Volume 126, Issue 3, September 2009
- jasa express letters
- letters to the editor
- nonlinear acoustics 
- aeroacoustics, atmospheric sound 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- transduction 
- structural acoustics and vibration 
- noise: its effects and control 
- architectural acoustics 
- acoustical measurements and instrumentation 
- acoustic signal processing 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- speech processing and communication systems 
- music and musical instruments 
- bioacoustics 
- acoustical news
- acoustical standards news
- book reviews
- reviews of acoustical patents
Index of content:
- JASA EXPRESS LETTERS
126(2009); http://dx.doi.org/10.1121/1.3182858View Description Hide Description
The theory of the acoustics of dilute bubbly liquids is reviewed, and the dispersion relation is modified by including the effect of liquid compressibility on the natural frequency of the bubbles. The modified theory is shown to more accurately predict the trend in measured attenuation of ultrasonicwaves. The model limitations associated with such high-frequency waves are discussed.
126(2009); http://dx.doi.org/10.1121/1.3186800View Description Hide Description
Existing ultrasonic manipulation devices capable of pushing particles to a surface (“quarter-wave” devices) have significant potential in sensor applications. A configuration for achieving this that uses the first thickness resonance of a layered structure with both a thin reflector layer and thin-fluid layer is described here. Crucially, this mode is efficient with lossy reflector materials such as polymers, produces a more uniform acoustic radiation force at the reflector, and is less sensitive to geometric variations than previously described quarter-wave devices. This design is thus expected to be suitable for mass produced, disposable devices.
126(2009); http://dx.doi.org/10.1121/1.3186798View Description Hide Description
Because horseshoe bats emit a long-duration pulse, the returning echo temporally overlaps with the emitted pulse during echolocation. Here, the pulse-echo interaction that horseshoe bats actually experience during flight was examined using onboard telemetrysound recordings. Doppler-shifted returning echoes produced beats in the amplitude patterns of constant-frequency components. Bats shortened the pulse duration with target distance, but the overlap duration was at least 8 ms within the approach phase. The computations suggest that the phase difference in slowly amplitude-modulated sound (the beat signal) provides a useful cue for target localization.
126(2009); http://dx.doi.org/10.1121/1.3182859View Description Hide Description
The accuracy of modal frequency and damping estimators for non-lightly damped single degree of freedom systems depend on the response parameter used as well as the damping mechanism. Therefore, in order to make accurate modal parameter measurements, the damping mechanism at play must be known to be either viscous or hysteretic a priori. Here, comparisons between the evaluated frequency values are used to glean this information. The damping mechanism of an experimental system (consisting of resilient layer and mass plate) is then determined using two simple modal parameter estimators and applying statistical methods.
Experimental investigation on pore size effect on the linear viscoelastic properties of acoustic foams126(2009); http://dx.doi.org/10.1121/1.3186799View Description Hide Description
This paper presents linear viscoelasticmeasurement on a large frequency range () for cross-linked polymer open-cell foams of same density and different pore sizes. This large extension of frequency range is obtained by the validation of a frequency-temperature superposition principle, commonly used with polymers. At higher frequencies, the shear moduli are independent of the pore size. In acoustical insulation range (1 Hz–16 kHz), the shear moduli decreases with the foams’ pore size.
126(2009); http://dx.doi.org/10.1121/1.3204155View Description Hide Description
A difference of approximately exists between the level of spoken English determined using the ANSI standard vu-meter method compared to the common root-mean-square (rms) method. If the rms method is substituted for the present ANSI standard method for calibrating a speechaudiometer, for example, the reported speech reception thresholds will improve : Speech levels read approximately less using rms. Similarly, the reported signal-to-noise ratio required to understand speech in a speech-spectrum noise will be better using rms. A simple method for obtaining a close approximation to traditional calibrations using a modified rms method is given.
126(2009); http://dx.doi.org/10.1121/1.3204765View Description Hide Description
This paper proposes an efficient method to improve speaker recognition performance by dynamically controlling the ratio of phoneme class information. It utilizes the fact that each phoneme contains different amounts of speaker discriminative information that can be measured by mutual information. After classifying phonemes into five classes, the optimal ratio of each class in both training and testing processes is adjusted using a non-linear optimization technique, i.e., the Nelder–Mead method. Speaker identification results verify that the proposed method achieves 18% improvement in terms of error rate compared to a baseline system.
