Introduction to Acoustics

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Microphone, amplifier and A/D converter Microphone, amplifier and A/D converter Microphone, amplifier and A/D converter Microphone, amplifier and A/D converter Microphone, amplifier and A/D converter Microphone, amplifier and A/D converter Microphone, amplifier and A/D converter Microphone, amplifier and A/D converter Digital signal processor and storage device Fig. 23.7 Block diagram of a multichannel instrument using digital signal processing such as the sound level exceeded at various percentages of a time interval, e.g., 10% of the time in an hour of observations. Performance specifications for the measurement of percentile sound level are not standardized, and the results may vary depending on the manufacturer of the instrument and the percentile of interest, with the greatest variations at the extremes of the percentiles. 23.1.7 Multichannel Instruments Many applications for noise control are best satisfied by use of a microphone array. These include measurement of sound pressure level at multiple positions on a measurement surface for determination of sound power, and measurements at several locations around a time-varying sound source. In the first case, several microphones may be connected to a multiplexer, and the outputs sampled sequentially. In the second case, the microphones may each be connected to an amplifier and analog-to-digital pA mike pB ∆r Add inputs Pre-amp Filter Sums mike Pre-amp Filter Integrate Subtract inputs Noise 23.1 Instruments for Noise Measurements 969 (A/D) converter. High sampling rates (e.g., greater than 40 kHz) are required. The data are sent to a digital signal processor and storage device, for example, a digital computer. A block diagram of such a system is shown in Fig. 23.7. The number of samples of sound pressure level data that can be stored in a multichannel measurement system depends on the available storage capacity, which can be quite large in the case of systems used for monitoring noise in the community and around airports. 23.1.8 Sound Intensity Analyzers Sound intensity is covered in detail in Chap. 25. Sound intensity analyzers often use two closely spaced microphones to approximate the pressure gradient in a sound field. Particle velocity is found by integration of the time derivative of the sound-pressure gradient (23.3). Sound pressure is the average of the pressures at the two microphones. A block diagram of a sound intensity meter isshowninFig.23.8. Processing of the sampled signals may be accomplished either with analog circuits or digitally. Standards for sound intensity analyzers are available [23.11, 12]. 23.1.9 FFT Analyzers Unlike octave-band and one-third-octave band filters, which are proportional (or constant-percentage) bandwidth filters, a fast Fourier transform (FFT) analyzer is essentially a set of fixed-bandwidth filters. The FFT is a computational implementation of the discrete Fourier transform that produces a set of discrete-frequency spectral lines. The number of spectral lines in a given frequency interval depends on the number of samples of the time series obtained from digital sampling of the sound-pressure signal. If a periodic wave is sampled A/D converter A/D converter ( pA + pB)/2 u Product Average and calculate Fig. 23.8 Block diagram of an analog-to-digital sound intensity analyzer with octave-band filters. Alternatively, the preamplifier outputs of the microphones could be suitably amplified and converted to digital format; all further processing would then be done digitally Out Part G 23.1
970 Part G Structural Acoustics and Noise Part G 23.2 with a sampling period that is not an integral number of wavelengths of the wave, spectral leakage occurs. FFT analyzers contain windows to improve spectral estimates – the Hanning window is the most common. There are no 23.2 Noise Sources In this section, methods for the specification of noise emissions are given, noise emission criteria are described, and some basic principles of noise control are presented. A general description of noise control for stationary sources is presented, and some information on vehicle noise and aircraft noise is given. A short section on the principles of active noise control is included. 23.2.1 Measures of Noise Emission This section is an edited version of a textbook chapter of [23.13]. Two quantities are needed to describe the strength of a noise source, its sound power level and its directivity. The sound power level is a measure of the total sound power radiated by the source in all directions and is usually stated as a function of frequency, for example, in one-third octave bands. The sound power level is then the preferred descriptor for the emission of sound energy by noise sources. The directivity of a source is a measure of the variation in its sound radiation with direction. Directivity is usually stated as a function of angular position around the acoustical center of the source and also as a function of frequency. From the sound power level and directivity, it is possible to calculate the sound pressure levels produced by the source in the acoustical environment in which it operates. In Sect. 23.3.2, a classical method for this calculation is presented – as is an alternative method for long and flat rooms. A source may set a nearby surface into vibration if it is rigidly attached to that surface, causing more sound power to be radiated than if the source were vibration isolated. Both the operating and mounting conditions of the source therefore influence the amount of sound power radiated as well as the directivity of the source. Nonetheless, the sound power level alone is useful for: comparing the noise radiated by machines of the same type and size as well as by machines of different types and sizes; determining whether a machine complies with a specified upper limit of noise emission; planning in national or international standards for the performance of FFT analyzers. The results of measurements by FFT analyzers may vary depending on the design implementation by the manufacturer or computer programmer. order to determine the amount of transmission loss or noise control required; and engineering work to assist in developing quiet machinery and equipment. Expanding the dot product in (23.6) allows the surface integral to be written in terms of scalar quantities � W = In dS , (23.21) S where In = I cos(θ) is the component of sound intensity normal to the surface at the location of dS; dSis the magnitude of the elemental surface area vector. The integral may be carried out over a spherical or hemispherical surface that surrounds the source. Other regular surfaces, such as a parallelepiped or a cylinder, are also used in practice, and, in principle, any closed surface can be used. If the source is nondirectional and the integration is carried out over a spherical surface having a radius r and centered on the source, sound intensity and sound power are related by I(at r) = In(at r) = W W = , (23.22) S 4πr2 where I is the magnitude of intensity on the surface (at radius r), In is the normal component of intensity on the surface (at radius r), W is the sound power, S is the area of spherical surface (4πr 2 ), and r is the radius of the sphere. In general, a source is directional, and the sound intensity is not the same at all points on the surface. Consequently, an approximation must be made to evaluate the integral of (23.21). It is customary to divide the measurement surface into a number of subsegments, each having an area Si, and to approximate the normal component of the sound intensity on each surface subsegment. The sound power of the source may then be calculated by a summation over all of the surface subsegments: W = � IniSi , (23.23) i here Ini is the normal component of sound intensity averaged over the i-th area segment, Si is the i-th area segment, and i is the number of segments.
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Springer Handbook of Acoustics
