Directional Response Pattern Research Articles

Interpretation of dynamic response of a very complex landslide (Latian-Tehran) based on ambient noise investigation

Single station ambient noise measurements were performed in 122 points on a complex landslide at the left bank of Latian Dam reservoir in the north-east of Tehran (Iran), to investigate the seismic site response of a landslide, especially the nature and causative factor of directional site amplification. Recorded data were analyzed through the horizontal to vertical spectral ratio technique to obtain the resonance frequencies (f0), spectral ratio amplitude (A) and orientation and intensity of directional response over sliding and surrounding area. The results have a great coherence to geotechnical and geological investigation result and are tightly related to the landslide structure in such a way that outside the sliding area there is no or negligible sign of directional response. In general the result revealed two range of frequencies with high amplitude and directivity over the landslide mass; the first one around 1.2Hz, ubiquitous, that seems to be related to normal mode vibration of the entire unstable mass, named as underlying layer in this paper. The second one at higher frequencies that is spatially variable over the landslide, which seems to be related to the effect of local surficial features (such as local sharp curvatures and ridges or blocks detached by tension fractures). Directional response pattern of both the underlying layer and surficial features is controlled by 2D or 3D features causing higher amplitude in the most kinematically free direction. It seems that the seismic response of the underlying layer at the surface is modified by directional filtering of the overlying superficial layer. This modification effects tightly related to the transfer function of surficial features especially their cross-coupling terms. Based on this study, a general rule is proposed to declare conditions which are essential to induce severe directional response at a specific site.

Analyzer allows testing of polar response patterns of directional hearing aids

Analyzer allows testing of polar response patterns of directional hearing aids

Specific features of estimation of levels and spatial spectrum of ocean noise by a single multicomponent combined receiver

Algorithms for estimation of the spatial spectrum of ocean noise using a single hydroacoustic combined receiving module (CRM), which records the field of acoustic pressure and its gradient projections onto three mutually orthogonal spatial directions for small wave sizes, are discussed. It is shown that in spite of a rather “obtuse” cosine directional response pattern of vector channels of this receiving module it is possible to obtain good determination of the direction toward the local source due to recording the vector characteristic of the acoustic field (acoustic power flux), and in the absence of powerful local sources in the water area the spatial spectrum of noise close to a realistic one can be obtained.

Physiological evidence for binaural directional computations in the brainstem of the oyster toadfish, Opsanus tau (L.).

Comparisons of left and right auditory input are required for sound source localization in most terrestrial vertebrates. Previous physiological and neuroanatomical studies have indicated that binaural convergence is present in the ascending auditory system of the toadfish. In this study, we introduce a new technique, otolith tipping, to reversibly alter directional auditory input to the central nervous system of a fish. The normal directional response pattern (DRP) was recorded extracellularly for auditory cells in the first-order descending octaval nucleus (DON) or the midbrain torus semicircularis (TS) using particle motion stimuli in the horizontal and mid-sagittal planes. The same stimuli were used during tipping of the saccular otolith to evaluate changes in the DRPs. Post-tipping DRPs were generated and compared with the pre-tipping DRPs to ensure that the data had been collected consistently from the same unit. In the DON, ipsilateral or contralateral tipping most often eliminated spike activity, but changes in spike rate (+/-) and DRP shape were also documented. In the TS, tipping most often caused a change in spike rate (+/-) and altered the shape or best axis of the DRP. The data indicate that there are complex interactions of excitatory and inhibitory inputs in the DON and TS resulting from the convergence of binaural inputs. As in anurans, but unlike other terrestrial vertebrates, binaural processing associated with encoding the direction of a sound source begins in the first-order auditory nucleus of this teleost.

Evidence of binaural directional computations in the auditory pathway of a teleost fish.

Although binaural processing is known to be critical for sound source localization in terrestrial vertebrates, binaural processing for sound source localization in fishes has not been demonstrated. Previous physiological and neuroanatomical studies have indicated that interaural convergence is present in auditory pathway of oyster toadfish (Opsanus tau). In this study, we introduce a reversible method, otolith tipping, to evaluate the presence of binaural inputs. The normal directional response pattern (DRP) was recorded extracellularly for auditory cells in the first‐order descending octaval nucleus (DON) or the midbrain torus semicircularis (TS) using directional stimuli in the horizontal and midsagittal planes. The DRP was re‐evaluated while gently tipping the ipsilateral or contralateral otolith of the saccule to alter the normal relationship with the auditory epithelium. The DRP was also evaluated post‐tipping to ensure no damage had occurred. In the DON, ipsilateral or contralateral tipping most often altered or eliminated spike activity; in the TS, tipping most often caused a change in the shape or orientation of the DRP. The data indicate complex interactions of excitatory and inhibitory inputs, which appear to be associated with the convergence of binaural inputs in the DON and TS. [Work supported by the NIH.]

