Acoustic Centers Research Articles

Neural connections of the torus semicircularis in the adult Zebrafish.

The torus semicircularis (TS) of teleosts is a key midbrain center of the lateral line and acoustic sensory systems. To characterize the TS in adult zebrafish, we studied their connections using the carbocyanine tracers applied to the TS and to other related nuclei and tracts. Two main TS nuclei, central and ventrolateral, were differentiable by their afferent connections. From central TS, (TSc) numerous toropetal cells were labeled bilaterally in several primary octaval nuclei (anterior, magnocellular, descending, and posterior octaval nuclei), in the secondary octaval nucleus, in the caudal octavolateralis nucleus, and in the perilemniscular region. In the midbrain, numerous toropetal cells were labeled in the contralateral TSc. In the diencephalon, toropetal cells labeled from the TSc were observed ipsilaterally in the medial prethalamic nucleus and the periventricular posterior tubercle nucleus. TSc toropetal neurons were also labeled bilaterally in the hypothalamic anterior tuberal nucleus (ATN) and ipsilaterally in the parvicellular preoptic nucleus but not in the telencephalon. Tracer application to the medial octavolateralis nucleus revealed contralateral projections to the ventrolateral TS (TSvl), whereas tracer application to the secondary octaval nucleus labeled fibers bilaterally in TSc and neurons in rostral TSc. The TSc sends ascending fibers to the ipsilateral lateral preglomerular region that, in turn, projects to the pallium. Application of DiI to the optic tectum labeled cells and fibers in the TSvl, whereas application of DiI to the ATN labeled cells and fibers in the TSc. These results reveal that the TSvl and TSc are mainly related with the mechanosensory lateral line and acoustic centers, respectively, and that they show different higher order connections.

Measuring directivity of half-inch measurement microphones

The directivity of a microphone is the relative sensitivity variation as a function of incidence angle. This is an important characteristic when every sound arriving at the microphone position is relevant. This paper presents the measuring directivity of half-inch measurement microphones. The microphone is placed in a free sound field and exposed to a sound pressure. The unloaded output voltage is measured. Then, the microphone is rotated in 30o steps, while both the acoustic centers of the microphone and the sound source remain in fixed positions in the sound field, and is exposed to the same sound pressure. The unloaded output voltage for each angle of incidence is measured and them the difference relative to 0 deg. of incidence is calculated as a function of frequency. The directivity of eight measurement microphones from the same manufacturer but of different types and frequency response characteristics (i.e. pressure field, random incidence or free-field) were measured. Results showed that the microphones object of this investigation have similar directivities in the frequency range from 16 Hz to 12.5 kHz regardless of their frequency response characteristics.

Diffraction of directional sources by rigid wedges or barriers.

The secondary-edge-source method (SESM) has found widespread application in predicting edge diffraction. The method, however, is limited to point sources. Based on the concept of weighted summation of diffractive contribution from each propagation path, this letter extends the SESM to directional sources with equivalent acoustic centers. The validity of the proposed method is demonstrated by comparing theoretical results to those obtained using the omnidirectional monopole superposition method.

Acoustic source centering of musical instrument directivities using acoustical holography

The acoustic center of a source is commonly defined as the point from which spherical wavefronts appear to diverge. Measuring directivities of sound sources with a surrounding spherical array whose geometric origin is not aligned with the acoustic center of the source can lead to distortions in directivity patterns. Thus, a method is desired to obtain both the far-field directivity pattern and to determine the acoustic center of a source. This work illustrates how acoustical holography can identify the reference frame from which spherical waves diverge by studying various musical instruments' acoustic centers.

Precision enhancement in source localization using a double-module, three-dimensional acoustic intensity probe

