bluuebunny/crossref_metadata_2025 huggingface dataset:
Combination of gated recurrent unit and Network in Network for underwater acoustic target recognition
Authors: Yang Shuang , Zeng Xiangyang
Published: September 2021

Underwater acoustic target recognition is an important part of underwater acoustic signal processing and an important technical support for underwater acoustic information acquisition and underwater acoustic information confrontation. Taking into account that the gated recurrent unit
(GRU) has an internal feedback mechanism that can reflect the temporal correlation of underwater acoustic target features, a model with gated recurrent unit and Network in Network (NIN) is proposed to recognize underwater acoustic targets in this paper. The proposed model introduces NIN to
compress the hidden states of GRU while retaining the original timing characteristics of underwater acoustic target features. The higher recognition rate and faster calculation speed of the proposed model are demonstrated with experiments for raw underwater acoustic signals comparing with
the multi-layer stacked GRU model.
Design and optimization of acoustic liners with a shear grazing flow: OPAL software platform description
Authors: Simon Frank , Roncen R. , Vuillemin P. , Klotz P. , Méry Fabien , Piot E.
Published: September 2021

In the context of aircraft noise reduction in varied applications where a cold or hot shear grazing flow is present (i.e., engine nacelle, combustion chamber, jet pump, landing gear), improved acoustic liner solutions are being sought. This is particularly true in the low-frequency
regime, where space constraints limit the efficiency of conventional liner technology. Therefore, liner design must take into account the dimensional and phenomenological characteristics of constituent materials, assembly specifications and industrial requirements involving multiphysical phenomena.
To perform the single/multi-objective optimization of complex meta-surface liner candidates, a software platform coined OPAL (OPtimisation of Acoustic Liners) was developed. Its first goal is to allow the user to assemble a large panel of parallel/serial elementary acoustic layers along a
given duct. Then, the physical properties of this liner can be optimized, relatively to weighted objectives, for a given flow and frequency range: impedance target, maximum absorption coefficient or transmission loss with a total sample size and weight... The presentation will focus on the
different elementary bricks and assembly of a problem (from 0D analytical coarse designs in order to reduce the parameter space, up to 2D plan or axisymmetric high-order Discontinuous Galerkin simulations of the Linearized Euler Equations).
Sound absorption based on Micro-perforated panels and Acoustic Black Hole principle
Authors: Zhang Xiaoqi , Cheng Li
Published: September 2021

Acoustic black holes (ABHs) have been so far investigated mainly for bending wave ma-nipulation in mechanical structures such as beams or plates. The investigations on ABHs for sound wave manipulation, referred to as Sonic black holes (SBHs) are scarce. Existing SBH structure for sound
reduction in air is typically formed by putting a set of rings inside a duct wall with decreasing inner radius according to a power law. As such, the structure is very complex and difficult to be practically realized, which hampers the practical application of SBHs for sound reduction. This
study explores the possibilities of achieving SBH effects using other types of structural configurations. In particular, micro-perforated panels are proposed to be introduced into the conventional SBH structure, and the simulation results show that the new formed SBH structure is simpler in
configuration in terms of number of rings and more efficient in terms of sound energy trapping and dissipation.
Visualization of magnetic field corresponding to acoustic signal and estimation of magnetic source based on symmetry of magnetic field distribution
Authors: Kurosawa Takuto , Ishizuka Eri , Oikawa Yasuhiro , Konno Minoru , Asakawa Masatoshi , Suzuki Yuya
Published: September 2021

A magnetic field corresponding to an acoustic signal is generated from an antenna, and by using a coil, can be again converted to an acoustic signal. It is possible to estimate where the invisible antenna is with the distribution of the received signal. The estimation is applied to
a maintenance of a gas pipe on the situation that the distance from the entrance to a maintenance area is known, but piping route isn't. It is possible to identify maintenance areas of a gas pipe by inserting the antenna to it. The estimation has been done by listening to the received signal
manually. However, it is difficult for people to identify accurate point because the difference in the volume for each places is subtle. To solve this problem, we visualized the distribution of the received signal, and estimated the magnetic field with only the acoustic signal. Then, we proposed
a method to calculate where the invisible antenna is automatically by using symmetry of the distribution of the received signal.
Numerical study in sound absorption ability of curtain in random incidence condition
Authors: Cai Zenong , Li Xianhui , Gai Xiaoling , Xing Tuo , Wang Fang , Guan Xiwen
Published: September 2021

