Universiti Malaysia Sarawak

I

DESIGN OF SUBWOOFER AMPLIFIER

AIDAWATI BTE MUSTAPHA

Universiti Malaysia Sarawak

1998

TK

6565 A55

A288

Dorana Penyerahan Tesis Universiti Malaysia Sarawak

R13a

DORANG PENYERAHAN TESIS

Judul: DESIGN OF A SUBWOOFER AMPLIFIER

SESI PENGAJIAN: 1998/1999

Saya AIDAWATI BTE MUSTAPHA

(HURUF BESAR)

mengaku membenarkan tesis ini disimpan di Pusat Khidmat Maklwnat Akademik, Universiti Malaysia Sarawak dengan syarat-syarat kegunaan seperti be:ribt:

1. Hakmilik. k.ertas projek adaIah di bawah nama penulis melainkan penulisan sebagai projek. bersama dan dibiayai oleh UNIMAS, hakmiliknya adalah kepunyaan UNIMAS.

2. Naskhah salinan di dalam bentuk kertas atau mikro hanya boleh diboat dengan kebenaran bertulis

daripada penulis.

3. Pusat Khidmat Maldwnat Akademik, UNIMAS dibenarkan membuat salinan Wltuk pengajian mereu.

4. Kertas projek. hanya boleh di1eIbitkan dengan kebenaran penulis. Bayaran royalti adalah mengikut kadar yang diperserujui kelak.

5. • Saya ~tidakmembenarkan Perpustakaan membuat salinan kertas projek ini sebagai bahan pertukaran di antara institusi pengajian tinggi.

I 6. •• Sila tandakan ( .t )

[:=JSULIT (Mengandungi maklumat yang berdarjah kese1amatan stau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMlI972).

c:=:J

TERHAD (MengandWlgi maklwnat TERHAD yang telah ditentukan oleh organisasil

badan di mana penyelidikan dija1ankan). ~ TIDAK. TERHAD

Disahkan oleh

(TANDATANGAN PENULIS)

.'

(TANDAT ANGAN PENYELIA)

Alamat tetap: NO 300A LORONG 6A1

TAMAN MATANGJAYA EN. NG LIANG YEW

Nama Penyelia 93050 JALAN MATANG. KUCHING

Tarikh: 12 HB OKTOBER, 1998 Tarikh: 12 HB OKTOBER, 1998

CATATAN * Potoq YIIIII ttdak berlreaaan.

** Jika KeJ1u ProJek Ini SULIT atau TERRAD, .... hunpirkan nrat daripluIa pihak berk1lasal

orpabasl berIre_ denpn menyertakan sekaU telDpoh krl1as proJek. Ini perlu dJkeIasl!.l sebapl SULIT atau TERHAD.

Tesis ini telah dibaca dan disahkan oleh :

• • • • • • • •• • 0 ' • • •• • • • 0 . ' 0 ' • •• • 0 • • •• • • • • • •

Tarikh (Mr. Ng Liang Yew)

P~~~~~~1T7~ALMakium

a

t

Akademik AYSIA SARAWAK

DESIGN OF SUBWOOFER AMPLIFIER

AIDAWATI BTE MUSTAPHA

Tesis Dikemukakan Kepada

Fakulti Kejuruteraan, Universiti Malaysia Sarawak Sebagai Memenuhi Sebahagian daripada Syarat

Penganugerahan Sarjana Muda Kejuruteraan

Dengan Kepujian (Kejuruteraan Elektronik dan Telekomunikasi) 1998

Dedications

This thesis is dedicated with deepest love and affection to my beloved parent, Mustapha Bill Melek and Hadrah Bte Hj. Le1lltlll, brother andsister. Their love, patience, guidance, wisdom and strenght have inspired me throughout the three anda halfyears in

University Malaysia Sarawak to be the best that I can be

Acknowledgement

Firstly, the author would like to express his grateful to Allah Almighty, only with

His

guidance the author can complete this project.

The author would like to express his deepest thanks to all the people who had given their support to make this project. The author's greatest appreciation to the project supervisor : Mr. Ng Liang Yew for his worthy suggestions and invaluable knowledge shared with the author during this project guidance.

