Acoustic Transfer Function Research Articles

Propeller-shaft-hull coupling acoustic radiation characteristics induced by friction self-excitation of the stern bearing

This paper focuses on the practical engineering problem of excessive propeller-shaft-hull coupling vibration noise, which is caused by poor lubrication contact of water-lubricated stern bearings in the ship propulsion shaft system. Firstly, based on the three-dimensional sono-elasticity theory of ships, calculation models for the propeller-shaft-hull coupling acoustic radiation transfer function are established separately, considering the propeller excitation and friction excitation of the stern bearing. Secondly, by analyzing the acoustic radiation contribution of each mode, the vibration mode with the highest contribution to the typical acoustic radiation transfer function peaks of the propeller-shaft-hull coupling under the friction excitation of the stern bearing is separated. The spatial distribution and pointing characteristics of the sound field corresponding to the propeller-shaft-hull coupling acoustic under friction excitation of the stern bearing are given. Finally, a quantitative evaluation model of propeller-shaft-hull coupling acoustic radiation caused by friction self-excitation of the stern bearing is established. The mechanism behind the typical acoustic radiation peaks of propeller-shaft-hull coupling under friction excitation of the stern bearing is revealed, which provides methodological guidance for the quantitative evaluation of friction vibration noise and the separation of vibration noise components in ship stern structures.

Exploring the limits of virtual source localization with amplitude panning on a flat panel with actuator array: Implications for future researcha).

Immersive and spatial sound reproduction has been widely studied using loudspeaker arrays. However, flat-panel loudspeakers that utilize thin flat panels with force actuators are a promising alternative to traditional coaxial loudspeakers for practical applications, with benefits in low-visual profiles and diffuse radiation. Literature has addressed the sound quality and applications of flat-panel loudspeakers in three-dimensional sound reproduction, such as wave field synthesis and sound zones. This paper revisits the spatial sound perception of flat-panel loudspeakers, specifically the localization mismatch between the perceived and desired sound directions when using amplitude panning. Subjective tests in an anechoic chamber with 24 subjects result in the mean azimuth direction mismatch within ±6.0° and the mean elevation mismatch within ±10.0°. The experimental results show that the virtual source created by amplitude panning over a flat-panel loudspeaker still achieves spatial localization accuracy close to that of a real sound source, despite not using complex algorithms or acoustic transfer function information. The findings of this study establish a benchmark for virtual source localization in spatial sound reproduction using flat-panel loudspeakers, which can serve as a starting point for future research and optimization of algorithms.

Minimally invasive ossiculoplasty via an endoscopic transtympanic approach

IntroductionThe aim of this study was to evaluate the feasibility of ossiculoplasty via a minimally invasive endoscopic transtympanic approach (ETTA). Case seriesWe investigated the exposure of target structures (incus and stapes) on 4 human temporal bones by placing an endoscope into the middle ear cleft through the 4 tympanic quadrants. Then, on 3 additional specimens, we performed an incudostapedial disjunction and repaired it with a drop of hydroxyapatite cement via ETTA. We measured the size of tympanic perforation, and the acoustic transfer function of the middle ear (125–8000Hz) before and after repair by placing an insert in the external auditory canal and recording the acoustic signal in the utricle by a microphone. The acoustic signal gain was estimated in dB μV. Exposure was similar in all four quadrants but ergonomics was better with a posteroinferior myringotomy. Ossicular chain repair was conducted successfully in all cases and the acoustic transfer function of the middle ear was significantly improved. Residual tympanic perforation (n=3) was 2±0.3mm in diameter. ConclusionETTA to reconstruct incudostapedial joint with bone cement was feasible and effective. It opens perspectives for robot-based procedures guided by augmented reality.

Comparative Analysis of HRTFs Measurement Using In-Ear Microphones.

The head-related transfer functions (HRTFs) describe the acoustic path transfer functions between sound sources in the free-field and the listener's ear canal. They enable the evaluation of the sound perception of a human being and the creation of immersive virtual acoustic environments that can be reproduced over headphones or loudspeakers. HRTFs are strongly individual and they can be measured by in-ear microphones worn by real subjects. However, standardized HRTFs can also be measured using artificial head simulators which standardize the body dimensions. In this paper, a comparative analysis of HRTF measurement using in-ear microphones is presented. The results obtained with in-ear microphones are compared with the HRTFs measured with a standard head and torso simulator, investigating different positions of the microphones and of the sound source and employing two different types of microphones. Finally, the HRTFs of five real subjects are measured and compared with the ones measured by the microphones in the ear of a standard mannequin.

