摘要:

The structural intensity technique can directly measure and distinguish power transmissions between different structural wavetypes across a joint, and its applications are numerous in practical engineering. In this paper, a new method is proposed for the measurement of coupling loss factors (CLFs) using the structural intensity technique. An outline of the method’s theory is also given. Theoretically the proposed method gives an approximate estimation of CLFs. The approximate error depends on the ratios of the effective modal overlap factor of the receiving subsystem to the modal overlap factors of the subsystems coupled through the joint of interest. If the effective modal overlap factor of the receiving subsystem is large compared with the modal overlap factors of the coupled subsystems, the approximate error is small and negligible. A series of measurements were carried out to verify the outlined theory. The results measured on the joints with two subsystems showed that this proposed method can be used to accurately measure CLFs when the modal overlap factor of the receiving subsystem is larger than that of the source subsystem. The approximate error decreases with increasing frequency and the modal overlap factor ratio of the receiving subsystem to the source subsystem.

ISSN:0001-4966    

DOI:10.1121/1.421096

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A mathematical model is developed for the prediction of the forced response of finite plates to in-plane point force excitations. The model illustrates the nature of the coupling between in-plane longitudinal and in-plane shear waves and the resonant characteristics of the in-plane vibrational behavior of finite flat plates. The predicted resonance frequencies and mode shapes are compared against the finite element results and good agreement is found. The mode shapes of the in-plane vibration are depicted for frequencies below and above the first resonance frequency. It is illustrated by example that the input power due to in-plane force excitation at the in-plane resonance frequencies is at the same level as that due to out-of-plane force excitations at the flexural resonances in the same frequency band. The participation of the longitudinal and in-plane shear waves in transmitting the vibrational power and the resulting circulatory pattern of structural intensity is also presented.

ISSN:0001-4966    

DOI:10.1121/1.421120

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Diagrammatic multiple-scattering theory is applied to the calculation of ensemble average square responses in an infinite homogeneous plate in flexure attached to a random distribution of undamped sprung masses. This system is a prototypical example of a wave-bearing master structure with a locally reacting “fuzzy” substructure. Results for mean fields were obtained in an earlier work. Here it is found that fluctuations away from the mean are weak if the spectral and areal number density of sprung masses is great. A radiative transfer equation is found to govern the flow of energy on time scales greater than the inverse of the frequency, and a diffusion equation is found to govern the flow of energy at times greater than the dwell time of energy in the substructure. The diffusion rate is very slow if the dwell time in the substructure is long. The effect of true damping on these results is discussed.

ISSN:0001-4966    

DOI:10.1121/1.421097

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

This paper is concerned with the analysis and design of a feedback control active eardefender. By using classical control theory, the authors investigated the system stability and robustness of stability, the noise reduction level and its parameter sensitivity, and the working frequency range of the active eardefender. A general method for designing a stable feedback control eardefender is developed. In this theory, a special type of second-order compensator is used to improve the robustness of stability, the noise reduction level and its robustness, and the working area of the active eardefender, particularly at the low-frequency range of interest.

ISSN:0001-4966    

DOI:10.1121/1.421125

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

This paper reports on the influence of individual reflections on the auditory spatial aspects of reproduced sound. The sound field produced by a single loudspeaker positioned in a normal listening room has been simulated using an electroacoustical synthesis of the direct sound, 17 individual reflections and the reverberant field. The threshold of detection was measured using the method of adjustment for five reflections using three subjects for noise and speech. The thresholds have been measured for two simulated situations (1) a loudspeaker with a frequency independent directivity characteristics and frequency independent absorption coefficients of the room surfaces and (2) a loudspeaker with directivity similar to a standard two-way system and absorption coefficients according to measurements of real materials. The results have shown that subjects can reliably distinguish between timbre and spatial aspect of the sound field, that the spectral energy above 2 kHz of the individual reflection determines the importance of the reflection for the spatial aspects, and that only the first order floor reflection will contribute to the spatial aspects.

ISSN:0001-4966    

DOI:10.1121/1.421098

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The three-transducer free-field reciprocity calibration technique has been extended to apply to ultrasonic transducers operating in air at frequencies above 100 kHz. The reciprocity method was extended to apply to this frequency range by correcting for attenuation, which is severe in air, and for diffraction. Validation of the extended reciprocity calibration technique was performed by comparing experimental determinations of receive and transmit sensitivity with predictions obtained from a mathematical model for the test transducers and calibration system. It is believed that these are the first comprehensive, broadband experimental determinations of absolute transmit and receive sensitivity to appear in the technical literature for transducers operating in air over the frequency range 100–500 kHz. Receive and transmit sensitivity measurements obtained with the extended reciprocity calibration technique agreed to within 2.5 dB of model predictions. The location of the resonance peaks in the sensitivity measurements had a maximum difference of 7% from those inferred from measurements of transducer admittance and those predicted by the transducer model. It was concluded that both the extended reciprocity calibration technique and the transducer model were accurate to within this level of discrepancy.

