Volume 137, Issue 6, June 2015
- jasa express letters
- acoustical oceanography
- animal bioacoustics
- architectural acoustics
- biomedical acoustics
- engineering acoustics
- musical acoustics
- physical acoustics
- psychological and physiological acoustics
- signal processing in acoustics
- speech communication
- structural acoustics and vibration
- underwater acoustics
- letters to the editor
- reviews of acoustical patents
Index of content:
- JASA EXPRESS LETTERS
Beamforming with a volumetric array of massless laser spark sources—Application in reflection tracking137(2015); http://dx.doi.org/10.1121/1.4920970View Description Hide Description
A volumetric array of laser-induced air breakdown sparks is used to produce a directional and steerable acoustic source. The laser breakdown array element is broadband, point-like, and massless. It produces an impulse-like waveform in midair, thus generating accurate spatio-temporal information for acoustic beamforming. A laser-spark scanning setup and the concept of a massless steerable source are presented and evaluated with a cubic array by using an off-line far field delay-and-sum beamforming method. This virtual acoustic array with minimal source influence can, for instance, produce narrow transmission beams to obtain localized and directional impulse response information by reflection tracking.
Repulsion of dispersion curves of quasidipole modes of anisotropic waveguides studied by finite element method137(2015); http://dx.doi.org/10.1121/1.4920969View Description Hide Description
In this letter repulsion of phase-velocity dispersion curves of quasidipole eigenmodes of waveguides with non-circular cross section in non-axisymmetric anisotropic medium is studied by the semi-analytical finite element technique. Borehole waveguide is used as an example. The modeling helps in clarifying the nature of this phenomenon, which is accompanied by the rotation of the orientation of two quasidipole modes with frequency and by the exchange of their behavior at near-crossover point. The dispersion curves cross only in the presence of exact symmetry. Such a scenario is the alternative to the stress-induced anisotropy crossing of dispersion curves.
Estimates of decision weights and internal noise in the masked discrimination of vowels by young and elderly adults137(2015); http://dx.doi.org/10.1121/1.4919701View Description Hide Description
Gilbertson and Lutfi [(2014). Hear. Res. 317, 9–14] report that older adults perform similarly to younger adults on a masked vowel discrimination task when the fundamental frequency (F0) of target and masker vowel differ but that the older adults perform more poorly when the F0 is the same. This paper presents an alternative analysis of those data to support the conclusion that the poorer performance of older adults is due to an increase in the decision weight on masker reflecting poorer selective attention in noise of older adults.
137(2015); http://dx.doi.org/10.1121/1.4914945View Description Hide Description
Physiological measures of neural activity in the auditory cortex have revealed plasticity following unilateral deafness. Central projections from the remaining ear reorganize to produce a stronger cortical response than normal. However, little is known about the perceptual consequences of this increase. One possibility is improved sound intensity discrimination. Intensity difference limens were measured in 11 individuals with unilateral deafness that were previously shown to exhibit increased cortical activity to sounds heard by the intact ear. Significantly smaller mean difference limens were observed compared with controls. These results provide evidence of the perceptual consequences of plasticity in humans following unilateral deafness.
137(2015); http://dx.doi.org/10.1121/1.4921340View Description Hide Description
Broadband cloaking and holography are achieved by creating an exact boundary condition on a surface enclosing an object or free space. A time-recursive, discrete version of the Kirchhoff–Helmholtz integral predicts the wavefield impinging on the surface, as well as its transmission through an arbitrary embedding or replacement medium. Surface source distributions proportional to the predicted wavefield cancel the incident waves and radiate the desired response. The fields inside and outside the surface can be controlled independently. A two-dimensional numerical example shows that cloaking and holography can be achieved to within numerical precision across the frequency range of the incident radiation.
137(2015); http://dx.doi.org/10.1121/1.4921447View Description Hide Description
A ballistic model-based method, which builds upon previous work by Lo and Ferguson [J. Acoust. Soc. Am. 132, 2997–3017 (2012)], is described for ranging small arms fire using a single acoustic sensor node collocated with the target, without a priori knowledge of the muzzle speed and ballistic constant of the bullet except that they belong to a known two-dimensional parameter space. The method requires measurements of the differential time of arrival and differential angle of arrival of the muzzle blast and ballistic shock wave at the sensor node. Its performance is evaluated using both simulated and real data.
137(2015); http://dx.doi.org/10.1121/1.4921673View Description Hide Description
Mapping vessel noise is emerging as one method of identifying areas where sound exposure due to shipping noise could have negative impacts on aquatic ecosystems. The probability distribution function (pdf) of sound exposure levels (SEL) is an important metric for identifying areas of concern. In this paper a probabilistic shipping SEL modeling method is described to obtain the pdf of SEL using the sonar equation and statistical relations linking the pdfs of ship traffic density, source levels, and transmission losses to their products and sums.