On the efficient simulation of pass-by noise signals from railway wheels

The article presents an approach for calculating pass-by sound pressure radiated from railway wheels in the time domain using moving Green’s functions. The Green’s functions are obtained by using Finite Element (FE) and Boundary Element (BE) methods in the frequency domain, subsequent inverse Fourier transform, followed by convolution with a time series of rolling contact forces to obtain the pass-by time signals. However, traditional BE methods are computationally expensive due to the low structural damping of the wheel, necessitating a high frequency resolution.To overcome this issue, a modal approach is introduced in which the pass-by sound radiated by each wheel mode is calculated separately. This approach incorporates the dynamic response of the wheel in the time-domain processing and thus reduces the cost of the BE solution. A modal source signal is introduced to describe the excitation of each mode at each time step. The sound field radiated by unit modal amplitudes is calculated in BE and subsequently approximated by spherical harmonic (SH) equivalent sources, which allows for efficiently calculating acoustic transfer functions for varying relative positions of the wheel and a stationary receiver. Convolution of the source signal with the moving acoustic transfer function produces the pass-by pressure signal.The article investigates the directivity of the radiation from each mode and finds that most modes, including those with dominant radial deflection, radiate in mostly axial direction at high frequencies. Modes that dominate the pass-by pressure level are identified, both in frequency bands and with respect to the relative positioning of the wheel to the receiver. Finally, it is found that an SH expansion order of approximately 30 is required to satisfy the employed error measures, although lower orders may suffice for an auralisation of the signal.

Towards time-domain modelling of wheel/rail noise: Effect of the dynamic track model

Transient events in railway rolling noise, such as the characteristic impulsive noise at switches and crossings, can significantly contribute to the perceived annoyance, despite being difficult to detect in the standard frequency-domain methods to analyse rolling noise. Studying these transient effects and their perception requires predicting the noise in the time domain. While several time-domain approaches exist for predicting the dynamic interaction of wheel and rail, predicting the associated rolling noise with adequate accuracy is computationally costly. The lack of a model for transient noise and the need for studying its perception was recently identified. Aiming for a comprehensive time-domain radiation model that includes the wheel and track contributions to rolling noise, this work focuses on the track radiation. The modelling approach taken here is based on a 2.5D formulation for the acoustic radiation and moving Green’s functions in the air. The computational cost, which lies mainly in the 2.5D BE calculations, is addressed by pre-calculating acoustic transfer functions. These transfer functions can be combined with different dynamic track models. Different dynamic track models in turn affect radiated sound field in different ways. Here, the sound fields produced by six different track models are compared, including different support types and analytical and numerical rail models. Several descriptors of the sound field are analysed. In terms of the radiated sound power and radiation efficiency, modelling the rail as a simple beam leads to similar results as elaborate numerical models up to about 5 kHz. In terms of the track-side sound pressure, simple beam models can provide similar results only up to 2.5 kHz. Euler-Bernoulli (E-B) beams seem unfit for time-domain predictions of the radiated noise as they over-estimate the bending wave speed at high frequencies. The results also show that the standard track decay rate (TDR) and the decay of acoustic sound pressure along the track are comparable.

Impedance models for single and two degree of freedom linings with an improved data base and local non-linearity