- LETTERS TO THE EDITOR
126(2009); http://dx.doi.org/10.1121/1.3192348View Description Hide Description
Temporal weights used by listeners when judging the overall loudness of a stimulus were measured for a -long noise centered around , whose level was randomly perturbed every . The bandwidth was either (broadband condition) or (narrowband condition). The first contributed significantly more than later segments to overall loudness perception in the broadband condition. The effect was significantly reduced in the narrowband condition which is in line with the hypothesis that a greater spectralloudness summation at stimulus onset might be the mechanism behind the onset accentuation.
Spectral modulation detection and vowel and consonant identifications in cochlear implant listenersa)126(2009); http://dx.doi.org/10.1121/1.3179670View Description Hide Description
Speech understanding by cochlear implant listeners may be limited by their ability to perceive complex spectral envelopes. Here, spectral envelope perception was characterized by spectralmodulation transfer functions in which modulation detection thresholds became poorer with increasing spectral modulation frequency (SMF). Thresholds at low SMFs, less likely to be influenced by spectral resolution, were correlated with vowel and consonant identifications [Litvak, L. M. et al. (2008). J. Acoust. Soc. Am.122, 982–991] for the same listeners; while thresholds at higher SMFs, more likely to be affected by spectral resolution, were not. Results indicate that the perception of broadly spaced spectral features is important for speech perception.
47-channel burst-mode recording hydrophone system enabling measurements of the dynamic echolocation behavior of free-swimming dolphins126(2009); http://dx.doi.org/10.1121/1.3184536View Description Hide Description
Detailed echolocation behavior studies on free-swimming dolphins require a measurement system that incorporates multiple hydrophones (often ). However, the high data flow rate of previous systems has limited their usefulness since only minute long recordings have been manageable. To address this problem, this report describes a 47-channel burst-mode recording hydrophone system that enables highly resolved full beamwidth measurements on multiple free-swimming dolphins during prolonged recording periods. The system facilitates a wide range of biosonar studies since it eliminates the need to restrict the movement of animals in order to study the fine details of their sonar beams.
- NONLINEAR ACOUSTICS 
Quantification of material nonlinearity in relation to microdamage density using nonlinear reverberation spectroscopy: Experimental and theoretical study126(2009); http://dx.doi.org/10.1121/1.3184583View Description Hide Description
High amplitude vibrations induce amplitude dependence of the characteristicresonance parameters (i.e., resonance frequency and damping factor) in materials with microscopic damage features as a result of the nonlinear constitutive relation at the damage location. This paper displays and quantifies results of the nonlinear resonance technique, both in time (signal reverberation) and in frequency (sweep) domains, as a function of sample crack density. The reverberation spectroscopy technique is applied to carbon fiber reinforced plastic (CFRP) composites exposed to increasing thermal loading. Considerable gain in sensitivity and consistent interpretation of the results for nonlinear signatures in comparison with the linear characteristics are obtained. The amount of induced damage is quantified by analyzing light optical microscopy images of several cross-sections of the CFRP samples using histogram equalization and grayscale thresholding. The obtained measure of crack density is compared to the global macroscopic nonlinearity of the sample and explicitly confirms that the increase in nonlinearity is linked to an increased network of cracks. A change from 1% to 3% in crack density corresponds to a tenfold increase in the signature of nonlinearity. Numerical simulations based on a uniform distribution of a hysteretic nonlinear constitutive relation within the sample support the results.
Influence of the bubble-bubble interaction on destruction of encapsulated microbubbles under ultrasound126(2009); http://dx.doi.org/10.1121/1.3179677View Description Hide Description
Influence of the bubble-bubble interaction on the pulsation of encapsulated microbubbles has been studied by numerical simulations under the condition of the experiment reported by Chang et al. [IEEE Trans. Ultrason Ferroelectr. Freq. Control48, 161 (2001)]. It has been shown that the natural (resonance) frequency of a microbubble decreases considerably as the microbubble concentration increases to relatively high concentrations. At some concentration, the natural frequency may coincide with the driving frequency. Microbubble pulsation becomes milder as the microbubble concentration increases except at around the resonance condition due to the stronger bubble-bubble interaction. This may be one of the reasons why the threshold of acoustic pressure for destruction of an encapsulated microbubble increases as the microbubble concentration increases. A theoretical model for destruction has been proposed.
A generalized statistical Burgers equation to predict the evolution of the power spectral density of high-intensity noise in atmosphere126(2009); http://dx.doi.org/10.1121/1.3167393View Description Hide Description
The present work is a theoretical/numerical investigation of the combined effect of nonlinearity, geometrical spreading, and atmospheric absorption on the evolution of the power spectral density of a noise field, when only the power spectral density is known at source, not the signal itself. This is often the case in aircraft noise measurements. The method presented here is based on and extends previous work [P. Menounou and D. T. Blackstock, J. Acoust. Soc. Am.115, 567–580 (2004)], where a recursion equation [statistical Burgers equation (SBE)] describing the evolution of the joint moments of the noise source was derived. The SBE is restricted to plane waves, thermoviscous fluids, and short propagation distances (preshock region). In the present work, the SBE is extended to include the effects of geometrical spreading and arbitrary absorption, in order to be applicable to propagation of high-intensity noise through atmosphere. A new equation is derived and termed generalized SBE, and a method for its numerical implementation is presented. Results are in good agreement with time domain calculations for propagation in atmosphere of (i) sinusoidal signals (benchmark case) and (ii) Gaussian processes with known power spectral densities at source.
- AEROACOUSTICS, ATMOSPHERIC SOUND 
126(2009); http://dx.doi.org/10.1121/1.3177263View Description Hide Description
For scattering of plane waves at a sudden area expansion in a duct, the presence of flow may significantly alter the reactive properties. This paper studies the influence of a mean flow field and unstable separated flow on the reactive properties of the expansion, formulated as an end correction. Theoretical and experimental results show that the expansion end correction is significantly affected by the flow and hydrodynamic waves excited at the edge of the expansion. The effects are different in three regions where the Strouhal number is small, of order 1, and large. The influence is most significant at Strouhal numbers of the order 1, with specific limiting values for large and small Strouhal numbers, respectively. In the analytic model, an important feature is the shear layer at the edge modeled as a vortex sheet with the unsteady Kutta condition applied at the edge. The influence of Mach number, Helmholtz number, and area expansion ratio is studied, and a quasistationary, small Strouhal number, approximation yields an expression for the end correction. Further, the influence of edge condition is explored, emphasizing the importance of interaction between sound and unsteady vorticity shedding at the edge of the area expansion.
126(2009); http://dx.doi.org/10.1121/1.3192332View Description Hide Description
The soundgenerated by a vortex moving across a duct section lined with porous materials and the corresponding vortex dynamics are studied numerically in the present investigation. The combined effects of the effective fluid density, the flow resistance, the length, and the thickness of the porous linings on the vortex dynamics and sound generation are examined in detail. Results show that stronger sound radiation will take place when the length and the thickness of the porous linings are increased or when the effective fluid density is reduced. The flow resistance can only result in stronger sound radiation within a range whose width depends on the abovementioned system parameters. Such sound amplification cannot be achieved when the initial vortex height gets closer and closer to the duct centerline. The present results also indicate the strong correlation between vortex acceleration and the sound radiation under the actions of the porous linings.
126(2009); http://dx.doi.org/10.1121/1.3192221View Description Hide Description
To calculate the noise emanating from a turbulent flow using an acoustic analogy knowledge concerning the unsteady characteristics of the turbulence is required. Specifically, the form of the turbulent correlation tensor together with various time and length-scales are needed. However, if a Reynolds Averaged Navier–Stores calculation is used as the starting point then one can only obtain steady characteristics of the flow and it is necessary to model the unsteady behavior in some way. While there has been considerable attention given to the correct way to model the form of the correlation tensor less attention has been given to the underlying physics that dictate the proper choice of time-scale. In this paper the authors recognize that there are several time dependent processes occurring within a turbulent flow and propose a new way of obtaining the time-scale. Isothermal single-stream flow jets with Mach numbers 0.75 and 0.90 have been chosen for the present study. The Mani–Gliebe–Balsa–Khavaran method has been used for prediction of noise at different angles, and there is good agreement between the noise predictions and observations. Furthermore, the new time-scale has an inherent frequency dependency that arises naturally from the underlying physics, thus avoiding supplementary mathematical enhancements needed in previous modeling.