Woven fabric can provide variety application scenarios in acoustic field as flexible and light features. Folded curtain can be made from fabric, which is a good application example of woven fabric in noise control as sound adjuster in multi-function halls. Many geometric parameters can affect the sound absorption ability of folded curtain, such as folding shape, folding depth, the average distance of air cavity and folding period, etc. However, in random incidence condition, the relationship of geometry parameters and sound absorption ability is not clear in previous works. To obtain this relationship, Finite Element Method is used in this work. Because of the different folded shape, the contribution fractions of different angles are changed by the different geometry parameters. A series of 3D models is established with different geometric conditions. Different angles of incidence plain sound waves are introduced in 3D models. Numerical results show the detailed contribution fractions of different angles. This paper shows that previous model can provide reliable predicted results for flat curtain.
Design of noise barriers for the mitigation of construction noise
Authors: Lee Heow Pueh
Published: September 2021

Noise pollution is a major problem in many major cities in particular a small island state like Singapore with residential buildings very close to the major trunk roads and expressways. The problem is aggravated by the ongoing city redevelopment and construction of new mass rapid transit
lines. Construction noise is therefore a common theme of public complaints and therefore there is an increased interest in the development of more effective mitigation measure for construction noise. In this work, a Flat-tip jagged-edge profile was investigated and applied on the edge of a
cantilever (slanted up for 45 degrees, facing the noise source) which was mounted at the top of a passive noise barrier. Besides the numerical simulations, the full sized prototypes were also experimentally tested on a construction sites with noise generated by a boring machine. Both numerical
simulations and experimental results showed that this barrier with a slanted Flat-tip jagged cantilever would perform better than the traditional barrier having a Straight-edge cantilever of same height, with a maximum additional attenuation of 5.0 dBA experimentally obtained. The barrier
with slanted Flat-tip jagged cantilever could also extend the shadow zone behind the barrier to higher levels of the building.
Effects of annular acoustic black holes on sound radiated by cylindrical shells
Authors: Guasch Oriol , Deng Jie
Published: September 2021

While most acoustic black hole (ABH) designs are intended to reduce vibrations in beams and plates, annular ABHs have been recently proposed for cylindrical shells. The key to achieve the ABH effect in a structure consists in embedding an indentation on it such that it slows down incident
waves and concentrates their energy at the center of the ABH. There, it can be typically dissipated by means of a viscoelastic layer. Many studies exist on the vibration of structures with ABH indentations but only a few address the topic of sound radiation. In this work, we evaluate the impact
that an annular ABH has on the sound radiated by a baffled cylindrical shell. The vibration of the cylinder is computed using Gaussian basis functions in the Rayleigh-Ritz method. Once determined the surface velocity of the ABH cylinder, a Green's function approach is employed to obtain its
surface acoustic pressure and then the sound power level, radiation efficiency and supersonic intensity. The dependency of the latter on the ranges determined by the ring and critical frequencies is analyzed for the case of a thick acoustic shell. Beyond the critical frequency, supersonic
flexural waves entering the ABH become subsonic, substantially reducing the radiation efficiency and therefore, the emitted sound. Further reduction is achieved once passed the ring frequency.
ATEFA - A first German approach on UAM community noise and air-taxi certification
Authors: Bauer Michael , Redmann Daniel , Weilandt Lis
Published: September 2021

Urban air mobility (UAM) includes larger air taxis, driven by multiple distributed propellers or fans, installed in a fixed configuration or as tilted wings/engines. These novel electric air vehicles will always generate tonal and broadband noise, in some cases with components from
a specific installation situation. In any case, noise will propagate to the ground, into high populated areas of large cities or into their urban environment, individually depending on the operational situation of air taxi use. Some of the populated areas, where no significant noise from air
traffic has been observed so far, will be exposed to this new type of aircraft noise. ATEFA, as the first German national funded research project on UAM community noise, aims to provide first answers. Three selected air taxi concepts, strongly differing acoustically from each other, will be
technically described and their noise emissions will be modeled and predicted. Air taxi operations will be simulated by generic traffic scenarios in a selected area of southern Germany, and community noise near vertiports, but also "en-route" along the flight paths, will be computed.
Beside this, noise certification aspects will be assessed regarding metrics and procedures and compared to a light low-noise helicopter as reference aircraft.
An adjustable bearing seat stiffness element for targeted vibration influencing
Authors: Sturm Carolin , Lindenmann Andreas , Gwosch Thomas , Matthiesen Sven
Published: September 2021

In order to be able to influence the dynamic system behavior in a targeted manner, parameters such as stiffness in the technical system must be adjustable. In high-speed powertrains, the stiffness of the bearing seat, in particular, has an influence on the dynamic characteristics. As
part of our research, we developed an adjustable bearing seat stiffness element. The focus of research was on an adjustable, scalable element with a small design space and the same properties over the perimeter. We characterized it statically with the help of a universal testing machine and
dynamically using a shaker system. The results are compared with theoretical approaches. The results show that the stiffness is almost linearly adjustable in the load range of 0-100N. The results indicate that the developed element can be used to adjust desired stiffness and thus to influence
vibrations in a targeted manner. The findings can be used in the design of high-speed powertrains e.g. in serial products or test benches.
Comparison of two community noise models applied to a NASA urban air mobility concept vehicle
Authors: Page Juliet , Rizzi Stephen A. , Cheng Rui
Published: September 2021

Predictions of community noise exposure from the NASA urban air mobility (UAM) concept vehicles have been conducted for representative operations using the FAA Aviation Environmental Design Tool (AEDT) in order to demonstrate modeling tool interoperability and assess applicability,
capabilities and limitations of integrated noise modeling tools. To both quantify limitations and highlight other capabilities, a comparative analysis is performed using a time simulation method, in particular, using the Volpe Advanced Acoustic Model (AAM). Starting with the same source noise
model, the 3D directivity of a UAM concept vehicle is predicted in terms of aeroacoustic pressure time histories at a sphere of observers near the vehicle. In addition to distilling those data to a set of noise-power-distance data for input to AEDT, the data are processed preserving directivity,
into narrowband, one-twelfth and one-third octave bands for input to AAM. Results from AEDT and AAM modeling are provided for a variety of metrics to demonstrate the effect that source noise and propagation modeling fidelity have on predicted results at receptors over a study area.
Comparison of quadrature and regression based generalized polynomial chaos expansions for structural acoustics
Authors: Walters Gage , Wixom Andrew , Martinelli Sheri
Published: September 2021

This work performs a direct comparison between generalized polynomial chaos (GPC) expansion techniques applied to structural acoustic problems. Broadly, the GPC techniques are grouped in two categories: , where the stochastic sampling is predetermined according to a quadrature rule;
and , where an arbitrary selection of points is used as long as they are a representative sample of the random input. As a baseline comparison, Monte Carlo type simulations are also performed although they take many more sampling points. The test problems considered include both canonical
and more applied cases that exemplify the features and types of calculations commonly arising in vibrations and acoustics. A range of different numbers of random input variables are considered. The primary point of comparison between the methods is the number of sampling points they require
to generate an accurate GPC expansion. This is due to the general consideration that the most expensive part of a GPC analysis is evaluating the deterministic problem of interest; thus the method with the fewest sampling points will often be the fastest. Accuracy of each GPC expansion is judged
using several metrics including basic statistical moments as well as features of the actual reconstructed probability density function.
Case study - lesson plan for noise control engineering concepts for use in ABET accredited engineering programs
Authors: Wang Lily , Beamer Bryan , Moore Keegan J. , Krainc Katie
Published: September 2021

ABET accreditation is an internationally recognized system ensuring consistency and quality in engineering education programs. As a part of ABET accreditation, there is no set requirement for any general engineering program to include noise control engineering concepts in their curricula.
However, one of the seven student outcomes that each ABET accredited engineering program must document is their students' "ability to apply engineering design to produce solutions that meet specified needs with consideration of public health, safety, and welfare..." Controlling noise
is a fundamental strategy for protecting workers from occupational noise and the public from the harmful effects of environmental noise. In this presentation, a case study is presented which focuses on the development and execution of a noise control lesson plan designed to meet ABET requirements.
The lesson plan not only promotes the understanding and practice of noise control engineering techniques but also is designed to help engineering programs demonstrate ABET student outcomes related to consideration of safety and health.
Pilot studies of noise annoyance in relation to time, amplitude and frequency characteristics of sound
Authors: Radosz Jan
Published: September 2021

Noise is any unwanted sound that may be disruptive or harmful to health or increase the risk of an accident at work. Noise as a stressor can contribute to the development of various types of diseases, cause distraction, make work difficult and reduce its efficiency. Aim of the pilot
studies was to asses noise annoyance in relation to time, amplitude and frequency characteristics of sound in typical office environment. The Vienna Test System was used for this purpose. Virtual office acoustic environments were developed with different psychoacoustic parameters, but with
a constant A-weighted sound pressure level of 55 dB - environment with conversations, environment with office equipment (computers, printers, telephones), environment D with all office noise sources together. The reference environment was a quiet office room with no additional noise sources.
Recorded real noise sources were transferred to a virtual 3D sound environment and converted into binaural sound, which was then played back on headphones. During the exposure to each of the acoustic environments, the subjects performed the ALS test (work performance series) and then assessed
the given environment using a questionnaire. The tested acoustic environments were assessed in the range from not at all annoying to very annoying. On average, environments with office noise were rated as moderately annoying. However, subjective feelings of the respondents were not reflected
in the results of psychological tests.
Vibration of a stiffened pipe filled with a bubbly liquid: analysis of resonance frequencies in function of bubble fraction
Authors: Serbout Sanae , Maxit Laurent , Michel Frédéric
Published: September 2021

The characterization of the presence of bubbles in industrial fluid circuits may be extremely important for many safety issuses. It is well known that the acoustic properties of liquids can be drastically modified by a small amount of gaz content in the liquid. At sufficiently low frequencies,
the speed of sound depends primarily on the gas volume fraction. The variation of the gas fraction may then induce some variations in the vibroacoustic behavior of the pipe transporting the liquid. Analysis of the pipe vibrations can then help in the monitoring of the bubble presence. In such
a context, the aim of this study is to show how the the presence of bubbles in the liquid could affect the resonance frequencies of the pipe. A numerical vibroacoustical model has been developed to predict the vibroacoustical behavior of a stiffened cylindrical shell filled with a bubbly liquid
exhibiting low frequency resonances. The model, experimentally verified with a well-characterized bubbly liquid, is then used to analyse the frequency shifts of the shell resonances in function of the bubble. Keywords : pipe, heavy fluid, numerical modelling, circumferential admittance approach,
cylindrical shell, resonance frequency, void fraction
An explicit time-domain FEM for acoustic simulation in rooms with frequency-dependent impedance boundary: Comparison of performance in 2D simulation with frequency-domain FEM
Authors: Yoshida Takumi , Okuzono Takeshi , Sugimoto Yui , Sakagami Kimihiro
Published: September 2021

Accurate boundary modelings that address the frequency-dependent sound absorption characteristics of various sound absorbers are crucial for wave-based room acoustic simulation. In time-domain simulations, however, a computationally demanding convolution appears in frequency-dependent
impedance boundary conditions. The present paper proposes a room acoustic solver with a fourth-order accurate explicit TD-FEM, incorporating a frequency-dependent absorbing boundary condition efficiently using a recursive convolution method, namely the auxiliary differential equation (ADE)
method. Its performance against the fourth-order accurate frequency-domain FEM is examined via 2D real-scale room acoustic problems, solving a sound propagation in an office room up to 4.5 kHz. Firstly, we describe briefly the formulation of the proposed room acoustics solver based on the
explicit TD-FEM. Then, the discretization error property of the proposed method is evaluated via an impedance tube problem, including a frequency-dependent impedance boundary of porous sound absorber. Finally, the accuracy and efficiency of the proposed method are demonstrated with the comparison
of frequency-domain FEM solver, which uses a sparse direct solver for the solution of the linear system at each frequency. Results showed the proposed method can perform an acoustic simulation with significantly low computational costs compared to the frequency-domain solver while keeping
an acceptable level of accuracy.
Sound Field Projection System using Optical See-Through Head Mounted Display
Authors: Inoue Atsuto , Teraoka Wataru , Oikawa Yasuhiro , Satou Takahiro , Iwane Yasuyuki , Kobayashi Masahito
Published: September 2021