ISSN:0001-4966    

DOI:10.1121/1.421099

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Allen et al. [Abstract inEighteenth Midwinter Research Meeting of the Association for Research in Otolaryngology, Des Moines, IA (1995)] have found that the ear canal reflectance passes through a minimum around the frequency of a spontaneous otoacoustic emission (SOAE). They considered this result to constitute evidence against active nonlinear cochlear function as the basis for SOAEs. In order to investigate theoretically the expected behavior of ear canal reflectance in the neighborhood of a SOAE associated with an active-nonlinear cochlea, we use a simplified model in which the ear drum end of the ear canal is effectively terminated by a nonlinear-active element. Under the influence of a sinusoidal driver at the entrance of the ear canal, this element will, to a good approximation, either (1) oscillate at both the frequency of the driver (at which the reflectance is determined) and the SOAE (at a suppressed level, corresponding to nonentrainment), or (2) be entrained and only oscillate at the driving frequency. The magnitude of the nonlinear ear canal reflectance is found to exceed unity only at sufficiently low stimulus levels, and occurs under conditions of entrainment and nonentrainment of the spontaneous emission. Otherwise, the reflectance is less than unity and, as a function of frequency, has a minimum around the SOAE frequency.

ISSN:0001-4966    

DOI:10.1121/1.421121

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

There is some controversy in the literature over whether the so-called “active mechanism” or “cochlear amplifier” is actually a power amplifier that can produce an output signal with more power than its input, or whether it simply minimizes dissipative losses within the cochlea without providing an actual power gain greater than unity. A corollary of this controversy is whether spontaneous otoacoustic emissions (SOAEs) represent the output of a nonlinear oscillator mechanism, i.e., a power amplifier which can produce an oscillatory output signal in the absence of an input oscillatory signal, or whether they represent the output of a noise-driven, passive, nonlinear system. This paper describes measurements of energy reflectance and acoustic impedance in the ear canals of human subjects with strong SOAEs. The reflectance, and the resistive and reactive parts of the acoustic impedance, all show a frequency fine structure which correlates with SOAE frequencies, and which becomes more pronounced at low stimulus levels. In some ears at some SOAE frequencies, energy reflectance exceeds unity, and correspondingly, acoustic resistance is negative. This result demonstrates that there is a power gain at these frequencies: The power reflected from the cochlea to the ear canal exceeds the power incident. It is also consistent with the theory that these SOAEs are produced by a nonlinear oscillator mechanism in the cochlea.

ISSN:0001-4966    

DOI:10.1121/1.421122

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A model was developed that simulates the binaural response properties of low-frequency inferior colliculus (IC) neurons in response to several types of stimuli. The model incorporates existing models for auditory-nerve fibers, bushy cells in the cochlear nucleus, and cells in medial superior olive (MSO). The IC model neuron receives two inputs, one excitatory from an ipsilateral MSO model cell and one inhibitory from a contralateral MSO model cell. The membrane potential of the IC model neuron (and the other model neurons) is described by Hodgkin–Huxley type equations. Responses of IC neurons are simulated for pure-tone stimuli, binaural beat stimuli, interaural phase-modulated tones, single binaural clicks, and pairs of binaural clicks. The simulation results show most of the observed properties of IC discharge patterns, including the bimodal and unimodal interaural time difference (ITD) functions, sensitivities to direction and rate of change of ITD, ITD-dependent echo suppression, and early and late inhibitions in response to clicks. This study demonstrates that these response properties can be generated by a simple model incorporating ITD-dependent excitation and inhibition from binaural neurons.

ISSN:0001-4966    

DOI:10.1121/1.421100

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The inferior colliculus (IC) model of Cai et al. [J. Acoust. Soc. Am.103, 475–493 (1998)] simulated the binaural response properties of low-frequency IC neurons in response to various acoustic stimuli. This model, however, failed to simulate the sensitivities of IC neurons to dynamically changing temporal features, such as the sharpened dynamic interaural phase difference (IPD) functions. In this paper, the Reference 1998 model is modified such that an adaptation mechanism, viz., an additional channel simulating a calcium-activated, voltage-independent potassium channel which is responsible for afterhyperpolarization, is incorporated in the IC membrane model. Simulations were repeated with this modified model, including the responses to pure tones, binaural beat stimuli, interaural phase-modulated stimuli, binaural clicks, and pairs of binaural clicks. The discharge patterns of the model in response to current injection were also studied and compared with physiological data. It was demonstrated that this model showed all the properties that were simulated by the Reference 1998 model. In addition, it showed some properties that were not simulated by that model, such as the sharpened dynamic IPD functions and adapting discharge patterns in response to current injection.

ISSN:0001-4966    

DOI:10.1121/1.421130

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP