THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

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188 9. Sound-Measuring InstrumentationFigure 9.11. Schematic of a noise dosimeter.The noise dosimeter is a device designed to measure the percentage of the maximumdaily noise dose permitted by regulations. Its functional elements are givenin Figure 9.11. Both the noise dosimeter and the personal sound exposure metershare the same requirements for operation under severe operating conditions; andboth types of instruments include a microphone, an amplifier, A-weighting network,a squaring device, a time integrator, and an indicator. The personal soundexposure meters contain a latching overload but the noise dosimeter may includea latching upper-limit indicator. Additionally, the dosimeter must include exponentialtime-weighting usually incorporating the slow-response characteristic anda manufacturer-specified threshold sound level, 1 neither of which is found in thepersonal sound exposure meter.American National Standard ANSI S1.25 gives the specifications for a noisedosimeter. Slow-time weighted, A-weighted sound pressure is integrated with a5-dB exchange rate 2 in accordance with the regulations of U.S. OccupationalSafety and Health Administration (OSHA, 1983) and Mine Safety and Health1 Threshold sound level, stated in decibels, is the A-weighted sound level specified by the manufacturerof the noise dosimeter below which the instrument provides no significant indication. The thresholdsound level should be at least 5 dB less than the criterion sound level.2 The terminology exchange rate, expressed in decibels, refers to the change in decibels required todouble (or halve) the exposure time in order to maintain the same amount of noise exposure. Forexample, with the 5 dB exchange rate, exposure to 90 dB for 8hisequivalent to exposure to 95 dBfor4horto100dBfor2h.
9.11 Noise Measurement in Selected Frequency Bands, Band Pass Filters 189Administration (MSHA, 1982). The exchange rate may also be 3 or 4 dB dependingon the application. ANSI S1.25 also specifies limits for the effects of changes inair pressure, temperature, vibration, and magnetic field on the noise dosimeter.The British standard BS 6402 calls for a personal sound level meter to measuresound exposure, i.e., the timed-integrated A-weighted sound pressure level witha 3-dB exchange rate and without exponential time weighting (British StandardsInstitution, 1983). A latching overload indicator is also mandated by the Britishstandard to provide warning that the sound level received at the microphone hasexceeded the measuring range of the instrument (up to 132 dB peak).An IEC international standard for personal sound exposure meters defines awider operating range for a Type-2 integrating averaging SLM. Under this specification,measurements are made of the exposures produced by impulsive, fluctuating,and intermittent sounds over a range of A-weighted sound levels from 80 dBto 130 dB. Excessive input sound levels should trigger the mandatory overloadindicator.9.11 Noise Measurement in Selected Frequency Bands,Band Pass FiltersA valuable means of analyzing noise is the evaluation of sound in each frequencyband. If a machine emits a noise that indicates it is malfunctioning, the analysisof the sound output according to frequency can provide vital clues as to whichcomponent of the machine is defective. This situation calls for the use of aspectrum analyzer, which is a device that analyzes a noise signal in the frequencydomain by electronically separating the signal into various frequency bands. Thisseparation is executed through the use of a set of filters. A filter is a two-portelectrical network with a pair of terminals at each port. A filter can be constructedwith as few as two passive electrical components (e.g., a resistor and a capacitor),or it can be more complex involving a large number of passive components, or acombination of passive elements operating in conjunction with active components(e.g., op amps). Analog filters embody electronic circuitry tuned to pass certainfrequencies, whereas digital filters make use of active electronic elements.Figure 9.12 illustrates the effects of ideal and real filters. An ideal bandpassfilter is a circuit that transmits only that part of the input signal within its bandpass( f 1 ≤ f ≤ f 2 ) and completely attenuates all of the components at all frequenciesoutside of the bandpass ( f ≤ f 1 and f ≥ f 2 ). The ideal low-pass filter passes allsignals up to frequency f lp and rejects all signals having frequencies above f lp .The ideal high-pass filter passes all signals above frequency f hp and rejects all ofthe contents of the input signal below f hp . In the real world, filters alter the shapesof the input signals to some degree. The amplitude and phase characteristics of thefilter can be ascertained by computing the transfer function (or filter response),which is the ratio of the filter output to the filter input for all possible values offrequency. Both ideal and actual frequency responses are shown in Figure 9.12.The actual filters have characteristics of the form shown on the right-hand side
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THE SCIENCE ANDAPPLICATIONS OFACOUS
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xPrefaceReferencesBacon, Sir Franci
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xiiContents16. Ultrasonics 44317. C
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2 1. A Capsule History of Acoustics
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1. A Capsule History of Acoustics 5
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12 1. A Capsule History of Acoustic
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14 2. Fundamentals of AcousticsFigu
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16 2. Fundamentals of Acoustics2.2
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18 2. Fundamentals of Acousticsof t
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20 2. Fundamentals of AcousticsQ z+
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22 2. Fundamentals of Acousticsin t
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24 2. Fundamentals of AcousticsWe c
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26 2. Fundamentals of Acoustics(2)
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28 2. Fundamentals of AcousticsEqua
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30 2. Fundamentals of Acoustics11.