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Springer Handbook of Acoustics Thom
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Foreword The present handbook cover
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List of Authors Iskander Akhatov No
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Philippe Roux Université Joseph Fo
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XIV Contents 3.7 Attenuation of Sou
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XVI Contents 10 Concert Hall Acoust
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XVIII Contents 17.8 Physical Modeli
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XX Contents 24.5 Free-Field Microph
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XXII List of Abbreviations K KDP po
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Introduction 1. Introduction to Aco
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of noise have been the subject of c
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in order to understand how objectiv
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A Brief 2. A Brief History of Acous
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of 350 m/s for the speed of sound [
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number and relative strength of its
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To his contemporaries, Koenig was p
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Probably the most important use of
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piezoelectric ceramic compositions
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surveys together [2.46]. Masking of
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ther of computer music, since he de
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Basic 3. Linear Basic Linear Acoust
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M average molecular weight n unit v
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a) b) S v.n ∆t ∆S V |v| ∆t n
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temperature, q =−κ∇T , (3.16)
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The equivalent density M/V is conse
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Basic Linear Acoustics 3.3 Equation
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Because any vector field may be dec
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The latter and (3.84), in a manner
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assumed to have no ambient motion,
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Because the friction associated wit
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3.5 Waves of Constant Frequency One
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3.5.4 Time Averages of Products Whe
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as well as symmetry considerations,
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The auxiliary internal variables th
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Then the transient at a distant pos
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ω ′ = 0, and this is consistent
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1.0 10 -1 10 -2 10 -3 10 -4 10 -5 A
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This yields the interpretation that
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direction of propagation when a pla
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so the time-averaged incident energ
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Although the simple result of (3.31
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ut, also in keeping with the linear
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equation, the two differential equa
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Rodrigues relation, one has �1
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for the derivative.) In the asympto
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The differential scattering cross s
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elow) is F(t) = (2c) 1/2 �t −
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0.5 0 -0.5 -1.0 -1.5 0 Y0(η) (π/2
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is the Wronskian for the Bessel and
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The function qS is termed the sourc
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The appropriate identification for
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where jℓ is the spherical Bessel
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this subtlety taken into account, o
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U(x) Basic Linear Acoustics 3.15 Wa
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is ordinarily valid. With these ass
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along rays. These can be regarded a
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A(x0) x0 A(x) Fig. 3.53 Sketch of a
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possible, and one where neither the
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which is independent of the z-coord
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[3.108], and Carslaw [3.109]. In th
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where C(X)andS(X) are the Fresnel i
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Fig. 3.60 Characteristic diffractio
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of elastic solids, Trans. Camb. Phi
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3.101 J.B. Keller: Geometrical acou
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114 Part A Propagation of Sound Par
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Underwater 5. Underwater Acoustics
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5.1 Ocean Acoustic Environment The
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Long-Range Propagation Paths Figure
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tal direction, there is no loss ass
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equivalent circuit, as shown in Fig
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Attenuation á (dB/km) 1000 100 10
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5.2.5 Ambient Noise There are essen
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ubble natural acoustic resonance ω
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a bubbly medium (and for the simple
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As discussed, because detection inv
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(1/A)∇ 2 A ≪ K 2 )sothat(5.34)
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water, where the deep sound channel
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egion in the form p(r, z) = ψ(r, z
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5.4.6 Propagation and Transmission
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tegration interval. The source puls
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5.6 SONAR Array Processing Signal p
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former output is: �∞ b(θ,t) =
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Fig. 5.37 Angle-versus-time represe
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5.7 Active SONAR Processing Depth M
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a factor when there is a reverberan
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depth measurements that correspond
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along the cross-shelf track taken b
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time as a result of multiple paths,
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technique is very sensitive, and ex
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Fig. 5.57a,b Typical echogram obtai
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Frequency (Hz) 150 100 50 0 0 a) b)
