Engineering Noise Control

Transcription

1 Engineering Noise Control Theory and practice Second edition David A. Bies and Colin H. Hansen Department of Mechanical Engineering University of Adelaide South Australia E & FN SPON An Imprint of Chapman & Hall London Glasgow Weinheim New York Tokyo Melbourne Madras

2 Contents Preface Acknowledgments xv xvii 1. Fundamentals and basic terminology Introduction Noise-control strategies Existing installations, facilities and products Installations, facilities and products in the design stage Airborne versus structure-borne noise The acoustic field variables and wave equation Variables The acoustic field Magnitudes The speed of sound Dispersion Acoustic potential function and the wave equation Plane and spherical waves Plane wave propagation Spherical wave propagation Mean square quantities Sound intensity Plane wave and far field intensity Spherical wave intensity Sound power Units Spectra Frequency analysis A convenient property of one-third octave band center frequencies Combining sound pressures 36

3 vi Contents Addition of coherent sound pressures Addition of incoherent sound pressures (logarithmic addition) Subtraction of sound pressure levels Combining level reductions Impedance Mechanical impedance, Z m Specific acoustic impedance, Z Acoustic impedance, Z A Flow resistance The human ear Brief description of the ear External ear Middle ear Inner ear Cochlear duct, or partition of the inner ear Subjective response to sound pressure level Loudness Loudness level in phons Comparative loudness and the sone Pitch Masking 60 3 Instrumentation for noise measurement and analysis Microphones Condenser microphone Piezo-electric microphone Pressure response Microphone sensitivity Field effects and calibration Weighting networks Sound level meters Grades of sound level meter Sound level meter calibration Electrical calibration Acoustical calibration Noise measurements using sound level meters Microphone mishandling Sound level meter amplifier mishandling Microphone and sound level meter response characteristics Background noise Wind noise 78

4 Contents Vll Temperature Humidity and dust Reflections from nearby surfaces Time-varying sound Noise level measurement Statistical analyzers Noise dose meters Tape recording of noise Spectrum analyzers Intensity meters Sound intensity by the p-u method Sound intensity by the p-p method Frequency decomposition of the intensity Criteria Introduction Hearing loss Threshold shift Presbyacusis Hearing damage Hearing damage risk Requirements for speech recognition Quantifying hearing damage risk International Standards Organization formulation Alternative formulations Observed hearing loss Some alternative interpretations Hearing damage risk criteria Continuous noise Impulse noise Impact noise Speech interference criteria Broadband background noise Intense tones Psychological effects of noise Noise as a cause of stress Effect on behavior and work efficiency Ambient noise level specification Noise weighting curves Comparison of specifications Speech privacy Community noise level criteria A-weighting criteria Noise rating criteria 126

5 viii Contents 5. Sound sources and outdoor sound propagation Introduction Simple source Pulsating sphere Fluid mechanical monopole source Dipole source Pulsating doublet (far-field approximation) Vibrating sphere Fluid mechanical dipole source Quadrupole source (far-field approximation) Lateral quadrupole Longitudinal quadrupole Fluid mechanical quadrupole source Line source Infinite line source Finite line source Piston in an infinite baffle Far field Near field on axis Radiation load of the near field Incoherent plane radiator Single wall Several walls of a building or enclosure Directivity Reflection effects Simple source near a reflecting surface Observer near a reflecting surface Observer and source both close to a reflecting surface Reflection and transmission at a plane/two media interface Porous earth Plane wave reflection and transmission Spherical wave reflection at a plane interface Effects of turbulence Sound propagation outdoors, general concepts Review of methodology Limits to accuracy of prediction Forecasting schemes Geometrical spreading Directivity index Excess attenuation factor Air absorption Shielding by barriers 173

6 Contents Attenuation due to forests Ground effects Image inversion and increased attenuation at large distance Meteorological effects 185, Sound power, its use and measurement Introduction Radiation impedance Relation between sound power and sound pressure Radiation field of a sound source Free-field simulation in an anechoic room Sound field produced in an enclosure Determination of sound power using intensity measurements Determination of sound power using conventional pressure measurements Measurement in free or semi-free field Measurement in a diffuse field Field measurement Determination of sound power using surface vibration measurements Some uses of sound power information The far free field The near free field 220 Sound in enclosed spaces Introduction Wall-cavity modal coupling Sabine rooms Flat and long rooms Low frequencies Bound between low-frequency and high-frequency behavior Modal density Modal damping and bandwidth Modal overlap Cross-over frequency High frequencies, statistical analysis Effective intensity in a diffuse field Energy absorption at boundaries Air absorption Steady-state response Transient response 237 ix