The three-dimensional (3D) acoustic intensity probe is not popularly used for the source localization of acoustic source because of the large error even though the technique has been well known. In particular, the measured direction-of-arrival strongly depends on the frequency, which is a detrimental drawback that hampers the use of this method. Such spectral bias error, due to the discrete positioning and spacing of sensors surrounding the acoustic center, fluctuates in a nearly regular spectral pattern when a 3D acoustic intensity probe configured in a tetrahedral shape is used. In this work, two error compensation methods are tried: The first method is to adopt a double-module configuration, which is formed by the connected assembly of two intensity modules, but with different locations of acoustic centers for a spatial averaging effect. The second one is the 1/3-octave band averaging of the measured intensity spectrum within the effective measurement range. Because two probe modules are attached, they concatenate 1–3 sensors in the overlap position. Four double-module probes different in assembly configuration of involved two single-modules are tested: modules having a same acoustic center but twisted by 60°, inverted modules sharing one microphone and twisted by 60°, symmetric modules having the joint angle of 60° in the sharing edge, symmetric modules to a common face thus sharing three microphones. Measurements are conducted in an anechoic chamber by changing the source positions for 4 azimuth and 3 elevation angles. The results reveal that the maximum mean bias error of about 4° can be obtained by the double-module 3D acoustic intensity method, depending on the module configuration and angular source position. This contrasts to the fluctuating direction-of-arrival within about ±10° error range, which is obtained by each single-module in a concatenated double-module. In particular, when the band averaging technique is applied to the measured data by the probe module composed of the inverted single modules, the maximum bias error can be reduced to less than 1° in both azimuth and elevation angles.

Estimation of the source distance using the multiple three-dimensional acoustic intensimetry

A 3D acoustic intensimetry (AI) in tetrahedral configuration can be used for the source localization. Such a 3D AI module is compact, but it can also yield a precise bearing angle for the low Helmholtz numbers if some bias errors are compensated. In this study, besides the bearing angle, the source distance is estimated by using the multiple 3D AI probes with different acoustic centers. Because each AI module indicates a vector from the acoustic center to the source direction, the nearest point between any pair of line vectors can approximate the source position. The source position can be estimated by minimizing the least square error of the positions determined by multiple intensity vectors. Such idea is preliminarily tested with four 3D AI modules, of which each module is composed of 4 MEMS microphones separated by 30 mm. Four 3D AI modules are also arranged in a tetrahedron layout, and the source frequency range is 0.5–2 kHz. The distance between modules is varied for 150–250 mm range, and the source distance for 1–4 m range. Current test results reveal that the estimation error is less than about 2, 5, and 7% when the elevation angle is within 0–30°, 30–60°, 60–90°, respectively.

Collinearity and Sample Coverage Issues in the Objective Measurement of Vocal Quality: The Case of Roughness and Breathiness.

The aim of the study was to address the reported inconsistencies in the relationship between objective acoustic measures and perceptual ratings of vocal quality. This tutorial moves away from the more widely examined problems related to obtaining the perceptual ratings and the acoustic measures and centers in less scrutinized issues regarding the procedure to establish the correspondence. Expressions for the most common measure of association between perceptual and acoustic measures (Pearson's r) are derived using a multiple linear regression model. The particular case where the multiple linear regression involves only roughness and breathiness is discussed to illustrate the issues. Most problems reported regarding inconsistent findings in the relationship between given acoustic measures and particular perceptual ratings could be linked to sample properties not directly related to the actual relationship. The influential sample properties are the collinearity between the regressors in the multiple linear regression and their relative variances. Recommendations on how to rule out this possible cause of inconsistency are given, varying in scope from data collection, reporting, manipulation, and results interpretation. The problems described can be extended to more general cases than the exemplified roughness and breathiness sample's coverage. Ruling out this possible cause of inconsistency would increase the validity of the results reported.

From Umwelt to Soundtope: An Epistemological Essay on Cognitive Ecology

Capturing information means for every organism acquiring knowledge about the living and not living objects that exist in its surroundings. In this way, the “historical” concept of Umwelt, as a subjective surrounding has been recently integrated in the theory of landscape ecology where a landscape is not only a geographical entity but also a cognitive medium. The landscape may be considered a semiotic context used by the organisms to locate resources heterogeneously distributed in space and time. In particular, inside a landscape there are different eco-fields defined as spatial arrangements of objects carrier of meaning that organisms utilize to track resources. Along this epistemic path the sonic component of the landscape is an important carrier of information commonly used by the majority of animal species to managing many vital functions. In particular birds, which are animals with a complex system of acoustic communication, seem to organize acoustic centers for public information. These sonic patterns (soundtopes) are characterized by a great variability in space and time and function like a special eco-field that allows species to share information about the status of resources and the dynamics of populations. The availability of such public information avoids a deeper and more expensive exploration of the environment to assess its quality.