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out. These data allow for study of
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5.59 G. Raleigh, J.M. Cioffi: Spati
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Physical 6. Physical Acou Acoustics
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where I is the intensity of the sou
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Wave velocity The wall exerts a dow
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destructively interfered with one a
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or: � � p2 � rms SPL = 10 log
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6.1.4 Wave Propagation in Solids Si
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where c is again the wave speed and
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measured. Some resonances are cause
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as 50 µmto5µm through one oscilla
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the number of false positives and m
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with the small mass), and frequency
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Laser Lens 1 Circular aperture Fig.
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Ground ring Insulator Sample Resist
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Energy ratio 1.0 0.8 0.6 0.4 Calcul
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terms. In this equation γ is the r
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directly. The nonlinearity paramete
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Thermoacoust 7. Thermoacoustics The
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Table 7.1 The acoustic-electric ana
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walls of the pores. (Positive G ind
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a) b) c) C reso d) δtherm e) p 0 U
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a) b) UA,l c) d) E 0 Q A Q A TA TA
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tor. This eliminates the need to le
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to this consumption of acoustic pow
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The traditional Stirling refrigerat
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Washington 1986) pp. 550-554, Softw
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258 Part B Physical and Nonlinear A
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Acoustics 9. Acoustics in Halls for
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parameters, so we can assist in bui
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weeks or even years is less reliabl
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9.3.1 Reverberation Time Reverberan
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selected). A distance different fro
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ing sound, as will naturally be exp
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of the sound fields. Consequently,
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e derived from interrupted noise de
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Acoustics in Halls for Speech and M
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espectively, can be calculated from
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ated by the architects. However, on
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of C and G. However, as all the ind
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F b d F n I S Fb Fn S d F n/F b d/d
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HS S èn ã d0 P0 rn Position of ey
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Time T (s) 2.5 2 1.5 1 5 10 15 Acou
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floor can be tilted to reduce volum
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ÄLcurv (dB) 10 8 6 4 2 0 -2 -4 -6
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Seating capacity 2662 1 915 + 324 2
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4 3 2 1 Acoustics in Halls for Spee
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cially in auditoria with T values l
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esonance (AR)andmultichannel reverb
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Concert 10. Concert Hall Acoustics
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Concert Hall Acoustics Based on Sub
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0 0 Concert Hall Acoustics Based on
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mately by Concert Hall Acoustics Ba
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10.1.5 Specialization of Cerebral H
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The other (n − 1) bits indicated
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As for the conflicting requirements
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have mainly been concerned with tem
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a) c) S S -4.3 -2.8 -2.0 -3.5 -3dB
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a model of the auditory-brain syste
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Building 11. Building Acou Acoustic
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Pressure Maximum Minimum 0 D Distan
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Table 11.1 Absorption coefficients
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Absorption coefficient α 1 0 Frequ
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is of key importance in rooms where
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Table 11.4 Transmission loss and ST
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TL of wall - (TL of door, window or
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Table 11.7 Generalized noise reduct
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Masking sound pressure level (dB) 5
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As for the room criterion (RC) meth
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11.5 Noise Control Methods for Buil
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Neoprene pads (30 durometer) with a
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Concrete Caulk around perimeter Vib
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Trim board to conceal gap (fasten o
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Gypsum board partition (as schedule
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Double-layer ribbed or waffle neopr
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11.6 Acoustical Privacy in Building
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Table 11.9 AI,SIIandPIforopenplanof
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Electronic sound masking in plenum
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E 1179 Standard Specification for S
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430 Part D Hearing and Signal Proce
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Psychoacoust 13. Psychoacoustics Ps
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Absolute threshold (dB SPL) 100 90
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the signal. By using this off-cente
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is as a crude indicator of the exci
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Relative response (dB) 100 90 80 70
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In a variation of this procedure, t
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Level of matching noise (dB) 100 90
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13.4 Temporal Processing in the Aud
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Most models include an initial stag
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The components were either uniforml
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(Frequency DL)/ERBN 0.2 0.1 0.05 0.