Lastly, the author wishes to convey his sincere gratefulness to his family members and friends for their support and endless encouragement.

J iii

Abstract

Nowadays'subwoofer amplifier' has a potential to expand. It is a support system to audio video system especially in the using of multimedia. The audio system which is always used in the multimedia could not give a dramatic effect such as bomb explosion

and earthquake. To have this effect the designed will concentrate only to amplifier

vibration effect while sound effect is neglected. The sound effect can be found from other

audio amplifier system which will be used together with subwoofer amplifier.

The basic design is divided into three parts as to achieve the desired goal. There are as below ;

I. filter

u. amplifier

III. supply voltage

Active components which mostly used in this project are semiconductor in the form of operational amplifier and integrated circuit. Other semiconductor component used is

transistor. The use of operational ~plifier and integrated circuit have eased the project

carried out because it only required simple external connection.

Abstrak

'Subwoofer Amplifier' mempunyai potensi untuk berkembang pada masa kini.

Ianya merupakan sistem sokongan kepada sistem audio video terutamanya dalam

penggunaan multimedia. Biasanya sistem audio yang terdapat dalam multimedia tidak

dapat memberi kesan yang dramatik untuk sesetengah keadaan seperti apabila born meletup ataupun gempa bumi berlaku. Penggunaan sistem subwoofer dijangka dapat membantu menambahkan kesan dramatik ini. Bagi mendapatkan kesan ini penguat yang

direka hanya menitikberatkan kesan gegaran manakala kesan bunyi tidak diperlukan.

Kesan bunyi boleh didapati oleh sistem penguat audio lain yang akan digunakan

bersama-sama dengan sistem subwoofer ini.

Bagi mencapai matlamat diatas keperluan asas rekabentuk adalah terbahagi kepada tiga bahagian utama iaitu :

i) bahagian penapis

ii) bahagian penguat

iii) bahagian voltan bekalan

Kebanyakan komponen aktif yangi-isunakan dalam projek ini adalah separa pengalir dalam bentuk penguat kendali dan Iitar bersepadu. Bahan separa pengalir lain yang digunakan adalah transistor. Penggunaan penguat kendali dan litar bersepadu memudahkan projek ini dijalankan kerana ia memerlukan sambungan luaran yang mudah.

Pusat Khidmat Makiumat Akademik

VNIVERSITI MALAYSIA SARAWAK

TABLE OF CONTENTS Pages Title page ii Dedication Acknowledgement 111 iv Abstract Abstrak v Vl Tables of Contents List of Figures Vll Xl List of Tables

List of Symbols and Abbreviations X111

Chapter 1 : Introduction 1.1 Introduction

..

:,. 1 1 1.2 Objective 2 1.3 Project Overview 3 1.4 Outline of thesis vi

Chapter 2 : Active Filter Design

2

.

1

Active filter 4

2

.

2

Basic active filter design 4

2

.

3

Low pass filter design

7

2.4

Gain and phase shift of the circuit 10

2

.

5

The VCVS high pass filter 11

2

.

6

Fourth order high pass filter 13

2.6.1

First stage design

15

2.6

.

2

Second stage design

16

2

.

7

Fourth Order low pass filter design

19

2.7.1

First stage low pass filter design

19

2

.

7

.

2

Second stage low pass filter design

20

2

.

8

Complete band pass filter design

23

Chapter 3 : Power amplifier

3.1

Power amplifier

25

3

.

2

Power bridging

26

3

.

3

Power amplifier desiJa,

28

3

.

3

.

1

The inverting amplifier

30

3

.

3

.