137(2015); http://dx.doi.org/10.1121/1.4921681View Description Hide Description
The aim of this study is to show the evidence of Mach stem formation for very weak shock waves with acoustic Mach numbers on the order of 10−3 to 10−2. Two representative cases are considered: reflection of shock pulses from a rigid surface and focusing of nonlinear acoustic beams. Reflection experiments are performed in air using spark-generated shock pulses. Shock fronts are visualized using a schlieren system. Both regular and irregular types of reflection are observed. Numerical simulations are performed to demonstrate the Mach stem formation in the focal region of periodic and pulsed nonlinear beams in water.
137(2015); http://dx.doi.org/10.1121/1.4921672View Description Hide Description
When signals are recorded on a planar aperture with point emitters/detectors, from either a three-dimensional (3D) scattering potential or from a 3D spatially-incoherent source distribution, an integral equation arises containing the product of two Green's functions in the weak scattering limit (the Born approximation). This fundamental imaging equation for scatterers or sources is derived and solved analytically.
137(2015); http://dx.doi.org/10.1121/1.4921674View Description Hide Description
Streaming services seek to optimise their use of bandwidth across audio and visual channels to maximise the quality of experience for users. This letter evaluates whether objective quality metrics can predict the audio quality for music encoded at low bitrates by comparing objective predictions with results from listener tests. Three objective metrics were benchmarked: PEAQ, POLQA, and VISQOLAudio. The results demonstrate objective metrics designed for speech quality assessment have a strong potential for quality assessment of low bitrate audio codecs.
137(2015); http://dx.doi.org/10.1121/1.4921728View Description Hide Description
Wormlike micellar fluids, being viscoelastic, support shear waves. Shear waves in 500 mM CTAB-NaSal micellar fluid were visualized by seeding the fluid with 212–250 μm diameter polyethylene microspheres. This method was compared to visualization through birefringence induced by shear stress in the fluid. Measured shear wave speeds were 733 and 722 mm/s, respectively, for each technique. Particle displacement was a sinusoidal function of time and displacement amplitude decreased quadratically with distance from the source. This supports the possibility of using particle amplitude measurements as a measure of attenuation even at low fluid concentration where birefringence visualization techniques fail.
137(2015); http://dx.doi.org/10.1121/1.4921678View Description Hide Description
This work presents a method to control the perceived distance of an auditory object by changing the directivity pattern of a loudspeaker and consequently the direct-to-reverberant ratio at the listening spot. Control of the directivity pattern is achieved by beamforming using a compact multi-driver loudspeaker unit. A small-sized cubic array consisting of six drivers is assembled, and per driver beamforming filters are derived from directional measurements of the array. The proposed method is evaluated using formal listening tests. The results show that the perceived distance can be controlled effectively by directivity pattern modification.
Voice source characterization using pitch synchronous discrete cosine transform for speaker identification137(2015); http://dx.doi.org/10.1121/1.4921679View Description Hide Description
A characterization of the voice source (VS) signal by the pitch synchronous (PS) discrete cosine transform (DCT) is proposed. With the integrated linear prediction residual (ILPR) as the VS estimate, the PS DCT of the ILPR is evaluated as a feature vector for speaker identification (SID). On TIMIT and YOHO databases, using a Gaussian mixture model (GMM)-based classifier, it performs on par with existing VS-based features. On the NIST 2003 database, fusion with a GMM-based classifier using MFCC features improves the identification accuracy by 12% in absolute terms, proving that the proposed characterization has good promise as a feature for SID studies.
Acoustic attenuation coefficients for polycrystalline materials containing crystallites of any symmetry class137(2015); http://dx.doi.org/10.1121/1.4921676View Description Hide Description
This letter provides a theoretical extension to the elastic properties of polycrystals in order to describe elastic wave scattering from grain boundaries. The extension allows the longitudinal and shear attenuation coefficients for scattering to be derived and is valid for polycrystals containing crystallites of any symmetry class. Attenuation curves are given for polycrystalline SiO2, ZrO2, and SnF2, which contain monoclinic crystallites. This work will allow ultrasonic techniques to be applied to new classes of materials containing nontrivial microstructures.
137(2015); http://dx.doi.org/10.1121/1.4921675View Description Hide Description
Time-domain prediction models have been developed for auditorium reflectors and room acoustic diffusers. The models are time-domain equivalents of the single-frequency formulations that exploit the Kirchhoff boundary conditions. Consequently, they are approximate, wave-based solutions to the Kirchhoff integral equation using surface meshes. The new time-domain formulations are validated by comparison to their frequency-domain equivalents for three different surfaces: a plane surface, a curved reflector, and a Schroeder diffuser. In terms of computation time and accuracy, the new models lie between the finite difference time domain and geometric room models.