Sharpening of directional responses along the auditory pathway of the oyster toadfish, Opsanus tau

Our previous studies have shown that the peripheral auditory system of the toadfish encodes the direction of a sound source. Here, we compare directional responses of peripheral saccular afferents, cells in the descending octaval nucleus (DON) of the medulla, and the torus semicircularis (TS) of the midbrain. Recording locations in the brain were labeled with neurobiotin to confirm the site. To compare directional responses among cells, we calculated an index [sharpening ratio (SR)] that weights the relative strength of responses to the best direction for that cell and to the adjacent stimulus angles tested. Unsharpened saccular afferents tend to have a cosinusoidal directional response pattern (DRP) with an expected SR of 0.87. In DON, more than 60% of the cells exhibited directional sharpening (defined as SR <0.8). In TS, more than 80% of the cells exhibited directional sharpening. We conclude that directional auditory sharpening first occurs in DON and some additional sharpening occurs in the ascending pathway to the midbrain, particularly in azimuth. The sharpening of directional selectivity is likely to be an important component of the neural computations underlying directional hearing.

Directional encoding by fish auditory systems.

This paper reviews and discusses several investigations of the peripheral neural code for the directional axis of acoustical particle motion in the saccule of two fishes: goldfish (Carassius auratus) and toadfish (Opsanus tau). Most saccular afferents are directional in the manner of hair cells, having a cosine-shaped directional response pattern. The saccular sensory epithelia are orientated almost vertically in a parasagittal plane. In the horizontal plane, these epithelia are orientated obliquely with respect to the midline. Hair-cell stereocilia project perpendicularly. Thus, directional response patterns of saccular afferents tend to be orientated in azimuth parallel to the orientation of the epithelia in the head. The oblique angle of the toadfish saccule is greater than that of the goldfish, and the range of best directions in the horizontal plane for each species reflects those differing orientations. The azimuth of acoustical particle motion could be computed by comparing the relative activation of the two saccules, as is the case for the ears of most terrestrial vertebrates. The spatial patterns of saccular hair-cell orientation of most fishes thus appear to have little function in azimuthal source location, but for toadfish are probably most important for determining the elevation of monopole sources.

Electrical compensation of the microphone sensitivities in a dual microphone directional hearing aid

Hearing aids with directional sensitivity have shown enhanced user satisfaction for their improved performance in noisy environments. One way to achieve the directional response patterns is to use two omnidirectional microphones with the necessary beamforming electronics to form a beam with the desired directionality. Proper operation of the beamforming circuitry requires that the frequency-dependent sensitivities of the two microphones be accurately matched, or corrected, in both magnitude and phase. This paper presents a method of electrically compensating the response of the two microphones to provide an accurate match for beamforming without the need for special sorting of the pairs for matched response. The circuit is suitable for field recalibration if aging causes the sensitivities to vary, and can also be implemented as an adaptive circuit to update the compensation parameters with time for any slow drift with time.

Single unit recordings from directionally sensitive cells of the torus semicircularis of the goldfish (Carassius auratus)

This experiment characterized the directional responses of cells of the auditory midbrain of goldfish. Single units in the midbrain were characterized by their response to whole-body vibratory stimuli of various directions and amplitudes. The animal’s head was fixed in a rigid dish that was accelerated using two orthogonal pairs of shakers in the horizontal plane, and one shaker oriented vertically. Three orthogonally oriented accelerometers resolved the dish’s motion in azimuth and elevation. Computer-synthesized sinusoids activated the shaker channels with relative phases and amplitudes required to produce linear motion along 12 axes equally spaced over 180° in each of the horizontal, midsagittal, and frontal planes. Spike rate was plotted as a function of stimulation axis angle in both Cartesian and polar coordinates. Most cells showed strongly directional response patterns with a primarily vertical orientation. Response patterns were classified with respect to the symmetry, sharpness, and the amplitude dependence of these directional features. Models were developed to give possible explanations for the observed responses. Many of the response shapes can be explained by combinations of simple peripheral effects (threshold and saturation) and inhibitory interaction. [Work supported by a Program Project Grant (NIH, NIDCD) to the Parmly Hearing Institute.]

