Volume 106, Issue 6, December 1999
- acoustics research letters online
- acoustical news—usa
- acoustical news—international
- general linear acoustics 
- 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 
- acoustical measurements and instrumentation 
- acoustic signal processing 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- bioacoustics 
- letters to the editor
Index of content:
- ACOUSTICS RESEARCH LETTERS ONLINE
106(1999); http://dx.doi.org/10.1121/1.428147View Description Hide Description
Interferometric recordings of sound-evoked vibrations in the basal turn and hook regions of the guinea-pig cochlea are used to show that reflective microbeads (i) follow the motion of the structures on which they are placed, and (ii) do not affect this motion dramatically. Extrapolating these findings to other types of reflective or radioactive material lends support to the findings of numerous studies of cochlear mechanics.
Effect of acoustic dynamic range on phoneme recognition in quiet and noise by cochlear implant users106(1999); http://dx.doi.org/10.1121/1.428148View Description Hide Description
The present study measured phoneme recognition in cochlear implant users when the dynamic range of the input speech signals was reduced by either peak clipping or center clipping. In quiet, reducing the acoustic dynamic range to 30 dB still provides sufficient speechinformation for phoneme identification in cochlear implant users with 4-channel continuous interleaved sampler strategy and normal-hearing listeners listening to correspondingly degraded speech. Phoneme recognition decreased when the dynamic range was reduced below 30 dB: peak clipping was more detrimental to vowel recognition and center clipping was more detrimental to consonant recognition. However, in background noise, center clipping produced a small increase in speech recognition for cochlear implant listeners.
106(1999); http://dx.doi.org/10.1121/1.428150View Description Hide Description
Initial and medial consonants were recorded in three vowel contexts for use in speech recognition experiments. Five male and five female talkers were recorded producing the twenty-five consonants in medial (v/C/v) and initial (C/v) positions using vowels (“hod”), (“heed”), and (“who’d”). The sampling rate for these recordings was 44.1 kHz. Representative tokens of each consonant were amplitude normalized to the steady-state portion of the vowel. Listening tests were conducted with normal-hearing listeners on a subset of twenty consonants in all three vowel contexts and in initial and medial positions. The results showed that the consonants were clearly recognized with only a few minor confusions, primarily between and /ð/. The full set of recordings is available for research use.
106(1999); http://dx.doi.org/10.1121/1.428154View Description Hide Description
Two experiments compared auditory sensitivity in a group of 12 adult dyslexics and matched control listeners. The first experiment measured frequency discrimination and frequency modulation detection thresholds at both 1 and 6 kHz. Although thresholds were larger for the dyslexic group, the differences were not statistically reliable. The second experiment measured the binaural masking level difference for a 200 Hz pure tone in noise. Thresholds did not differ significantly between the two groups. The data provide little support for the hypothesis that dyslexic listeners are impaired in their ability to process information in the temporal fine structure of auditory stimuli.
106(1999); http://dx.doi.org/10.1121/1.428156View Description Hide Description
- GENERAL LINEAR ACOUSTICS 
106(1999); http://dx.doi.org/10.1121/1.428158View Description Hide Description
The paper deals with the reduction of the sound energy in the shadow region behind barriers by means of an attached body at the edge of the screen. The reflecting attributes of the barrier’s headpiece are described by a locally reacting impedance. Diffraction at ideal soft and hard bodies demonstrates the basic principle of tangential power transport parallel to their surface: the impedance must be chosen so that the tangential intensity near the edge is lowered, turning the incoming power in harmless directions. The differences due to finite impedances are then discussed. The physical principles are demonstrated in frozen pictures of the sound field for the different cases. Theoretical computations show considerably improved levels in the shadow zone for larger angles of diffraction. These are compared with empirical results, and practical applications are discussed.
106(1999); http://dx.doi.org/10.1121/1.428159View Description Hide Description
A quantitative ultrasonic imaging method employing time-domain scattering data is presented. This method provides tomographic images of medium properties such as the sound speed contrast; these images are equivalent to multiple-frequency filtered-backpropagation reconstructions using all frequencies within the bandwidth of the incident pulse employed. However, image synthesis is performed directly in the time domain using coherent combination of far-field scattered pressure waveforms, delayed and summed to numerically focus on the unknown medium. The time-domain method is more efficient than multiple-frequency diffraction tomography methods, and can, in some cases, be more efficient than single-frequency diffraction tomography. Example reconstructions, obtained using synthetic data for two- and three-dimensional scattering of wideband pulses, show that the time-domain reconstruction method provides image quality superior to single-frequency reconstructions for objects of size and contrast relevant to medical imaging problems such as ultrasonic mammography. The present method is closely related to existing synthetic-aperture imaging methods such as those employed in clinical ultrasound scanners. Thus, the new method can be extended to incorporate available image-enhancement techniques such as time-gain compensation to correct for medium absorption and aberration correction methods to reduce error associated with weak scattering approximations.
106(1999); http://dx.doi.org/10.1121/1.428160View Description Hide Description
A novel numerical analysis of acoustic diffraction by a rectangular screen is described. The boundary integral model of the system is solved by a Galerkin method using as a basis the scaling functions of discrete wavelet theory. The use of scaling functions enables the quadruple integrals in the Galerkin method to be analytically reduced to double integrals, and the singular and hypersingular integrals can be found from a recurrence formula. Numerical tests show that the new method is more efficient than a boundary element method based on collocation, particularly when the screen is irradiated near grazing incidence.
106(1999); http://dx.doi.org/10.1121/1.428161View Description Hide Description
Reflection and transmission spectra of a plane longitudinal wave normally incident on a periodic (square) array of identical spherical particles in a polyester matrix are measured at wavelengths which are comparable to the particle radius and the interparticle distance. The spectra are characterized by several resonances whose frequencies are close to the cutoff frequencies for the shear wave diffraction orders. Arrays of heavy particles (lead and steel) exhibit a pronounced resonance which occurs when the lattice resonant frequency is close to the frequency of the rigid-body translation (dipole) resonance of an isolated sphere in an unbounded matrix. An approximate low-frequency theory is developed which assumes that the inclusions are rigid, but which takes into account the multiple-scattering effect. The comparison between theory and the experiment is found to be good for arrays with particle area fraction as high as 32%.
106(1999); http://dx.doi.org/10.1121/1.428162View Description Hide Description
Ultrasonic attenuationmeasurements in unconsolidated sand with pore fluids ranging in viscosity between 0.001 and 1 Pa⋅s were compared with the predictions of fluid flow and scattering theories. Laboratory experiments were performed for P waves propagating through sand samples saturated with water, castor oil and two different silicone oils. The attenuation shows a frequency squared dependence for all measurements, regardless of viscosity, in the range between 100 and 1000 kHz. The results show that for unconsolidated sand, fluid flow models which imply significant effects of the viscous pore fluids on ultrasonic waves cannot explain the laboratory measurements. The main attenuationeffects observed in the laboratory can be simulated with a three-dimensional generalized dynamic composite elastic medium model, which includes scattering from the pores and grains as well as intrinsic attenuation caused by the viscous pore fluids. For the studied sand samples, scattering is the main attenuation mechanism for ultrasonicP waves.
Computation of transient radiation in semi-infinite regions based on exact nonreflecting boundary conditions and mixed time integration106(1999); http://dx.doi.org/10.1121/1.428163View Description Hide Description
Transient radiation in a semi-infinite region, bounded by a planar infinite baffle with a local acoustic source is considered. The numerical simulation of the transient radiation problem requires an artificial boundary here chosen to be a hemisphere, which separates the computational region from the surrounding unbounded acoustic medium. Inside the computational region we use a semidiscrete finite element method. On we apply the exact nonreflecting boundary condition (NRBC) first derived by Grote and Keller for the free-space problem. Since the problem is symmetric about the infinite planar surface, in order to satisfy the rigid baffle condition it is sufficient to restrict the indices in the spherical harmonic expansion which defines the NRBC and scale the radial harmonics which drive auxiliary equations on the boundary. The Fourier expansion in the circumferential angle appearing in the NRBC may be used to efficiently model axisymmetric problems in two dimensions. A new mixed explicit-implicit time integration method which retains the efficiency of explicit pressure field updates without the need for diagonal matrices in the auxiliary equations on is presented. Here, the interior finite elementequations are integrated explicitly in time while the auxiliary equations are integrated implicitly. The result is a very natural and highly efficient algorithm for large-scale wave propagation analysis. Numerical examples of fully transient radiation resulting from a piston transducer mounted in an infinite planar baffle are compared to analytical solutions to demonstrate the accuracy of the mixed time integration method with the NRBC for the half-space problem.
106(1999); http://dx.doi.org/10.1121/1.428164View Description Hide Description
The design of a wide frequency band neutralizer, vibration absorber and/or structural fuzzy, in the form of multiple-sprung masses, is extensively reported in the open literature. The action of the device is reported in terms of the joint point impedance of the sprung masses. This joint impedance is merely the sum over the impedances of the individual sprung masses at the common point to which the device is to be attached to a master structure. The normalized frequency bandwidth of a device composed of a single-sprung mass is proportional to the loss factor of that sprung mass. To increase this bandwidth, a device composed of more than one sprung mass, with distributed resonance frequencies, is utilized. To keep suppressed the undulations in the joint impedance of a set composed of a multiplicity of sprung masses, the loss factors are rendered larger than the normalized separations between adjacent antiresonance frequencies. This modal overlap condition, together with consideration of weight, are central to the design of the device. The analysis of the device is enriched by considering two distinct distributions of resonance frequencies for each set of sprung masses. Moreover, the ranges and parameters which specify that device are limited to reasonably moderate values; e.g., the useful frequency bandwidth of a given device is limited to one-third of its center frequency and the number of sprung masses in a device is restricted not to exceed one-score. In a set employing the first resonance frequency distribution, as the number of sprung masses is initially increased, an increase in the bandwidth is accompanied by an increase in the level of the joint impedance. As the number of sprung masses is further increased, the bandwidth and the level of the joint impedance become saturated. In a set incorporating the second resonance frequency distribution, an ongoing increase in the bandwidth, as the number of sprung masses increases, is accompanied by an ongoing decrease in the level of the joint impedance. The examination of these and other characteristics in the joint impedance of the sprung masses is provided by data obtained in computer experiments performed on a few selected sets of sprung masses.