Measurement of the sensitivity phase-frequency characteristics of hydrophones by the reciprocity method

Some new approaches for phase calibration of hydrophones by the reciprocity method are considered. Uses of this method for measuring the phase angle of the sensitivity for the geometric and acoustic centers of a hydrophone and for determining the position of the acoustic center from its shift relative to the geometric center of a hydrophone are described. Results from an experimental test of these techniques are presented.

50 kHz 체장어군탐지기용 분할 빔 음향 변환기의 개발

An improved split-beam transducer for a 50 kHz fish-sizing echo sounder was developed. The main objective of this study was to minimize the side lobe level in the beam pattern and the distance between acoustic centers for adjacent transducer quadrants in the geometrical arrangement of array elements while maintaining a given number of transducer elements and beam width. To achieve these goals, a 32-element planar array transducer (<TEX>$6{\times}6$</TEX> array with one element in each corner missing) was designed using the Dolph-Chebyshev shading function to suppress side lobes in the array beam pattern and fabricated by arranging the inter-element spacing to be substantially equal to half the wavelength using the transducer element of 0.4 times the wavelength in diameter. The performance characteristics of this split-beam transducer were evaluated in the experimental water tank of <TEX>$5m{\times}5m{\times}6m$</TEX> (length<TEX>${\times}$</TEX>height<TEX>${\times}$</TEX>width). In this study, the design goal of the beam width and side lobe level for transmitting a beam pattern was initially set at <TEX>$21^{\circ}$</TEX> and -30 dB, respectively. However, the measured beam width at 3 dB was <TEX>$21^{\circ}$</TEX> in both directions with side lobe levels of -24.7 dB in the horizontal plane and -25.6 dB in the vertical plane. The averaged beam width at -3 dB of the receiving beam patterns for four receiving quadrants was <TEX>$31.4^{\circ}$</TEX>. The transmitting voltage response was 161.5 dB (re <TEX>$1{\mu}Pa$</TEX>/V at 1 m) at 50.23 kHz with a bandwidth of 2.16 kHz, and the averaged receiving sensitivity for four receiving quadrants was -178.13 dB (re 1 V/<TEX>${\mu}Pa$</TEX>) at 49.8 kHz with a bandwidth of 2.64 kHz.

50 kHz 체장어군탐지기용 분할 빔 음향 변환기의 지향성 보정 및 위치각 추정

The most satisfactory split-beam transducer for fish sizing maintains a wide bearing angle region for correct fish tracking without interference from side lobes and lower sensitivity to fish echoes outside of the main lobe region to correctly measure the angular location of free-swimming fishes in the sound beam. To evaluate the performance of an experimentally developed 50 kHz split-beam transducer, the angular location of a target was derived from the electrical phase difference between the resultant signals for the pair of transducer quadrants in the horizontal and vertical planes consisting of 32 transducer elements. The electrical phase difference was calculated by cross-spectral density analysis for the signals from the pair of receiving transducer quadrants, and the directivity correction factor for a developed split-beam transducer was estimated as the fourth-order polynomial of the off-axis beam angle for the angular location of the target. The experimental results demonstrate that the distance between the acoustic centers for the pair of receiving transducer quadrants can be controlled to less than one wavelength by optimization with amplitude-weighting transformers, and a smaller center spacing provides a range of greater angular location for tracking of a fish target. In particular, a side lobe level of -25.2 dB and an intercenter spacing of <TEX>$0.96\lambda$</TEX>(<TEX>$\lambda$</TEX>= wavelength) obtained in this study suggest that the angular location of fish targets distributing within a range of approximately <TEX>${\pm}28^{\circ}$</TEX> without interference from side lobes can be measured.

Estimation of pressure-particle velocity impedance measurement uncertainty using the Monte Carlo method

The pressure-particle velocity (PU) impedance measurement technique is an experimental method used to measure the surface impedance and the absorption coefficient of acoustic samples in situ or under free-field conditions. In this paper, the measurement uncertainty of the the absorption coefficient determined using the PU technique is explored applying the Monte Carlo method. It is shown that because of the uncertainty, it is particularly difficult to measure samples with low absorption and that difficulties associated with the localization of the acoustic centers of the sound source and the PU sensor affect the quality of the measurement roughly to the same extent as the errors in the transfer function between pressure and particle velocity do.