Previously developed predictive models for impedance of single-degree-of-freedom and two-degree-of-freedom acoustic linings driven by a broad band acoustic source are reexamined. Two issues are addressed, the first being improvement of the conventional perforate face sheet impedance model. Data correlations based on flow bench measurements of steady flow pressure drop are reevaluated with emphasis on low flow velocity to improve the consistency of the prediction of linear resistance. In addition, for two-degree-of-freedom linings, face sheet mass reactance is modified to account for the presence of the septum. The second issue addresses the implication that for a non-linear lining, with impedance a function of the local sound pressure level, the installed performance of the lining depends on the local impedance, as opposed to impedance based on the source sound pressure level. This is investigated in the benchmarking of the impedance models by comparison of the acoustic transfer function predicted by a propagation code with the imbedded impedance model and transfer function measurements made in a grazing flow duct test facility. The propagation code is extended to make the non-linear behavior of the lining model dependent on the local acoustic spectrum, introducing an additional level of non-linearity and an iterative application of the propagation code. A principal conclusion is that with no grazing flow both the lining model and grazing flow duct transfer function measurements show a significant effect of local variation of the acoustic spectrum. With increasing grazing flow Mach number, this effect is reduced and effectively disappears at the highest Mach number. With increasing grazing flow Mach number the grazing flow contribution to face sheet resistance dominates and tends to mask the non-linear behavior of the component of resistance not related to grazing flow.

Sound zone control with fixed acoustic contrast and simultaneous tracking of acoustic transfer functions

As environmental changes are inevitable, online algorithms that can track the variation of acoustic transfer functions are preferred in sound zone control (SZC) systems. In this paper, it is found that for the time domain SZC, the nonuniqueness problem caused by the coupling in multichannel transfer function modeling can be solved with time-varying control filters. To keep a stable acoustic contrast (AC) performance irrespective of environmental changes and also avoid the extreme distortion introduced by maximizing the AC in the time domain, the objective of maintaining a desired level of AC is used and an adaptive control algorithm is developed. The simulations validate that the proposed method tracks the environmental changes and adapts the control filters to give a stable AC performance.

Neural acoustic fields

We present a way to compactly represent acoustic transfer functions using a small, yet flexible, parametric representation. We show that we can use a neural network as a “soft” table lookup and train it to produce the value of transfer functions at arbitrary points in space and time. Doing so allows us to interpolate and produce unseen data, and to represent acoustic environments using a remarkably compact representation. Due to this representation being differentiable, this opens up multiple opportunities to employ such models within more sophisticated audio processing systems.

Model based spectral feature analysis in reverberant acoustic fields

The spectral features of a reverberant acoustic field that can lead to improved source localization methods are investigated. Of particular interest are identification of deterministic and probabilistic features that characterize the environment and models of the acoustic transfer function that generate such features. For example, models that predict Schroeder’s invariant standard deviation in the pressure response at source-receiver distances where the direct sound approaches the reverberant field energy are proposed. Models examined include non-stationary Gaussian processes for the acoustic reverberant components and all-pass parametric models of the acoustic impulse response.

HRTFs Measurement Based on Periodic Sequences Robust towards Nonlinearities in Automotive Audio.

The head related transfer functions (HRTFs) represent the acoustic path transfer functions between sound sources in 3D space and the listener's ear. They are used to create immersive audio scenarios or to subjectively evaluate sound systems according to a human-centric point of view. Cars are nowadays the most popular audio listening environment and the use of HRTFs in automotive audio has recently attracted the attention of researchers. In this context, the paper proposes a measurement method for HRTFs based on perfect or orthogonal periodic sequences. The proposed measurement method ensures robustness towards the nonlinearities that may affect the measurement system. The experimental results considering both an emulated scenario and real measurements in a controlled environment illustrate the effectiveness of the approach and compare the proposed method with other popular approaches.

A Study on the Noise Optimization through the Analysis of Electric Vehicle Noise Paths

Since an internal combustion engine is not required for electric vehicle, the electric vehicle's noise is much lower than that of conventional internal combustion engine based vehicle. However, a road noise and wind noise that used to be masked by engine noise became the critical noise factors. Moreover, the electric vehicle generates a specific current conversion noise and motor high frequency noise that provides an unpleasant sound environment for drivers and passengers. In this study, therefore, the noise path of the electric vehicle was identified through Power Based Noise Reduction (PBNR) and Acoustic Transfer Function (ATF) tests. As a result of analyzing the noise path, it was confirmed that the rear side of vehicle was weak in terms of noise. As a countermeasure against this, it was confirmed that interior noise level could be improved by reinforcing the luggage side.

Accurate Prediction of Measured Microwave-Induced Thermoacoustic Signals via Multiphysics Simulations Augmented With an Acoustic Detection System Transfer Function

Accurate Prediction of Measured Microwave-Induced Thermoacoustic Signals via Multiphysics Simulations Augmented With an Acoustic Detection System Transfer Function

Improved Speech Spatial Covariance Matrix Estimation for Online Multi-Microphone Speech Enhancement.