137(2015); http://dx.doi.org/10.1121/1.4922011View Description Hide Description
The feasibility of using different voice coil transducers in applications with reciprocal transducers of mechanical waves is investigated. It was speculated that voice coil transducers could be a more efficient alternative to piezoelectric transducers in low frequency ranges. Five different voice coil transducers, originally constructed for either transmission or reception, were characterized in both modes of operation. A piezoelectric ceramic disk was used for comparison between the transducer types. The results show that voice coils indeed can function as reciprocal transducers and that the most sensitive of the evaluated transducers is more efficient than the piezoelectric disk for low frequencies.
137(2015); http://dx.doi.org/10.1121/1.4922012View Description Hide Description
Studies evaluating speech perception in noise have reported inconsistent results regarding a potential deficit in dyslexic children. So far, most of them investigated energetic masking. The present study evaluated situations inducing mostly informational masking, which reflects cognitive interference induced by the masker. Dyslexic children were asked to identify a female target syllable presented in quiet, babble, unmodulated, and modulated speech-shaped noise. Whereas their performance was comparable to normal-reading children in quiet, it dropped significantly in all noisy conditions compared to age-, but not reading level-matched controls. Interestingly, noise affected similarly the reception of voicing, place, and manner of articulation in dyslexic and normal-reading children.
137(2015); http://dx.doi.org/10.1121/1.4921682View Description Hide Description
An adaptive muffler with a flexible internal structure is considered. Flexibility is achieved using controlled flow valves. The proposed adaptive muffler is able to adapt to changes in engine operating conditions. It consists of a Helmholtz resonator, expansion chamber, and quarter wavelength resonator. Different combinations of the control valves' states at different operating conditions define the main working principle. To control the valve's position, an active noise control approach was used. With the proposed muffler, the transmission loss can be increased by more than 10 dB in the selected frequency range.
- ACOUSTICAL OCEANOGRAPHY
Bayesian environmental inversion of airgun modal dispersion using a single hydrophone in the Chukchi Sea137(2015); http://dx.doi.org/10.1121/1.4921284View Description Hide Description
This paper presents estimated water-column and seabed parameters and uncertainties for a shallow-water site in the Chukchi Sea, Alaska, from trans-dimensional Bayesian inversion of the dispersion of water-column acoustic modes. Pulse waveforms were recorded at a single ocean-bottom hydrophone from a small, ship-towed airgun array during a seismic survey. A warping dispersion time-frequency analysis is used to extract relative mode arrival times as a function of frequency for source-receiver ranges of 3 and 4 km which are inverted for the water sound-speed profile (SSP) and subbottom geoacoustic properties. The SSP is modeled using an unknown number of sound-speed/depth nodes. The subbottom is modeled using an unknown number of homogeneous layers with unknown thickness, sound speed, and density, overlying a halfspace. A reversible-jump Markov-chain Monte Carlo algorithm samples the model parameterization in terms of the number of water-column nodes and subbottom interfaces that can be resolved by the data. The estimated SSP agrees well with a measured profile, and seafloor sound speed is consistent with an independent headwave arrival-time analysis. Environmental properties are required to model sound propagation in the Chukchi Sea for estimating sound exposure levels and environmental research associated with marine mammal localization.
- ANIMAL BIOACOUSTICS
137(2015); http://dx.doi.org/10.1121/1.4919304View Description Hide Description
Automatic classification of fin, sei, and blue whale frequency modulated downsweeps has been a challenging task for bioacousticians. These calls overlap in frequency range and have similar time durations. The traditional spectrogram methodology, the Short Time Fourier Transform, tends to be ineffective because of the large temporal ambiguities needed to achieve the necessary frequency resolution to study the fine time-frequency (TF) structures. Spectrograms generated with the Pseudo Wigner-Ville Distribution (PWVD) provide much higher simultaneous TF resolution compared with the traditional method. The PWVD allows bioacousticians to study the fine TF structures of the sound, such as the instantaneous frequency, instantaneous bandwidth, contour slope, etc. These features set the foundation of identifying sounds that are usually considered difficult to discriminate using the traditional method. Wigner-Ville distribution of the baleen whale downsweeps showed distinguishable characteristics; for example, the TF contour of fin and sei whales exhibited concave and convex shapes, which have never been reported in the literature. A Support Vector Machine classifier was trained and tested based on the parameters extracted from the PWVD.