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elaborate place models have been pr
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13.6 Timbre Perception 13.6.1 Time-
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the duplex theory of sound localiza
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harmonic (by shifting the frequency
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sive. While some studies have been
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sentences (see Fig. 13.20). They va
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components is usually only perceive
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References 13.1 ISO 389-7: Acoustic
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13.74 D. Ronken: Monaural detection
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asymmetric function, J. Acoust. Soc
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13.211 J. Vliegen, A.J. Oxenham: Se
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534 Part E Music, Speech, Electroac
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The 16. The Human Human Voice in Sp
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uation, the effect of gravity is in
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piratory muscles (the internal inte
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Mean Ps (cm H2O) 50 40 30 20 10 0 D
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Glottal flow Closed Opening Open Cl
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Transglottal airflow (l/s) 0.4 0.2
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Mean spectrum level (dB) -30 -40 -5
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20 10 0 -10 -20 -30 -40 -50 0 i y u
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Mean level (dB) 0 -10 -20 -30 -40 1
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This topic was addressed by Ladefog
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Fig. 16.29 Acoustic consequences of
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Bass i e u Alto Tenor o ε œ æ Th
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100 80 60 40 20 0 -20 100 80 60 40
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tours for [� ]and[Ù ] sampled at
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Rapp [16.100] asked three native sp
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Utterance command T0 T3 Accent comm
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The # symbol indicates the possibil
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Second formant frequency (Hz) 2500
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tional rather than absolute (à la
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16.7 P. Ladefoged, M.H. Draper, D.
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esonance imaging: Vowels, J. Acoust
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16.139 A. Eriksson: Aspects of Swed
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Computer 17. Computer Mu Music This
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Quantum step Amplitude Quantization
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Some might notice that linear inter
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pers, textbooks, patents, etc. Furt
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0:00.0 0.5 0 Computer Music 17.3 Ad
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(0,0) (0,1) (1,1) (0,2) (1,2) (0,3)
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synthesizing vocoder. The main diff
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x(n) + z -1 z -1 Scattering junctio
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230 Hz FOF 1100 Hz FOF 1700 Hz FOF
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0 y + - Computer Music 17.8 Physica
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-1 (1-ß )×length Velocity + Veloc
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0 -30 (dB) -60 0 1.5 3 4.5 (kHz) Fi
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17.10 Composition The history of co
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and variance of the features can be
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17.20 J.L. Kelly Jr., C.C. Lochbaum
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Audio 18. Audio and Electroacoustic
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Alexander Graham Bell filed his pat
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on magnetic stripes. A common arran
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60 40 20 0 SPL-sound pressure level
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Interaural intensity difference (dB
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with equalization, without incurrin
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Fig. 18.8 Sine wave with crossover
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18.3.8 Dynamic Range Dynamic range
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Directly actuated type Diaphragm ty
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effective pickup pattern of the arr
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attempts to apply complementary com
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Most of the issues relating to spea
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nificant design considerations. At
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Some appreciation of the performanc
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pre-digital reverberators were elec
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and ‘s’ in English text - may b