2

Non inverting amplifier

31

Chapter 4 : Power supply

4.1 Introduction of power supply 4.2 Constant voltage supplies 4.3 Basic stabilizing circuit 4.4 Load regulation

4.5 Voltage regulator 4.5.1 Load effect

4.5.2 Dual transformer power supply 4.5.3 Design ±12V power supply 4.5.4 Design ±15V 4.6A power supply 4.6 Component selection

Chapter 5 : Circuit Implementation and testing 5.1 Design requirement

5.2 Matching input and output signal 5.3 Transistor heat sinking

Chapter 6 : Suggestion Chapter 7: .Conclusion References 36 36 37 38 41 42 43 43 44 44 52 53 58 63 64 66 viii

l

II

r

Figure la Figure 2a Figure 2b Figure 2c Figure 2d Figure 2e Figure 2f Figure 3a Figure 3b Figure 3c Figure 3d Figure 3e Figure 4a Figure 4b Figure 4c Figure4d Figure 4e Figure 4f Figure 4g UST OF FIGURES

Title of Figures Pages

Overviews of musical processing signal 2

Sallen Key Second order filter 5

Redrawn circuit for dc condition 9

Circuit diagram for high pass filter 11

Cascading filter to obtain higher order filter 14

Schematic diagram for the band pass filter 22

Frequency response of the band pass filter 24

The signals involved in parallel bridging 27

Inverting amplifier 29

Non inverting amplifier 30

Schematic diagram of the amplifier 34

Mounting power op amp module at the chassis as heat

sinking 35

Response characteristics of power supply 37

Line regulation in ~relationship between Vin and V out 40

How regulators fit into power supply scheme 41

Schematic diagram of the voltage supply 46

DC pulse waveform of rectifier 47

Output voltage from filtering capacitor 48

Dual supply with dual transformer 51

ix

Figure 5a Instrument set up for evaluation of amplifier 54 Figure 5b Testing the filter with a music signal with the volume

control is set to maximum 54

Figure 5c Square wave test 55

Figure 5d Output from the power amplifiers 56

Figure 5e Maximum swing of music signal 57

Figure 5f Mounting the transistor on the heat sink 62

.'

LIST OF TABLES

Title of tables Page

Table Sa

Table 5b

Junction to ambient thermal resistance's

Thermal resistance between the transistor case and heat sink.

59

60

/ VI Vo V Av Is Ircp I Opamp

UST OF SYMBOL AND ABBREVIAnONS

input voltage output volatge voltage voltage gain surge current repetitive current current operational amplifier xiii

CHAPTER 1 INTRODUCTION

1.1 IDtroductioa

Subwoofer Amplifier is an amplifier which amplify subsonic frequency. Subsonic frequency also known as infra bass frequency and no sound generated at this frequency. But we can feel the vibration from this kind of frequency. An

amplifier should be used to generate enough vibration which can fell by the user. The subwoofer amplifier will be combine with other audio systems. It mainly being used as a part of multimedia system. The realistic sound system combined with a subwoofer system will greatly enhance the overall performance of the multimedia system.

1.2 Objective

Objective of this project is to design and built an amplifier which can produce vibrations that cannot be heard. The sound effect will be reduced as much

'tt~,

as possible. The working frequencies choosed in this project are 5Hz to 40Hz, a very low frequency range. This frequency range is chosen because we do not want any dc components which affect the quality of vibration. A frequency higher than 40Hz will be and this will not fulfill system requirements.

,

_{An amplifier have 60 watts output power are decided to be built to move}

the speaker. The speaker which is suitable to be used must have a large cone because only this kind of speaker can capture very low frequency. To move the large cone speaker, the power amplifier must have a high output power. If the output power is low maybe is no vibration we can feel.

1.3 Project overview

The subwoofer amplifier have two essential parts assigned in sound processing. The first part is the filter and another part is power amplifier. The figure below describe how the signal process take place.

High power Subsonic signal

M.USiC signal

"'1

_Power

.->---I....

~- Active Filter

•

I

Amplifier

Figure la : Overview of music processing signal

All the active component which have been used in this project are op amp, integrated circuits and transistors. The usage of op amps and integrated circuits cam

simplify the circuits design and also they can reduce the cost of this project.

1.4 Outline of thesis

Chapter 1 gives the overview of this project including introduction, objective, project structure and outline thesis.

Chapter 2 presents the theory and application to design active filter by using 741 operational amplifier (op amp). The practical result also include in this chapter.

Chapter 3 presents the theory and applications to design power amplifier by using L465 operational power amplifier.

