أصدرت دار جامعة عدن للطباعة والنشر سلسلة الكتاب الجامعي 8-2017 بعنوان Fundamentals Of Noise Control
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Preface
Noise is unwanted sound. The word noise in this book is used to mean the common unwanted sounds such as traffic and noise produced in factories by machines and other activities, etc. Noise is undesirable because it causes distraction by interfering with the mental activities and speech. It also masks the satisfactory hearing of speech and music. Sustained exposure to high-level noise has dangerous effects on physical and mental conditions of an individual. It results in fatigue, inefficiency, deafness or even nervous breakdown. A noise level of 130 db may be sufficient to rupture human eardrums.
Noise is a complex conglomeration of routine environmental and industrial operation. For noise insulation design one may restrict to either environmental noise or industrial noise alone depending upon the situation. In environmental noise, one has to take into account the noise from radios, blaring loud speakers, traffic and the indoor noise such as running water taps, fans, banging of door and window shutters, dragging furniture, etc. The factory noise from lathes, planning machines, drilling machines, forge hammers, running trolleys, exhausts, etc. comprises the industrial noise.
It is the business of the design engineer or architect to see that he designs a building, a workshop or workstation for less noise and better hearing. The talk of less noise and better hearing is similar to conditioning the building with respect to sound. Sound conditioning of a building is as important as air-conditioning for human comfort. Noise and sound can be differentiated in the same way as we differentiate between a friend and an enemy. Physically both are same, and therefore can be studied under a common group. But the ways to deal with them must differ characteristically. Whatever noise or sound may mean to a scientist, it is only a problem of vibrations. It is not only the design engineer, who is concerned about noise control; the scientist who wants to make precise measurements is equally concerned about the interference of noise or any minor vibration that may creep into his cell and disturb his delicate experimental set-up.
Faculty of Engineering, University of Aden, has academic regulations to update its plan of studies and curriculums in the various departments every 5 years to include the advancement in technologies and engineering fields into the curriculums and to prepare the study plans, their contents and undergraduates students to be able to work in the engineering and industrial sectors efficiently. The idea of preparing the materials of this book came in the year 2003, when the Faculty of Engineering introduced in the Mechanical Engineering Department three options; namely: Applied Mechanics, Thermal Engineering and Production & Industrial Engineering. Goals of these developments in the Mechanical Engineering Department were to undergo into the process of preparing graduates, who are scientifically oriented in the above fields of specialisations to enable them tackling engineering problems in a better and offering better understanding of the problems.
In order to design suitable and world-wide competent option in Applied Mechanics, references have been made to various universities and institutes for selecting suitable subjects for this option. One of these subjects was Noise Control to be given as an elective subject to the final year students in Applied Mechanics. In order to put the suitable chapters and knowledge into this subject, we made visits to various industrial and power generation sectors inside and around Aden Governorate. We tried to discuss the noise problems with concerned parties to know their problems and technical requirements to solve noise problems not only in the industry, but also in our society. We found that most of the administrations, engineers, trade union members and leaders have absolutely no idea about the noise effects on machines, workers’ health and working environment as well as about ISO Standard and OSHA regulations that organise the working hours under high noise levels to avoid exposure of workers to hearing damage and other health impairment. This put us into a new challenge. Therefore, we decided to build the chapters of this book in such a way that the students and other readers interested in noise control fields get a complete picture of the noise control subject in the following order:
•Chapter one defines the various characteristics of the term noise, units of noise measurements, definitions of sound pressure and sound power levels and their summation and relationships between them.
•While chapter two discusses in detail the various noise measuring variables available in the practice, permitted noise levels, as well as speech interference issue in front of high noise levels. The effects of noise on workers are also introduced. Standards available world-wide that are adopted in different countries, ISO Standard and OSHA regulations, are also introduced to calculate exposure times for particular nose levels.
•Methods of controlling noise at source is thus discussed in some details and the discussion of the principles of vibration isolation and thus the reduction in noise levels using suitable flexible mountings or vibration isolators is given in Chapter three.
•Chapter four shows lay-out of basic noise measuring systems and the various devices used for noise measurements, their technical specifications, standard noise measuring procedure, noise report and noise mapping are also described using suitable examples.
•Finally, chapter five introduces and methods of noise control at path using sound absorbing and barrier materials to avoid noise propagations in factories and rooms.
The above design of the topics covered in this syllabus was executed to fulfil the following objectives:
•To study fundamentals of sound and make basic calculations,
•To study effects of noise on workers and community; and study the various standards concerning the calculation of safe noise exposure time,
•To study methods of noise control at source; by isolating machine noise using flexible mountings
•To study noise measurements instruments, measurement standards, calibration, noise mapping and
•To study methods of noise control at path using absorbing materials, barriers, enclosures etc., and finally to study noise control at receiver using hearing protection devices.
To collect the materials of this book, a number of text books, references, manufacturers’ data sheets and brochures as well as published papers have been considered. To prepare suitable problems, the author had supervised a few final-year projects, also organised a number of training courses in Basics of Noise Control and made a number of experimental investigations in Aden Refinery Company, Aden Cement Enterprise, Badr Power Station, Al-Barh Cement Plant, to measure the noise levels at critical situations and prepared noise mapping in Aden Refinery Company to help the concerned authorities identifying noise problems and to take suitable measures to solve these problems.