Electro-acoustic converter with demountable diaphragm and voice coil assembly

A compound loudspeaker drive unit comprising a first drive unit and a second drive unit arranged co-axial with respect to the center axis of the loudspeaker, and each drive unit comprises permanent magnet means and pole piece means together forming a magnetic circuit with a pole gap for exciting a voice coil assembly, each pole gap providing magnetic field directed radially with respect to a center axis of the loudspeaker. At least one of the permanent magnet means has a radially extending magnetization direction with respect to said center axis of the loudspeaker and the acoustic centers of said drive units substantially coincide.

Calibration of apparatus for wave separation in wind instruments

Knowledge of the forward and backward traveling waves inside the bore of a wind instrument is a useful starting point for the estimation of its playing parameters. These are mainly parameters describing the mouthpiece embouchure and the states of the tone holes. Due to the highly nonlinear behaviour of the excitation mechanism, a precise estimation is needed. The separation method under investigation relies on a model inversion, starting from the pressure measured by three microphones. For this reason the estimation is very sensitive to the relative positions of the microphones, and the latter must therefore be known very precisely. A geometrical measurement would not be reliable because of construction tolerances, including uncertainties about the acoustic centers of the microphones; therefore the distances are gathered through audio measurements. A number of approaches to such a calibration of the measurement system have been investigated, using a purposely constructed apparatus which will also be described.

Imaging acoustic centers of the dolphin brain with positron emission tomography

In human subjects, positron emission tomography (PET) has been used in diagnosis of disease, in studies of complex cognitive tasks, and in localizing areas of sensory activation, motor movement, and attention. Now, brain physiology of bottlenose dolphins, Tursiops truncatus, has been studied with PET. The dolphin brain is in the human size range but is more highly convoluted. The known acoustic centers of the dolphin brain are greatly enlarged compared with human brains. However, dolphins have a multi-tiered cortex with an extensive extra lobe, the paralimbic lobe, which does not occur in mammals or other animals outside the Order Cetacea. Because of its inaccessible location, there are no functional studies of the paralimbic cortex. PET offers an opportunity to study activity in this unique part of the dolphin brain during various stimulus conditions that may help to reveal functional aspects of the paralimbic cortex. For experimental scans, the dolphin was exposed to acoustic stimuli (tones or pulses) to reveal areas of relative brain metabolism after 18-F-FDG administration. These scans have revealed interesting features of the living dolphin brain including the paralimbic lobe as well as known acoustic areas in the cortex, midbrain, and acoustic nuclei.

On the interference between the two microphones in free-field reciprocity calibration

One of the fundamental assumptions in free-field reciprocity calibration of microphones is that the microphones can be substituted by point sources at the positions where the acoustic centers are located. However, in practice the microphones have finite dimensions and, at the distance and in the frequency range where the measurements are made, the direct wave and the subsequent reflections from the microphones interfere with each other, creating a “standing wave.” This interference effect gives rise to deviations from the inverse distance law, indicating that the free-field assumption is not strictly valid. The interference has been thought to be caused by specular reflection between the parallel diaphragms of the microphones, and a solution based on tilting the axis of one of the microphones a few degrees has been proposed, but never examined in practice. In this paper a time-selective technique is applied for analyzing the interference and for removing it in the time domain. It is shown that the phenomenon is due to multiple backscattering rather than specular reflection. Thus tilting one of the microphones does not alleviate the problem, as also demonstrated experimentally. However, the time-selective technique is quite effective in removing the interference effect and other disturbances from the direct wave between the microphones.

A time-selective technique for free-field reciprocity calibration of condenser microphones.

In normal practice, microphones are calibrated in a closed coupler where the sound pressure is uniformly distributed over the diaphragm. Alternatively, microphones can be placed in a free field, although in that case the distribution of sound pressure over the diaphragm will change as a result of the diffraction of the body of the microphone, and thus, its sensitivity will change. In the two cases, a technique based on the reciprocity theorem can be applied for obtaining the absolute sensitivity either under uniform pressure or free-field conditions. In this paper, signal-processing techniques are considered that improve the accuracy of the free-field calibration method. In particular, a fast Fourier transform (FFT)-based time-selective technique for removing undesired reflections from the walls of the measurement chamber has been developed and applied to the electric transfer impedance function between two microphones. The acoustic centers of the microphones have been determined from the "cleaned" transfer impedance values. Then, the complex free-field sensitivities of the microphones have been calculated. The resulting complex sensitivities and acoustic centers have proved to be in good agreement with previously published data, and this confirms the reliability of the time-selective technique, even in nonanechoic environments. Furthermore, the obtained results give a new reference for further comparisons, because they cover a frequency range with an accuracy that has not been obtained by previously published data.