Online multi-microphone speech enhancement aims to extract target speech from multiple noisy inputs by exploiting the spatial information as well as the spectro-temporal characteristics with low latency. Acoustic parameters such as the acoustic transfer function and speech and noise spatial covariance matrices (SCMs) should be estimated in a causal manner to enable the online estimation of the clean speech spectra. In this paper, we propose an improved estimator for the speech SCM, which can be parameterized with the speech power spectral density (PSD) and relative transfer function (RTF). Specifically, we adopt the temporal cepstrum smoothing (TCS) scheme to estimate the speech PSD, which is conventionally estimated with temporal smoothing. Furthermore, we propose a novel RTF estimator based on a time difference of arrival (TDoA) estimate obtained by the cross-correlation method. Furthermore, we propose refining the initial estimate of speech SCM by utilizing the estimates for the clean speech spectrum and clean speech power spectrum. The proposed approach showed superior performance in terms of the perceptual evaluation of speech quality (PESQ) scores, extended short-time objective intelligibility (eSTOI), and scale-invariant signal-to-distortion ratio (SISDR) in our experiments on the CHiME-4 database.

Structural Characteristics and Sound Absorption Properties of Waste Hemp Fiber

In order to realize high-efficiency and high-value recycling of waste hemp fibers, the macromolecular structure, the supramolecular structure, and the morphological structure of waste hemp fibers were investigated by using Fourier transform infrared spectroscopy, X-ray diffractometry, upright metallurgical microscopy, and scanning electron microscopy. According to its structural characteristics, the sound-absorbing mechanism of waste hemp fiber was analyzed, and the reason for the good sound-absorbing performance of waste hemp fiber was clarified. The acoustic impedance transfer function test was used to analyze and compare the sound-absorbing performance of waste hemp fiber and several other fiber aggregates that could be used in the field of sound-absorbing, and the sound-absorbing performance of a waste hemp fiber composite material was tested. The research revealed that: the sequence of sound-absorbing performance of several fiber aggregates was cotton fiber, waste hemp fiber, wool fiber, and polyester fiber; that waste hemp fiber had excellent high-frequency sound-absorbing performance, with a maximum sound absorption coefficient of 0.95; and that the maximum sound absorption coefficient of the waste hemp fiber composite reached 0.93. Therefore, the waste hemp fiber has excellent sound-absorbing properties and has high application value in the field of sound absorption.

Radiation modes and loudspeaker arrays for close-listening: Experimental verification

In personal audio systems, the loudspeaker array for enhancing the near field is designed based on the theory of generalized radiation modes. These modes are formulated as a generalized eigenvalue problem associated with acoustic transfer functions on the surface of the loudspeaker array. The eigenvectors, i.e., the modal shapes, represent combinations of the amplitude and polarity of individual loudspeakers. The eigenvalues indicate the reactive-to-active ratio of the acoustic power generated by the loudspeaker array. Hence, the loudspeaker array is designed according to the eigenvector with the largest eigenvalue to maximize the reactive-to-active ratio. In this study, a planar array consisting of nine loudspeakers is constructed, and the acoustic radiation characteristics are experimentally investigated.

Structural characteristics and sound absorption properties of different kinds of waste feather fibers

There are millions of tonnes of waste feathers every year from the booming poultry industry. To rationalize the utilization of waste feather resources, waste chicken feather fibers, waste duck feather fibers, and waste goose feather fibers were used as reinforcement materials, and polybutylene succinate was used as matrix materials to prepare sound absorbing composite materials. The acoustic impedance transfer function method was used to test the sound absorption performance of the sound absorbing composite materials with different feather fibers. The results showed that the sound absorbing composite materials with waste duck fibers had the best sound absorption performance. Fourier transform infrared spectrometer, X-ray diffraction, and scanning electron microscope were used to analyze the macromolecular structure, aggregation structure, and morphological structure of different kinds of waste feather fibers. According to the structure, the mechanism of sound absorption was analyzed, and the reason why the fibers of different kinds of waste feathers (chicken feather, duck feather and goose feather) had good sound absorption performance was clarified. It was clear that this unique structure endowed it with the characteristics of light weight and good sound absorption. So the waste feather fibers have high application value in the field of sound absorption.