7 X Contents Classical description Modal description Mean free path Measurement of the room constant Reference sound source method Reverberation time method Porous sound absorbers Measurement of absorption coefficients Porous liners Porous liners with perforated panel facings Sound absorption coefficients of materials in combination Panel sound absorbers Empirical method Analytical method Flat and long rooms Flat room with specularly reflecting floor and ceiling Flat room with diffusely reflecting floor and ceiling Flat room with specularly and diffusely reflecting boundaries Long room with specularly reflecting walls Long room with circular cross-section and diffusely reflecting wall Long room with rectangular cross-section Applications of sound absorption Relative importance of the reverberant field Reverberation control Optimizing reverberation control Acoustic enclosures and barriers Introduction Sound transmission through partitions Bending waves Transmission loss Panel transmission loss Double wall transmission loss Common building materials Sound-absorptive linings Composite transmission loss Enclosures Noise inside enclosures Noise outside enclosures 308

8 Contents XI Personnel enclosures Enclosure windows Enclosure leakages Access and ventilation Enclosure vibration isolation Enclosure resonances Close-fitting enclosures Partial enclosures Barriers Diffraction at the edge of a thin sheet Outdoor barriers Indoor barriers Pipe lagging 332 / Porous material lagging Impermeable jacket and porous blanket lagging Muffling devices Introduction Measures of performance Diffusers as muffling devices Classification of muffling devices Acoustic impedance Lumped element devices Impedance of an orifice or a short narrow duct Impedance of a volume Reactive devices Acoustical analogs of Kirchoff s laws Side branch resonator Expansion chamber Small engine exhaust Lowpass filter Pressure drop calculations for reactive muffling devices Flow-generated noise Lined ducts Locally reacting and bulk reacting liners Liner specification Lined duct silencers Cross-sectional discontinuities Pressure drop calculations for dissipative mufflers Duct bends Unlined ducts Effect of duct end reflections Duct break-out noise 391

9 Xll Contents Break-out sound transmission Break-in sound transmission 9.13 Lined plenum attenuator 9.14 Water injection 9.15 Directivity of exhaust ducts Vibration control Introduction Vibration isolation Single-degree-of-freedom systems Multi-degree-of-freedom systems Damping, stiffness and mass relationships Lack of stiffness of equipment mounted on isolators Lack of stiffness of foundations Superimposed loads on isolators Types of isolators Rubber Metal springs Cork Felt Air springs Vibration absorbers Vibration measurement Acceleration transducers Velocity transducers Instrumentation systems Units of vibration Damping of vibrating surfaces When damping is effective and ineffective Damping methods Measurement of damping Sound power and sound pressure level estimation procedures Introduction Fan noise Air compressors Small compressors Large compressors (noise levels within the inlet and exit piping) Large compressors (exterior noise levels) Compressors for refrigeration units Cooling towers 440

10 Contents 11.6 Pumps Jet noise General estimation procedures Gas and steam vents General jet noise control Control valve noise Internal sound power generation Internal sound pressure level External sound pressure level Control valve noise reduction Control valves for liquids Control valves for steam Pipe flow noise Boiler noise Turbine noise Diesel and gas-driven engines Exhaust noise Casing noise Inlet noise Furnace noise Electrical motor noise Small electric motors (below 300 kw) Large electric motors (above 300 кw) Generators Transformers Gear noise Active noise control Introduction Active control of sound propagation in ducts Active control of plane wave propagation Active control of higher order mode propagation Periodic feedforward controller Random noise feedforward controller Feedback controller Control sound sources Microphones Active control of sound radiation from vibrating structures Physical control mechanisms Control actuators and error sensors Sound transmission into enclosed spaces Active vibration isolation Electronic controller design 491 хш

11 xiv Contents 13 Survey of analytical techniques for the estimation of sound power levels Introduction Low-frequency region Helmholtz method Rayleigh method Simple acoustic modeling High-frequency region 501 Appendix A Problems 502 Appendix В Properties of materials 512 Appendix С Acoustical properties of porous materials, 514 Appendix D Absorption coefficients based upon impedance tube measurements 521 Appendix E Porous liners 526 Appendix F Frequency analysis 530 References 546 List of Acoustical Standards 559 Glossary of symbols 568 Index 589