106(1999); http://dx.doi.org/10.1121/1.428165View Description Hide Description
In a companion paper the characterization of a multiple-sprung masses design for wideband noise control is presented. The characterization is largely conducted in terms of the point impedance of a set of sprung masses. The sprung masses in the set are collectively acting at a point. In that companion paper the dependencies of the joint impedance on the number of sprung masses, the modal overlap factors, the total mass, and the resonance frequency distribution are of particular interest. In the present paper this characterization of a set of sprung masses is utilized to define a number of design criteria that determine the potential viability of the set as a noise control device. In the final analysis, the device must be assessed in an in situ setting. In that setting the device is tested in terms of the overall gain. The determination of the overall gain requires, in addition to the joint impedance of the device, the impedance of the hosting master structure at the point of attachment. (The device is meant to control the noise in the master structure.) It is argued that although the overall gain is the final judge, the potential viability of a device may be a useful critique of the intended performance of the device. In this vein, a viability and a criterion of promise are defined to assist with the design processes of this noise control device. In assessing the viability and in satisfying the criterion of promise, the desired characteristics in a set of sprung masses can be judicially selected.
106(1999); http://dx.doi.org/10.1121/1.428166View Description Hide Description
Problems in structural acoustics involving finite plates can be formulated using integral equation methods. The unknown function within the integral equation must satisfy the plate edge conditions, and hence appropriate expansion functions must be used. The expansion functions developed here are aimed at treating a wide class of problems. Once such functions are found, the solution process and numerical implementation are relatively straightforward. The speed of convergence to “exact” comparison solutions is fast even in the singular limit of high frequencies and wide plates. A set of expansion functions with the required properties is constructed and some illustrative problems are treated.
- NONLINEAR ACOUSTICS 
106(1999); http://dx.doi.org/10.1121/1.428167View Description Hide Description
Nonlinear propagation of finite-amplitude acoustic pulse in water and through a sample of water-saturated granular medium is considered. To generate high-intensity acoustic pulses laser generation of sound was used. The region of fluid perturbed by the laser acts as a volume-distributed source. In a fluid with weak light attenuation, a cylindrical source could be formed by a narrow laser beam. The nonlinear distortion of the cylindrical finite-amplitude wave in water is investigated. The measured rate of distortion corresponds to that calculated in the approximation of nonlinear acoustics. In a strongly light-absorbing medium, a wide (compared to the typical sound wavelength) laser beam produces a circular planar source. Such a source produces acoustical pulses of amplitude up to 3 MPa and duration about 1 μs in different fluids. This source was used to investigate the propagation of high-intensity wide frequency band sound signals in a sample of water-saturated cobalt–manganese crust (CMC). Specific acoustical features of the crust such as nonlinear sound pulse distortion and the frequency dependance of attenuation, varying with the amplitude, are considered. Theoretical interpretation of the results is given.
106(1999); http://dx.doi.org/10.1121/1.428168View Description Hide Description
The quasi one-dimensional problem of nonlinear longitudinal wave propagation in the elastic medium undergoing inhomogeneous plane prestrain is investigated theoretically. The analytical solution to describe the propagation of the wave with an arbitrary smooth initial profile is derived. The influence of the magnitude of the prestrain intensity on the distortion of the wave profile is studied. The sine-wave propagation in the medium subjected to the distributed static load is considered in more detail. The dependence of the sine-wave characteristics on the physical and geometrical properties of the medium and on the parameters of the predeformed state is clarified. The possibility to enhance the efficiency of ultrasonicnondestructive testing making use of the nonlinear effects of wave propagation is discussed. The algorithm to evaluation of the parameters of plane strain on the basis of wave profile evolution data is proposed.
106(1999); http://dx.doi.org/10.1121/1.428169View Description Hide Description
A solution for multifrequency plane waves propagating through a dissipative and nonlinear medium is presented. It originates from the well-known Bessel function series ratio for a pure sinusiodal wave, introduced by Cole and Mendousse. The solution is exact. The only limitation, inherited from the single-frequency solution, is the slow convergence of the series when the nonlinearity is very large compared to the dissipation. Otherwise any frequencies, amplitudes and phases can be introduced in the original wave and the solution is valid for any propagated distance.