- UNDERWATER SOUND 
Statistics of normal mode amplitudes in an ocean with random sound-speed perturbations: Cross-mode coherence and mean intensity126(2009); http://dx.doi.org/10.1121/1.3158818View Description Hide Description
In this paper Creamer’s [(Year: 1996). J. Acoust. Soc. Am.99, 2825–2838] transport equation for the mode amplitude coherence matrix resulting from coupled mode propagation through random fields of internal waves is examined in more detail. It is shown that the mode energy equations are approximately independent of the cross mode coherences, and that cross mode coherences and mode energy can evolve over very similar range scales. The decay of cross mode coherence depends on the relative mode phase randomization caused by coupling and adiabatic effects, each of which can be quantified by the theory. This behavior has a dramatic effect on the acoustic field second moments like mean intensity. Comparing estimates of the coherence matrix and mean intensity from Monte Carlo simulation, and the transport equations, good agreement is demonstrated for a deep-water example.
126(2009); http://dx.doi.org/10.1121/1.3180698View Description Hide Description
A method is presented to examine the problem of simulating the beam time series response for an array of arbitrary shape in a range-dependent environment using a combination of parabolic equation (PE) forward modeling and local normal modeanalysis. The procedure involves computing the acoustic pressure field as a function of depth, using the PE, at the nominal center location of the array. The field is then decomposed into local complex normal mode amplitudes. These mode amplitudes are used to compute the field response on each array element, via range-independent normal mode theory. Conventional plane-wave beamforming is then applied. It is shown that a single matrix computation can be used to map the field as a function of depth to the beam response as a function of angle. The method is applied to two broadband range-independent examples to demonstrate its accuracy. It is then applied to a shallow-water range-dependent experiment from off the Florida coast and a deep-water range-dependent experiment from sound scattering off a seamount in the open ocean. For both range-dependent examples, the model simulation results reproduce the qualitative features observed in the data.
126(2009); http://dx.doi.org/10.1121/1.3180696View Description Hide Description
Sound scattering by solid particles suspended in a turbulent jet is investigated. Measurements of the scattered amplitude were made in a bistatic geometry at frequencies between 1.5 and , and at scattering angles from 95° to 165° relative to the forward direction. Two types of particle were used: nearly spherical lead-glass beads and aspherical natural sand grains. For each particle type, experiments were carried out using and median diameter grain sizes, corresponding to . The sphericity of the sand grains, defined as the ratio of projected perimeter size to projected area size, was 1.08. The lead-glass bead results are consistent with an elastic sphere model. A rigid movable sphere model provides the best fit to the sand data, and the best-fit diameter is within 4% of the equivalent volume size. However, the scattering pattern for sand is systematically smoother than predicted: that is, the undulations in the angular scattering pattern predicted by spherical scatterertheory are present, but muted. This observed departure from spherical scatterertheory is attributed to disruption of the interference among creeping waves by the irregular surfaces of natural sand grains.
High resolution population density imaging of random scatterers with the matched filtered scattered field variance126(2009); http://dx.doi.org/10.1121/1.3177271View Description Hide Description
The matched filter enables imaging with high spatial resolution and high signal-to-noise ratio by coherent correlation with the expected field from what is assumed to be a discrete scatterer. In many physical imaging systems, however, returns from a large number of randomized scatterers, ranging from thousands to millions of individuals, are received together and the coherent or expected field vanishes. Despite this, it is shown that cross-spectral coherence in the matched filtered variance retains a pulse compression property that enables high-resolution imaging of scatterer population density. Analytic expressions for the statistical moments of the broadband matched filtered scattered field are derived in terms of the medium’s Green’s function, object scatter function, and spatial distribution using a single-scatter approximation. The formulation can account for potential dispersion in the medium and target over the signal bandwidth, and can be used to compare the relative levels of the coherent and incoherent scattered intensities. The analytic model is applied to investigate population density imaging of fish distributions in the Gulf of Maine with an ultrasonic echosounder. The results are verified with numerical Monte-Carlo simulations that include multiple scattering, illustrating that the single-scatter approximation is valid even for relatively dense Atlantic herring (Clupea harengus) schools.