Automatic calibrating apparatus and method for second-order gradient microphone

An automatic calibration system for a second-order gradient microphone is provided to ensure optimum sensitivity balance between a pair of first-order gradient microphones mounted in a housing and forming the second-order gradient microphone. Automatic calibration is achieved through use of a transducer also mounted in the housing and located equidistant acoustically between the two first-order gradient microphones. Under the control of a computer, the transducer is directed to generated sound pressure which is used to calibrate the gain of amplifiers respectively associated with each one of the first-order gradient microphones for obtaining maximum directional sensitivity for a second-order directional response pattern. Such a system not only allows the use of inexpensive, non-matched microphones, but also obviates the need for factory calibration. Since the system is configurable to optimize itself automatically prior to use, calibration may be maintained regardless of aging, environmental stresses and parts replacement.

Coherent source location using a pattern diversity technique

A high-resolution pattern diversity method is presented for resolving multiple coherent plane waves impinging on a linear array. In this method, use is made of several different choices for the common directional response or array pattern to form an averaged covariance matrix. A full rank (equal to the number of plane wave arrivals) signal-only covariance matrix can be achieved in the presence of multiple coherent sources, irrespective of the coherence structure. The underlying method does not require a uniform array, and can also be implemented using subarrays to effect the pattern diversity. The theoretical development of the method along with simulation results are provided.

Noise reduction processing arrangement for microphone arrays

A sound processing arrangement couples sound from a prescribed environment through a fixed microphone array to a signal processing arrangement having a specifiable preferred sound source location. The microphone pickup signals are combined with a set of weighting signals to adjust the directional response pattern in successive analysis time intervals. The weighting signals are modified in each analysis time interval so that the total acoustic signal power of the signal processing arrangement output signal is decreased toward a minimum while substantially unity power transfer of sound signals from said preferred location is maintained at all frequencies over a prescribed frequency range. In this way, the preferred source location is in the main beam while unwanted sound source locations are at the null points of the adjusted directional response pattern.

Acoustic diffraction by a variable thickness fluid layer

The effect of a variable thickness, cylindrical, fluid layer on the directional response patterns of a particular acoustic source distribution is investigated. The source consists of an array of parallel line sources on a rigid cylindrical baffle surrounded by a constant thickness cylindrical fluid layer. Located off center of these two cylinders is a third cylinder of a second fluid, which has a variable thickness because it is nonconcentric with the other two. The outer cylinder is surrounded by an infinite medium of the same fluid as the inner cylindrical layer. An analytical solution for the acoustic field is obtained by writing appropriate expressions for the pressure in each region, and applying the boundary conditions between the regions to solve for the unknown modal coefficients in these expressions. The translational addition theorem for cylindrical wavefunctions is used to simplify the matching of boundary conditions on the nonconcentric cylinders. The expression for the farfield pressure is used to produce numerical results for variations of some of the many parameters of the problem.

The theoretical responses of vertical and horizontal line arrays to wind-induced noise in shallow water

A wave theory model for the propagation of noise from a surface source layer has been used to investigate the directional response of vertical and horizontal arrays to wind noise in shallow water. The model assumes an infinite layer of sources radiating sound with pressure directionality of the form cosm α, where m &amp;gt;1 and α is an angle measured from the downward vertical. The field incident on the array is inhomogeneous in the vertical plane, and directional responses have been calculated from the appropriate spatial correlation matrix for various bottom types, sound-speed profiles, and values of m up to 3. Results show that both components of the noise field, the discrete normal modes and the continuous spectrum, can contribute significantly to the total noise level and to the array responses. The mode arrivals give rise to high vertical array responses near broadside and high horizontal array responses towards endfire. Thus considerably different forms of directional response pattern can be produced compared to those predicted by a simple model for ideal conditions. The extent of these differences is strongly dependent on bottom type and on the source directionality parameter m, and slightly dependent on sound-speed profile.

End-fire microphone and loudspeaker structures

Highly directional response patterns can be obtained by connecting microphones or loudspeakers with tubular coupling path structures. The coupling paths comprise a plurality of elements (110,111 . . . 157) arranged in pairs (110,111; 112,113; . . . 156,157) so that for every element (110) below a center line (102) there is an element (111) above the line. Furthermore, the relationship between the element pairs is nonlinear. The desired directional response comprises one main lobe and a plurality of substantially smaller lobes below a determinable threshold value. The elements may be a bundle of tubes (90) or a plurality of apertures (110,111, . . . 157) in a single tube (100).