Increased glutamate, GABA and glutamine in lateral geniculate nucleus but not in medial geniculate nucleus caused by visual attention to novelty

This study is concerned with cortico-thalamic neural mechanisms underlying attentional phenomena. Previous results from this laboratory demonstrated that the visual sector of the GABAergic thalamic reticular nucleus is selectively c- fos activated in rats that are naturally paying attention to features of a novel-complex environment, and that this activation is dependent on top-down glutamatergic inputs from the primary visual cortex. By contrast, the acoustic sector of the thalamic reticular nucleus is not activated despite noise generated by exploration and c- fos activation of brainstem acoustic centers (e.g. dorsal cochlear nucleus, inferior colliculus). A prediction of these results is that the levels of the neurotransmitters glutamate and GABA, and the glutamate-related amino acid glutamine, will be increased in the lateral geniculate nucleus (LGN), but not in the medial geniculate nucleus (MGN) of rats that explore a novel-complex environment in comparison to levels of these amino acids in control rats. By means of neurochemical analysis of these amino acids (HPLC) the results of this study confirmed this prediction. The results are consistent with the previously proposed ‘focal attention’ hypothesis postulating that a focus of attention in the primary visual cortex generates top-down center-surround facilitatory-inhibitory effects on geniculocortical transmission via corticoreticulogeniculate pathways. The results also supports the notion that a main function of corticothalamic pathways to relay thalamic nuclei is attention-dependent modulation of thalamocortical transmission.

Relationship between the diffraction constants, the reciprocity parameter, and the mutual radiation impedance of a pair of compact radiators: An improved Pritchard approximation

By the principle of reciprocity, the mutual radiation impedance matrix of an acoustical array in a stationary fluid must be symmetric. However, use of the classical ‘‘Pritchard approximation’’ to compute array mutual (mechanical) radiation impedance (Zmut=j Re[Zself]e−jkd/kd; ejωt assumed) [R. L. Pritchard, J. Acoust. Soc. Am. 32, 730–737 (1960)] leads to a matrix which is not symmetric for nonidentical radiators. Also, it is restricted to low frequencies (ka≪1). By a simple application of the principle of reciprocity, it is shown that the mutual mechanical radiation impedance of a pair of reasonably compact radiators in an otherwise unbounded stationary fluid is expressible in terms of their (complex) diffraction constants D1 and D2 and the (complex) spherical wave reciprocity parameter Js as Zmut=S1S2D1D2/Js, where S is the radiator surface area, Jsf=2d/jρf, d is the separation between radiator acoustic centers, ρ is the fluid density, and f is the frequency. (For mutual acoustical radiation impedance, simply drop the factors S1 and S2.) For spherical radiators of radius a, D(1+n=ejkan/jkan). Note, this newly derived form for Zmut is guaranteed to be reciprocal. Also, for small ka, it reduces to S1S2/Js, which is equivalent to the classical Pritchard approximation, corrected for nonidentical radiators.

Comparison of simulation and measured sound system performance in the German Reichstag Debate Hall, Berlin

For the design of the new sound system for the Reichstag Debate Hall, Berlin, the ulysses computer aided acoustic design program has been used. The 3-D model of the room consisted of more than 1000 faces treated with different absorption in octave bands according to the architect’s plans. Simulation of direct sound coverage, RT60, intelligibility, energy decay via ray-tracing, etc., was done to evaluate different solutions of the sound system designs and their interaction with room acoustics. It is intended to compare actual acoustic test results to simulated predictions and to discuss conformity and deviations. The software was also used to predict directivity balloons of the complex speaker arrays located in the debate hall. The balloons were derived from measured balloons of the single devices used in the arrays. Considering relative mechanical locations, acoustic centers, acoustic power, and delays, the predictions showed good conformity with polar measurements of a real cluster.