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content of rest of the signal spect
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cross the head, in opposite directi
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18.2 J. Sterne: The Audible Past (D
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18.71 T. Sporer: Creating, assessin
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786 Part F Biological and Medical A
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Medical 21. Medical Acous Acoustics
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21.1 Introduction to Medical Acoust
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Auscultation location Right & left
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portance. The Strouhal number has b
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Fig. 21.3 Phono-cardiograph transdu
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Amplitude 8 6 4 2 0 -2 -4 -6 Displa
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λ1 = c1 / fus θ1 λ2 = c2 / fus
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lood flow can be resolved if the si
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vided in the image thickness direct
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not as predicted, because the wave
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Fig. 21.18a,b Quadrature Doppler de
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a) b) c) 100 0 V mV 10 0 a = 13 a =
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Ultrasound contact gel Position enc
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a) 10 cm b) c) 10 cm Fig. 21.32a-c
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a) Pin B Pin A Ultrasound line b) M
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Organ Patient Ultrasound transducer
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systems cannot tell the difference
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40 µm can be resolved. For a 10 kH
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a) b) c) d) Medical Acoustics 21.4
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Fig. 21.54 Doppler spectral wavefor
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10 20 30 10 20 30 Pre-exercise B-mo
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Vibrations in a punctured artery De
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the veins and diffuse into the inte
Page 884 and 885:
21.5.3 Agitated Saline and Patent F
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transported by those cells and/or r
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1 0.8 0.6 0.4 0.2 0 Relative power
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High intensity focused ultrasound h
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a) b) c) Fig. 21.74a-c B-mode imagi
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provided simple metrics for the lik
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thickness of the carotid arteries,
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Structural 22. Structural Acoustics
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Structural Acoustics and Vibrations
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Magnitude (arb. units) 1.4 1.2 1.0
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This does not include the case wher
Page 906 and 907:
the mass matrix is taken to be cons
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Magnitude (dB) -10 -30 -50 0 1 2 3
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where D(ω) = ω 4 − 2iω 3�
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form y(x, t) = � Φn(x)qn(t) . (2
Page 914 and 915:
first to solve the wave equation (2
Page 916 and 917: 5 3 1 -1 -3 -5 0 1 2 3 4 5 6 7 8 9
Page 918 and 919: conditions at each end) are necessa
Page 920 and 921: from which we can derive through (2
Page 922 and 923: In this case, the eigenfrequencies
Page 924 and 925: of radiation modes and their link w
Page 926 and 927: Finally, the displacement is ˜ξ(x
Page 928 and 929: notes the value of this eigenmode a
Page 930 and 931: Pm = ˙Q H [Rs + Ra] ˙Q , (22.262)
Page 932 and 933: where and Ra = 2ζaω0 M Z(s) = zL
Page 934 and 935: Radiated Power. The mean acoustic p
Page 936 and 937: (22.318) can be written ξ(x, y, t)
Page 938 and 939: Denoting the eigenfrequencies and e
Page 940 and 941: Magnitude (arb. units) 3 2 1 0 -1 -
Page 942 and 943: for any real symmetric tensor Xij.
Page 944 and 945: F(N) 1 0.5 0 -0.5 -1 -1 -0.8 -0.6 -
Page 946 and 947: whose solution is θ1 = A cos ωτ.
Page 948 and 949: 4.5 3.5 2.5 1.5 A 0.5 0 0.5 1.0 1.5
Page 950 and 951: Equations (22.423) are usually writ
Page 952 and 953: 3. As the amplitude reaches the top
Page 954 and 955: Shallow Spherical Shells and Plates
Page 956 and 957: 22.20 L. Cremer, M. Heckl: Structur
Page 958 and 959: Noise Noise is discussed in terms o
Page 960 and 961: where the overbars represent time a
Page 962 and 963: Typical outdoor setting A-weighted
Page 964 and 965: 90 dB(A)” is widely used, and imp
Page 968 and 969: When each segment of the measuremen
Page 970 and 971: found from � LW = Lp + 10 log A +
Page 972 and 973: surement method is the ultimate use
Page 974 and 975: An intensity analyzer is more compl
Page 976 and 977: 23.2.5 Criteria for Noise Emissions
Page 978 and 979: Table 23.5 Table of limit values fr
Page 980 and 981: a) Air flows freely to rotor Weak t
Page 982 and 983: Static efficiency normalized to its
Page 984 and 985: ful applications. Good results are
Page 986 and 987: Table 23.8 Crossover speeds for var
Page 988 and 989: Reduction of airplane engine noise
Page 990 and 991: A variety of materials are used to
Page 992 and 993: ∆LF (dB) 0 -10 -20 α -30 0.05 0.