Wideband absorbance for the assessment of pressure equalizing tubes patency in children.

To analyze the feasibility of using wideband absorbance to verify the patency of pressure equalizing tubes (PETs) in clinical practice and to present the response pattern of this measure for ears with patent PET. This observational case-control type study evaluated 48 ears of 30 children with severe or profound hearing loss, aged 10-44 months, of both sexes. The subjects were subdivided into two groups: 24 ears with Sheppard type PET (experimental group - EG) and 24 ears with normal middle ear (control group - CG), paired with the EG, according to age, sex, and ear evaluated. To obtain the wideband absorbance, a Middle-Ear Power Analyzer, version 5.0 (Mimosa Acoustics), was used, and absorbance values for pure tone and chirp stimuli were analyzed. There was no influence of ear (right or left) on the measurements obtained. The EG showed higher absorbance values at low frequencies. Although the two stimuli made it possible to identify the difference in acoustic transfer function between the groups studied, compared to pure tone, the chirp stimulus allowed identification of differences in a higher number of frequencies. Ears with a patent PET present an acoustic transfer pattern that differs from that obtained for normal middle ears, with a higher absorbance at low frequencies. Both pure tone and chirp stimuli can be used to identify such differences, nevertheless, the use of chirp stimulus is recommended, since it allows differentiation over a wider frequency range.

Dual Transfer Function Approach to Analyze Low Frequency Brake Noise without Comprehending Friction Behavior in Advance

<div class="section abstract"><div class="htmlview paragraph">Analyzing low frequency brake noise (< 300Hz) has been challenging due to the difficulty associated with calculating dynamic friction behavior and its multiple structure-borne noise transfer paths. In theory, it is possible to simulate sound pressure level inside the cabin by calculating a transfer function between friction excitation, which is on the interface between rotor and pads, and cabin acoustic response, and by multiplying dynamic friction force at the rotor-pad interface to that transfer function. However, calculating the dynamic friction forces when brake noise occurs has been one of the most challenging research topics in the brake community. This paper describes a novel concept to simulate sound pressure level inside the cabin without knowing the dynamic friction forces at the rotor-pad interface in advance. It becomes possible by dividing the transfer function into two separate steps: between the dynamic friction excitation at the rotor-pads and acceleration on caliper, and between the dynamic friction excitation at the rotor-pads and pressure response inside the cabin. The acoustic transfer function and the acceleration transfer function cancel out the need of knowing the friction excitation forces. The acceleration on the caliper is what is needed to calculate the sound pressure level along with those two transfer functions, and it is straightforward to collect/calculate the caliper acceleration than calculating/measuring the dynamic friction forces at the rotor-pads interface. Assessing the risk of low frequency brake noise based on actual acoustic response rather than indirect indicators like vibration or instability becomes a reality using this novel approach. The method has been proven that it captures the brake noise below 300Hz well when the noise is relatively pure-tone and quasi-transient.</div></div>

Robust single- and multi-loudspeaker least-squares-based equalization for hearing devices

To improve the sound quality of hearing devices, equalization filters can be used to achieve acoustic transparency, i.e., listening with the device in the ear is perceptually similar to the open ear. The equalization filter needs to ensure that the superposition of the equalized signal played by the device and the signal leaking through the device into the ear canal matches a processed version of the signal reaching the eardrum of the open ear. Depending on the processing delay of the hearing device, comb-filtering artifacts can occur due to this superposition, which may degrade the perceived sound quality. In this paper, we propose a unified least-squares-based procedure to design single- and multi-loudspeaker equalization filters for hearing devices aimed at achieving acoustic transparency. To account for non-minimum phase components, we utilize a so-called group delay compensation. To reduce comb-filtering artifacts, we propose to use a frequency-dependent regularization. Experimental results using measured acoustic transfer functions from a multi-loudspeaker earpiece show that the proposed equalization filter design procedure results in robust acoustic transparency and reduces the impact of comb-filtering artifacts. A comparison between single- and multi-loudspeaker equalization shows that for both cases a robust equalization performance can be achieved for different desired open ear transfer functions.