Directional response pattern simulator

Experiments designed to measure the directional response patterns of acoustic radiators and receivers have basically to be carried out in an anechoic room. If, however, a simulator capable of electrically imitating the real process of forming the directional response pattern is available, one can carry out a directional response determination whenever one wants to. The simulator described here uses a bucket brigade device (BBD) and other electronic components. A technique for describing the polar diagram of the directional response pattern is also discussed. Model experiments for obtaining the simple directional response patterns and for suppressing the side lobe can be successfully carried out with the aid of such a simulator.

Directivity of a long line array with periodically missing sensors

A proposed design of a very long line array of 80 sensors, spaced one‐half wavelength apart, envisioned the array as being comprised of four equal subarrays that would be connected together mechanically and electrically. However, mechanical considerations dictated that every twentieth sensor would be eliminated and replaced by mounting hardware. Computations of the directional response pattern of this perturbed array indicated the annoying presence of numerous grating‐type lobes that could not be eliminated or even substantially reduced by changing the amplitude weightings. By a simple superposition consideration, i.e., that the array in question is the sum of an intact 80 sensor array and a second array of four negative amplitude sensors, each spaced ten wavelengths apart, the number, bearing, and amplitude of these grating‐type lobes can be easily predicted. [Work sponsored by NAVSEA 63 R1.]

Radiation from a spherical acoustic source near a scattering sphere

The radiation from a spherical source vibrating with an arbitrary, axisymmetric, time-harmonic velocity distribution while positioned at an arbitrary point wholly outside a fluid sphere while both are embedded in another infinite fluid medium, is computed. The translational addition theorem for spherical wave functions is used to express series of wave modes centered at one sphere in terms of modes centered at the other, thereby facilitating the task of satisfying the boundary conditions. By letting the fluid sphere become either infinitely dense or infinitely compliant, the special cases of a spherical source radiating in the presence of a perfectly reflecting spherical scatterer are obtained. The source output and farfield directional response pattern are computed as a function of source and fluid sphere separation for some representative values of relative fluid density and sound speed. Numerous results are presented showing the modification of the radiation load on monopole and dipole sources of various wavelength sizes due to a nearby rigid or pressure release, spherical scatterer of the same size. The effect of the perfect scatterer is only important when the source and scatterer are very close and the pressure-release scatterer has considerably more effect than the rigid one. Subject Classification: [43]20.30, [43]20.55.

Tilted directional response patterns formed by amplitude weighting and a single 90° phase shift

It is shown that by appropriately processing the output signals of the elements in a symmetric array, a tilted sum pattern or difference pattern can be produced without numerous delay lines or phase-shift networks. The tilted pattern is achieved by combining, in proper phase, two outputs of an array; the first output is that of a particular amplitude weighted phase-symmetric array while the second is that of a particular amplitude weighted phase-antisymmetric array. To achieve the proper phase relationship between these two outputs, one of them must be phase shifted by ±90°. Theoretical calculations and experimental results are presented for the case of a line array of nine elements that are equally spaced a half-wavelength apart; both a sum pattern and a difference pattern tilted to 30° from the normal to the line array, by this method, are shown. The variation of the side-lobe levels of these tilted patterns is examined as the ±90° phase shift is perturbed. The possibility of using this technique to continuously vary the angle of tilt is discussed. Subject Classification: [43]20.55; [43]30.50; [43]60.30; [43]35.54.

On the use of delays for wide-band superdirective beam forming in endfire and broadside arrays

In algebra, the values of a polynomial over a wide span of time can be inferred from its value and that of its derivatives, measured over a very short span of time. Somewhat analogously, closely-spaced measurements, defining the fine structure of the phase and amplitude distribution over a narrow antenna aperture, can provide the information conventionally obtained from a similar number of elements spaced at half-wavelength intervals over a wider aperture.Superdirective beam patterns, exploiting this principle, are conveniently synthesized by defining the directions in which zero (or minimum) response is required. The correlation between closely-spaced measurements will then cause some reduction of gain, even at the wanted peak of the directional response pattern, but the directivity, i.e. the gain in the wanted direction relative to that in other directions, can be significantly enhanced.Each direction of arrival produces a corresponding pattern of relative propagation delays to the different elements of an array. By suitably equalizing these with non-dispersive delay circuits and then subtracting for null-forming (in place of the usual phase changers), such superdirective arrays can be designed for bandwidths of up to several octaves. Thus superdirectivity can be of considerable value, in certain circumstances, for h.f. radio, sonar or radar.