Page 994 and 995: Absorption coefficient 1.0 0.8 0.6
Page 996 and 997: high enough that there is little so
Page 998 and 999: 23.4.4 Criteria for Noise Immission
Page 1000 and 1001: Table 23.10 (cont.) Some features o
Page 1002 and 1003: Noise 23.4 Noise and the Receiver 1
Page 1004 and 1005: view of administrative procedures r
Page 1006 and 1007: provides recommendations for a foll
Page 1008 and 1009: sound power levels of noise sources
Page 1010 and 1011: 23.68 ISO: ISO 9296:1988 Acoustics
Page 1012 and 1013: in impedance tubes - Part 2: Transf
Page 1014 and 1015: 23.194 Commission of the European C
Page 1016 and 1017:
1022 Part H Engineering Acoustics P
Page 1018 and 1019:
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Page 1024 and 1025:
Page 1026 and 1027:
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Page 1044 and 1045:
Page 1046 and 1047:
Sound 25. Intens Sound Intensity So
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Under such conditions the intensity
Page 1050 and 1051:
a) Pressure and particle velocity 0
Page 1052 and 1053:
τ is a dummy time variable. The ca
Page 1054 and 1055:
Error in intensity (dB) 5 0 -5 -10
Page 1056 and 1057:
8 7 6 5 4 3 2 1 0 -1 -2 -3 Error du
Page 1058 and 1059:
crophones are calibrated with a pis
Page 1060 and 1061:
Sound power level (dB re 1 pW) 72 7
Page 1062 and 1063:
it is relatively straightforward si
Page 1064 and 1065:
intensity normal to the source. Thi
Page 1066 and 1067:
25.9 W. Maysenhölder: The reactive
Page 1068 and 1069:
25.77 ISO: ISO 11205 Acoustics - No
Page 1070 and 1071:
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Optical 27. Optical Methods Metho f
Page 1094 and 1095:
course also present in ordinary hol
Page 1096 and 1097:
Optical Methods for Acoustics and V
Page 1098 and 1099:
Page 1100 and 1101:
Page 1102 and 1103:
50 100 150 200 250 300 350 400 450
Page 1104 and 1105:
a) b) Optical Methods for Acoustics
Page 1106 and 1107:
nm 1000 0 -1000 150 y (mm) 100 50 O
Page 1108 and 1109:
Page 1110 and 1111:
Page 1112 and 1113:
Laser Optical Methods for Acoustics
Page 1114 and 1115:
References 27.1 E.F.F. Chladni: Die
Page 1116 and 1117:
27.75 E.-L.Johansson, L. Benckert,
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Page 1122 and 1123:
Page 1124 and 1125:
Page 1126 and 1127:
Page 1128 and 1129:
Page 1130 and 1131:
About the Authors Iskander Akhatov
Page 1132 and 1133:
Neville H. Fletcher Chapter F.19 Au
Page 1134 and 1135:
Brian C. J. Moore Chapter D.13 Univ
Page 1136 and 1137:
Detailed Contents List of Abbreviat
Page 1138 and 1139:
3.8.3 Acoustic Power ..............
Page 1140 and 1141:
4.8.3 Typical Speed of Sound Profil
Page 1142 and 1143:
7.3 Engines .......................
Page 1144 and 1145:
10 Concert Hall Acoustics Based on
Page 1146 and 1147:
13.4 Temporal Processing in the Aud
Page 1148 and 1149:
15.2.5 String-Bridge-Body Coupling
Page 1150 and 1151:
19.6 Birds ........................
Page 1152 and 1153:
22.4.5 Combinations of Elementary S
Page 1154 and 1155:
24.8 Overall View on Microphone Cal
Page 1156 and 1157:
Subject Index 3 dB bandwidth 463 A
Page 1158 and 1159:
British Medical Ultrasound Society
Page 1160 and 1161:
electric circuit analogues - acoust
Page 1162 and 1163:
hyperspeech 703 hypospeech 703 I IA
Page 1164 and 1165:
- participation factors 909 - stiff
Page 1166 and 1167:
- musical instruments 541 - musical
Page 1168 and 1169:
- nonlinear vibrations 957 - plate
Page 1170 and 1171:
subjective preference theory 353 su
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