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32 3. Sound Wave Propagation and Ch
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3.14 Performance Indices for Enviro
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3.14 Performance Indices for Enviro
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or in terms of complex exponential
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3.17 Sound Intensity 61Here the sur
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3.18 The Monopole Source 63The thre
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3.21 Energy Density 653.20 The Hemi
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References 67medium. The time avera
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Problems for Chapter 3 69(a) the wa
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4Vibrating Strings4.1 IntroductionI
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4.4 General Solution of the Wave Eq
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4.6 Simple Harmonic Solutions of th
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4.7 Standing Waves 77Figure 4.3. Di
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4.8 The Effect of Initial Condition
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4.10 Forced Vibrations in an Infini
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4.11 Strings of Finite Lengths: For
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References 854.12 Real Strings: Fre
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Problems for Chapter 4 878. A devic
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90 5. Vibrating BarsFigure 5.1. A b
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92 5. Vibrating BarsSettingc 2 = E/
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94 5. Vibrating BarsThe allowable f
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96 5. Vibrating Barsthe acceleratio
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98 5. Vibrating BarsFigure 5.5. Loc
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100 5. Vibrating Barsmore difficult
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102 5. Vibrating BarsFigure 5.7. An
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104 5. Vibrating Barsthe light beam
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106 5. Vibrating BarsFigure 5.8. Tr
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108 5. Vibrating BarsFigure 5.10. T
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110 5. Vibrating Barsof 0.005 m dia
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112 6. Membrane and PlatesFigure 6.
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114 6. Membrane and PlatesBecause t
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116 6. Membrane and PlatesThe left-
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118 6. Membrane and PlatesTable 6.1
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120 6. Membrane and PlatesIn real a
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122 6. Membrane and PlatesTable 6.2
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124 6. Membrane and PlatesAt low fr
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126 6. Membrane and PlatesThe elast
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128 6. Membrane and PlatesFor the f
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130 6. Membrane and Plates(b) Deter
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132 7. Pipes, Waveguides, and Reson
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134 7. Pipes, Waveguides, and Reson
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Page 181 and 182: 9Sound-Measuring Instrumentation9.1
Page 183 and 184: 9.3 Microphones 175Figure 9.1. A cu
Page 185 and 186: SolutionEquation (9.3) is applied t
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Page 189 and 190: 9.6 Vector Sound Intensity Probes 1
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Page 195: Example Problem 39.10 Dosimeters 18
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Page 201 and 202: 9.12 Real Time Analysis 193analyzer
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Page 207 and 208: 9.16 Measurement Error 199whereβ =
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Page 217 and 218: References 209acoustical output and
Page 219 and 220: Problems for Chapter 9 2112. Determ
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240 10. Physiology of Hearing and P
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11Acoustics of Enclosed Spaces:Arch
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11.2 Sound Fields 245Figure 11.1. P
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11.4 Sound Intensity Growth in a Li
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11.5 Sound Absorption Coefficients
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11.6 Growth of Sound with Absorbent
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11.7 Decay of Sound 253Following Sa
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11.8 Decay of Sound in Dead Rooms 2
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11.9 Reverberation as Affected by S
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11.13 Sound Levels due to Direct an
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11.15 Concert Halls and Opera House
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Figure 11.9. A view of the Boston S
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11.16 Band Shells and Outdoor Audit
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11.16 Band Shells and Outdoor Audit
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11.17 Subjective Preferences in Sou
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References 277preferred subsequent
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Problems for Chapter 11 279Siebein,
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12Walls, Enclosures, and Barriers12
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12.3 Mass Control Case 283Figure 12
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12.5 Effect of Frequencies on Sound
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12.6 Coincidence Effect and Critica
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12.7 The Double-Panel Partition 289
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an ideal gas) varies in the followi
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12.8 Measuring Transmission Loss 29
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12.10 Combined Sound Transmission C
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12.11 Noise Insulation Ratings 297F
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12.11 Noise Insulation Ratings 299s
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12.12 Noise Reduction of a Wall 301
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12.12 Noise Reduction of a Wall 303
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12.14 Enclosures 305to the extent t
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12.14 Enclosures 307and similarly f
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12.15 Small Enclosures 309walls. Ac
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12.16 Acoustic Barriers 311Figure 1
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12.16 Acoustic Barriers 313In the c
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Equation (12.67) becomes(11D = λ+
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Problems for Chapter 12 3173. A 0.7
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13Criteria and Regulations forNoise
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13.3 The Occupational Safety and He
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13.4 Perception of Noise 323inspect
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13.6 Indoor Noise Criteria 325accou
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13.6 Indoor Noise Criteria 327Room
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13.7 Equivalent Sound Level, Day-Ni
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13.7 Equivalent Sound Level, Day-Ni
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Composite Noise Rating13.9 Rating o
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13.10 Evaluation of Traffic Noise 3
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Highway Construction Noise13.10 Eva
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13.11 Evaluation of Community Noise