This textbook has been written mainly for mechanical engineers, civil engineers, architects and students taking up courses in noise control. It explains the fundamentals of acoustics systematically and supplies a number of useful tables of acoustical materials illustrating their use. In this book, a few practical applications of noise problems at various industry sectors are considered
List of Contents:
Chapter 1:Characteristics of Sound 1
1.0 Introduction 1
1.1 Sound Propagation 1
1.2 Sound Velocity 4
1.3 Sound Power, Sound EnergyDensity and Intensity 6
1.4 The Logarithmic Scale Decibel 7
1.5 Sound Power Level 8
1.6 Sound Pressure Level 12
1.6.1Adding Equal Sound Pressure Levels 12
1.6.2 Adding Unequal Sound PressureLevels 14
1.7 Noise Spectrum 18
1.7.1 Octave Bands 20
1.7.2 One-third OctaveBands 24
1.8 Sound Reflection 24
1.9 Sound Diffraction 28
1.10 Sound Refraction 31
1.11 Sound Resonance 33
1.12 Sound Absorption 35
1.13 Sound Transmission Loss 36
1.14 Sound Sources 37
1.14.1The Plane Source 37
1.14.2The Point Source 37
1.14.3The Line Source 39
1.14.4Attenuation by Distance 40
1.15 Sound Pressure Level and SoundPower Level 44
1.16 Calculating Sound Power fromSound Pressure 53
Chapter 2: Effectsof Noise Exposure 61
2.0 Introduction 61
2.1 The Hearing Mechanism 67
2.2 Loudness Determination 71
2.3 Loudness of Short Duration 74
2.4 Age-related Hearing Loss –Presbycusis 77
2.5 Noise-induced Hearing Loss 78
2.5.1SteadyNoise 78
2.5.2Impulsive Noise 80
2.6 Subjective Rating Scales ofNoisiness and Annoyance 81
2.6.1Overall Sound Pressure Level dB 83
2.6.2A-weighted Sound Level 83
2.6.3Equivalent Continuous Sound Level 85
2.6.4Day-night Average Sound Level 86
2.6.5Noise Pollution Level 86
2.6.6Traffic Noise Index 87
2.6.7Perceived Noise Level 87
2.6.8Noise and Number Index 88
2.6.9Single Event Noise Exposure Level 88
2.7 Community Noise AnnoyanceCriteria 90
2.8 Speech Interference Criteria 95
2.9 Hearing Damage Risk Criteria ` 98
2.9.1Noise Exposure Limits 100
2.9.2OSHA Noise Regulations 109
Chapter 3: NoiseControl at Source 117
3.0 Introduction 117
3.1 Alteration of Machines andEquipment 120
3.1.1Machines 120
3.1.2Equipment 121
3.1.3Material Handling 122
3.1.4Surface Damping 123
3.1.5Other Simple Treatments 123
3.2 Vibration Isolation of Machines 124
3.2.1Principles of Noise Reduction 124
3.2.2Principles of Vibration Isolation 125
3.2.3Vibration Isolators & Compliance Characteristics 128
3.2.4Damping, Friction and Energy-dissipation Characteristics 130
3.2.5Calculation of Force Transmissibility 132
3.3 Selection of Vibration Isolators 146
3.3.1Vibration Isolation Efficiency 146
3.3.2Multi-degree of Freedom System, Coupled Modes 149
3.3.3Static Load Distribution Calculation 152
3.3.4Procedure for Selection of Vibration Isolators 154
Chapter 4 Noise Measurementsand Instruments 165
4.0 Introduction 165
4.1 Purpose of Noise Measurements 165
4.2 Frequency-weighting Networks 167
4.2.1Decibel Weighting Scales A, B and C 167
4.2.2Time Constants 170
4.3 Practical Noise MeasurementProcedure 172
4.3.1Determining Noise Measurement Positions in Closed Rooms 172
4.3.2Measurements in Open Air (Field Fields) 173
4.3.3Noise Mapping 174
4.4 Instruments for NoiseMeasurements 175
4.4.1Basic Noise Measuring Systems 175
4.4.2Portable Sound Level Meters 176
4.4.3Measuring Microphones 182
4.4.4Calibrations 189
4.4.5Noise Data Storage Systems 191
4.5 Laboratory Measurements andAnalysis 193
4.5.1Laboratory Measurements 193
4.5.2Field Measurements 196
4.6 External Influences on NoiseMeasurements 196
4.6.1Influence of Instrument and Operator 196
4.6.2Influence of the Environment 197
4.6.3Environmental Noise 198
4.7 Standardisation of NoiseMeasurements 203
4.7.1Measurement Reports 203
4.7.2Using Noise Rating Curves 204
4.7.3High-levels Noise 205
4.7.4General Rules to follow During Measurements 207
Chapter 5: NoiseControl Techniques 233
5.0 Noise Control 233
5.1 Sound Absorbing Materials 236
5.1.1Prefabricated Materials 236
5.1.2Blankets 236
5.1.3Acoustical Plasters 237
5.1.4Curtains 237
5.1.5Special Acoustical Arrangements 238
5.2 Recommended Noise Levels 239
5.3 Sound Absorption 244
5.3.1Sound Absorption Coefficient 244
5.3.2Noise Reduction 247
5.4 Reverberation of Sound 247
5.5 Shields & Barriers 255
5.5.1Barrier Design 257
5.5.2Noise Insulation Factor 263
5.6 Mass Laws of Barriers 269
5.6.1Transmission Loss of Single Wall Panels 271
5.6.2Transmission Loss of Double Wall Panels 272
5.7 Wood Structural Panels 274
5.7.1Single Wood Panels 275
5.7.2Double Wood Panels 277
5.8 Acoustical Enclosures 282
5.8.1Partial Enclosures 282
5.8.2Total Enclosures 285
5.8.3Ventilation of Enclosures 289
Appendices 297
Bibliography 339
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