Chapter 4 concentrates on power supply to both filter and power amplifier.

Chapter 5 brief about matching overall design, testing and calculation of the result achieved from the test.

Chapter 6 is conclusion of the project. It also gives some suggestion and recommendations for this ~~ject for future enhancement.

Pusal Khidmat Maklumat Akademik

UNIVERSITI MALAYStA SARAWAK /

CHAPTER 2

ACTIVE FILTER DESIGN

2.1 Active fdter

Since subwoofer amplifier need a frequency range between 5Hz to 40Hz, it is necessary to make a filter which operates at that frequency. At that frequency range the frequency lower than 5Hz and higher than 40Hz will be attenuated. This frequency range is enough to fulfill the needs of subwoofer amplifier design which means remove the sound from the amplifier.

The type of active filter have been designed In butterworth filter. Butterworth filter is expected to be suitable to fit in this application because of it's flat response in the pass band region. Fourth order filter is choose because this order have rapid attenuation in roll off region. This action will keep more desired frequency and removed unwanted frequency.

2.2 Basic active fdter design

..

'

,

The most popular active filter is using voltage control voltage source (VCVS) method. This type of circuits was first proposed by Sail en and Key and it is relatively

easy to design and implement. Figure 2a illustrates about SaIlen key second order filter. It

employs the infinite gain VCVS concepts associated with the operational amplifier and

L'

I'

t

the

circuits offers external gain adjustment via components Ys and Y6. This type of filter

structure, employing the non-inverting (positive gain) operational amplifier, exhibits a high Q-factor sensitivity, the circuits, gain [K = 1 +

RdRsl

Because of this sensitivity, the configuration is restricted to low Q and low gain values with a trade off being a wide frequency bandwidth.

Y4

I

I

I

I

b C

...

~

Y2 Y.

_I

q

l

~

_i

~~ Y6

l

Vo

rt~ 'is

Figure 2a : Sallen Key second order filter

A is assumed very large which implies that Vb = Vc

Writing the nodal equations at node (a), (b) and (c) giving Node (a) :

5

Node (b)

v"f! + (V" - VcJY1 = 0

Node (C)

From which (we get)

Y.

V

= 6

V

C y.+y. 0

5 6

substituting this into equation (2.6) yields

from which (2.2) (2.3) (2.4) (2.5) (2.6) (2.7) that is (2.8)

Equating equations (2.5) and ( 2.8) yields

6

Filially ;lIter same manipulation. we obtain the expression

v

o

(2.9)

2.3 Low Pass Filter Design

Here

I

Y = ­

I R '

I

from the I!quation (2 .9)

manipulation of the expression yields

'tl~

Now K = I + R4!R3 which is the de gain of the stage and the expression may finally

be written as

t

if we note further that W 2

=

I then we may compare equation o C)C₂ R)R3

(2.1 0) with the standard fonn for a second-order low pass filter

(2.11)

Where COo is the 3 dB frequency for the Butterwoth case and bocoo is the frequency at the end of the ripple band for the Chebyshev filter. The coefficients bo ,

bo , etc. are the appropriate coefficients for the prescribed filter response.

Comparison between equation (2.10) and (2.11) yields

(2.12)

We must now introduce normalization into the components and design

parameters in order to produced a rationalized design procedure. Let co0

2

= 1 radls,

C,= C2 = I farad. Then the equation (2.12) becomes

.~, I bo _{= R)R2} (2.13) 1 1 b - - +- (2-K) 1 - R, R2

Now we know that there are six unknowns and therefor a certain degree of

component selectivity will have to be made since a unique solution is not possible.

From equation (2.13) we obtain

(2- K) hi = b"R2 + R

2

which may be written as

and which has a solution

(2.14)

So far we have nonnalized the capacitor C1 , C2 and obtained the nonnalized

values for the resistors R\ , R2, we now have to obtain values for the gain resistors R3

, It, for the good circuit design condition of minimum dc offset.

Figure 2b shows the redrawn circuit for the dc condition where the capacitors are now represented by open circuits

For minimum dc offset, V+

=

V_ or

hence

Figure 2b: Redrawn circuit fol' d.c condition