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13.12 Guidelines and Regulations in
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References 353Computer Program, HIC
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Problems for Chapter 13 355Problems
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14Machinery Noise Control14.1 Intro
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14.4 Fan or Blower Noise 359Table 1
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14.4 Fan or Blower Noise 361Figure
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14.6 Pumps and Plumbing Systems 367
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14.6 Pumps and Plumbing Systems 369
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14.8 Gears 371fromwheref BRC = N r
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14.8 Gears 373Figure 14.7. Gear noi
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14.8 Gears 375Figure 14.8. Gear tra
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14.8 Gears 377The subscripts 1 and
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14.10 Ball and Roller Bearings 379l
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14.10 Ball and Roller Bearings 381c
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14.11 Other Mechanical Drive Elemen
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Belt Drivesf CL = n 1N 1 2400 × 12
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14.12 Gas-Jet Noise 387said to be c
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14.12 Gas-Jet Noise 389power discha
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Solution14.12 Gas-Jet Noise 391Usin
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14.13 Gas Jet Noise Control 393Solu
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14.13 Gas Jet Noise Control 395Figu
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14.13 Gas Jet Noise Control 397Figu
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14.14 Mufflers and Silencers 399Fig
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(1 + m)A I 1=A 314.14 Mufflers and
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14.14 Mufflers and Silencers 403Let
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References 405Figure 14.21 illustra
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Problems for Chapter 14 407the nois
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15Underwater Acoustics15.1 Sound Pr
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15.3 Speed of Sound in Seawater 411
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15.4 Velocity Profiles in the Sea 4
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15.4 Velocity Profiles in the Sea 4
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15.5 Underwater Transmission Loss 4
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15.6 Parametric Variation of Absorp
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15.8 Underwater Refraction 421Figur
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15.9 Mixed Layer 423When G is const
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15.11 Sonar Transducers and Their P
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Example Problem 115.12 The Sonar Eq
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Active and Passive Equations15.12 T
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15.13 Noise, Echo, and Reverberatio
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15.13 Noise, Echo, and Reverberatio
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15.14 Transient Form of Sonar Equat
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Example Problem 315.16 Shortcomings
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15.17 Theoretical Target Strength o
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Problems for Chapter 15 441Wilson,
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444 16. Ultrasonicscatching small i
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446 16. UltrasonicsPlanck constant
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448 16. UltrasonicsEquation (16.5)
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450 16. UltrasonicsFigure 16.1. Sou
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452 16. Ultrasonicsthe positive hal
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454 16. Ultrasonicson each and ever
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456 16. Ultrasonicscomplete as a li
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458 16. Ultrasonicsinitial of their
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460 16. Ultrasonicsoptic axis, deno
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462 16. Ultrasonicstransducer, it h
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464 16. UltrasonicsTable 16.1. Valu
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466 16. Ultrasonicsthe mechanical r
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468 16. UltrasonicsThe Physics of M
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470 16. UltrasonicsFigure 16.7. The
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472 16. Ultrasonicscurvilinear arra
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474 16. Ultrasonics(a)amplitudeinpu
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476 16. Ultrasonicsslow to allow th
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478 16. Ultrasonics5. In the cases
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480 17. Commercial and Medical Ultr
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510 18. Music and Musical Instrumen
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Figure 18.7. The frequencies of the
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Figure 18.20. The violin octet deve
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570 19. Sound ReproductionAlbert, a
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572 19. Sound ReproductionD. Magnet
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574 19. Sound Reproductionon, machi
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576 19. Sound ReproductionIt is fai
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578 19. Sound ReproductionINNER SUS
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580 19. Sound Reproductiontuned ape
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582 19. Sound Reproductionuse of MP
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584 19. Sound ReproductionDickason,
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586 20. Vibration and Vibration Con
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618 21. Nonlinear Acousticsby∇ 2
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620 21. Nonlinear Acousticsmay be i
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622 21. Nonlinear Acousticswhereδ
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624 21. Nonlinear AcousticsThe shoc
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626 21. Nonlinear AcousticsBut the
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Appendix APhysical Properties of Ma
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Appendix A. Physical Properties of
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Appendix BBessel FunctionsB.1 The B
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B.8 Tables of Bessel Functions, Zer
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Appendix CUsing Laplace Transforms
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C.3 Solving Differential Equations
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C.4 Equations with Multiple-Order R
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SolutionC.5 Equations with Complex
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C.5 Equations with Complex Roots 64
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SolutionC.5 Equations with Complex
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650 IndexAuditoriums, design of, 26
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652 IndexElectrostatic speakers, 58
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654 IndexKey notation, 518Kinetic e
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656 IndexPascal (unit), 48Percent i
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658 IndexSound intensity growth in
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660 IndexWater-hammer arresters, 37
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