), New Delhi, pp. 1 – 7, Jul. 2009.

7. Mahavir Singh, Omkar Sharma and Dharm Pal Singh, “Sound Transmission

Loss of Lightweight Walls,” Proc. of 10th

Western Pacific Acoustics

Conference (WESPAC X), Beijing, PP. 1-10, Sep. 2009.

39

8. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Sound Transmission

through Lightweight Partitions,” Proc. of ACOUSTICS High Tatras 2009 “34th

International Acoustical Conference - EAA Symposium,” Slovakia, pp.1-10,

Sep. 2009.

9. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Sound Transmission

through Wall Elements,” Proc. of National Symposium on Acoustics

(NSA2009), Hyderabad, pp. 1-6, Nov. 2009.

10. M.Singh, D.P.Singh, and O.Sharma, “Airborne Sound transmission in

lightweight wall design structures for residential and commercial buildings,”

Accepted in Proc. of the 20th International Congress on Acoustics (ICA-2010)

Sydney, pp. 1-6, Aug. 2010.

11. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Vibration in

Dwelling Units from Road Traffic” Proc. of National Symposium On Acoustics

(NSA 2010), Govt. PG College Rishikesh, pp. 66-72, Nov. 2010.

12. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Controlling

Reverberant Noise in Rooms using Sound Absorptive Materials” Proc. of

National Symposium on Acoustics (NSA 2010), Govt. PG college Rishikesh,

pp. 73-78, Nov. 2010.

13. Mahavir Singh, Omkar Sharma and Dharm Pal Singh, “Room Acoustics –

Design for Internal Acoustic Quality,” Journal of the Acoustical Society of

India, 38(1), pp. 3-10, Jan. 2011.

14. Mahavir Singh, Dharm Pal Singh and Omkar Sharma, “Sound Transmission

through Building Elements,” Proc. of Indo-US Workshop on Nanosonic &

Ultrasound (IUWONU2011) and International Conference on Nanotechnology

& Ultrasound (ICNU2011), Trichy, pp-52-70, Jan.2011.

15. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Experimental

Investigations of the Sound Transmission Loss of Window Panels” Proc. of 1st

National Conference on Advances in Metrology (AdMet-2011), Banglore, pp.

1-6, Feb. 2011.

40

16. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Acoustic Comfort –

Noise Control for Buildings” New Dimensions of Physics of Proc. of National

Conference on Ultrasonics (NCU-2011), Jhansi, pp. 1-14, Mar. 2011.

17. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Sound Transmission

through Cavity Walls Constructed from Gypsum Board,” GESTS Int’l Trans.

Acoustics Science and Engr., 15(3), pp. 107-112, Mar. 2011.

18. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Experimental

Analysis of the Sound Transmission Loss of Single, Double and Triple Glazing

Window for Traffic Noise Reduction, Journal of the Acoustical Society of

India, 38(3), pp. 106-113, July. 2011.

19. Mahavir Singh, Dharam Pal Singh and Omkar Sharma, “Sound Insulation

Performance of Double-leaf Structure,” Acoustic Waves of Proc. of National

Symposium on Acoustics (NSA 2011), Bundelkhand University Jhansi, pp. 15-

24, Nov. 2011 (Received a Best Paper Award).

20. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Sound Transmission

Loss of a New Designed Lightweight Partition,” Acoustic Waves of Proc. of

National Symposium on Acoustics (NSA-2011), Bundelkhand University

Jhansi, pp. 62-77, Nov. 2011.

21. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Vibration in

Residential Environments due to Road Transporation,” Journal of the Sound

Vibration and Hardness, (in Press).

22. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Experimental and

Theoretical Evaluation of Sound Transmission through Double Window

Panels,” GESTS Int’l Trans. Acoustics Science and Engr. (in Press).

23. Mahavir Singh, Omkar Sharma and Dharam Pal Singh, “Some Practical

Aspects of Absorption Measurements in Reverberation Room,” GESTS Int’l

Trans. Acoustics Science and Engr. (in Press).

24. Mahavir Singh, Omkar Sharma, Dharam Pal Singh and R.S.Upadhayay,

“Theoretical and Experimental Investigation for Sound Transmission through

41

Multi-layered Window Structures,” 2nd

National Conference on Advances in

Metrology (AdMet-2012), ARAI Pune, pp. 1-7, Feb. 2012.

25. Dharam Pal Singh, Mahavir Singh and R.S. Upadhayay, “Acoustic Properties

of Coconut Coir Fiber Sound Absorption Material,” Proc. of National Seminar

on Materials Characterization by Ultrasonic,(NSMCU), New Delhi, pp. 1-7,

Apr. 2012. (Received a Best Paper Award).