There are various ways to grasp the spatial and temporal structures of sound field. Sound field visualization is an effective technique to understand spatial sound information. For example, acoustical holography, optical methods, and beam-forming have been proposed and studied. In recent
years, augmented reality (AR) technology has rapidly developed and is now more familiar. Many sensors, display devices, and ICT technologies have been implemented in AR equipment, which enable interaction between real and virtual worlds. In this paper, we propose an AR display system, which
displays the results obtained by the beam-forming method. The system consists of 16ch microphone array, real-time sound field visualization system and optical see-through head mounted display (OST-HMD). Real-time sound field visualization system analyses sound signals recorded by 16ch microphone
array by beam-forming method. Processed sound pressures data are sent to OST-HMD by using transmission control protocol (TCP), and colormap is projected on real world. Settings property of real-time sound field visualization system can be changed by using virtual user interface (UI) and TCP.
In addition, multi-users can experience the system by sharing sound pressures and settings property data. Using this system, users wearing OST-HMD can observe sound field information intuitively.
A constrained optimal hear-through filter design approach for earphones
Authors: Zhuang Yongjie , Liu Yangfan
Published: September 2021

The sound from environment will be altered after it transmits through headphones to the ear canal. A hear-though filter can be designed and implemented in the headphones to create a more natural hearing experience, i.e., offer a transparent mode for headphones. The design of hear-through
filter is also required in some other applications, e.g., augmented reality audio. In this paper, a constrained hear-through filter design approach is proposed. It is firstly shown that the hear-through filter design problem can be formulated in a similar form to active noise control filter
design in the frequency domain. One advantage of this design approach is that multiple practical constraints can be applied conveniently by formulating a constrained optimization problem. Then the constrained optimization problem for hear-through filter design is reformulated as cone programming
problem which can be solved efficiently. The proposed design approach can also specify the desired delay of reproduced sound. The designed filter can be directly implemented in an active noise control system in the headphone such that the requirement for extra electronic components can be
minimal.
Comparison of noise generated from simplex and duplex configurations of drum brake using non-linear vibro-acoustic models
Authors: Yella Akash , Sundar Sriram
Published: September 2021

The drum brakes used on the rear wheels of automobiles have various configurations. These contribute to the differences in kinematic (geometry) and dynamic (contact, friction) aspects, eventually leading to significantly different vibration and acoustic response. This work attempts
to estimate the difference in the vibro-acoustic noise generated by the drum brake's simplex and duplex variants using a combination of non-linear analytical vibration models and a numerical acoustic model. Four degrees-of-freedom lumped parameter models developed for the simplex and the duplex
configurations with conformal contact predict the contact and reaction forces during braking. These forces act as the sources for the finite element based acoustic models developed for the two configurations to obtain the sound pressure to force transfer functions. The sound pressure levels
are estimated by the product of the predicted forces with the respective transfer functions in the frequency domain. The sound pressure levels of the simplex and duplex drum brakes are quantitatively compared under different braking conditions, and the results are presented. It is expected
that this vibro-acoustic analysis will help in designing quieter drum brakes.
A FEM/Kirchhoff-Helmholtz integral model for noise diffractors on low height noise barriers
Authors: Wijnant Ysbrand , Rochat Judith L. , Willems Bart , Schwanen Wout
Published: September 2021

So-called noise diffractors are a novel way to reduce traffic noise. As opposed to blocking or absorbing noise, diffractors bend noise in an upward direction, creating a shadow zone of reduced noise levels behind the diffractor. The diffraction is most effectively induced by quarter-wavelength
resonators. The resonators can be placed in the ground but can also be mounted on top of a (low height) noise barrier, which provides additional reduction. In this paper, we describe a finite element/Helmholtz integral model for a diffractor mounted on a low height noise barrier. The finite
element model is used to calculate the scattered acoustic field in the proximity of the diffractor for a noise source sufficiently far away from the diffractor. The acoustic pressure and particle velocity on the outer boundary of the finite element domain are subsequently used in the Kirchhoff-Helmholtz
integral formulation to evaluate the acoustic field in the far field. The major benefit of this approach is a large reduction of the model size and reduced calculation times. This allows us to assess the reduction values at different barrier heights, larger distance from source to diffractor
and larger distances from diffractor to evaluation points, with an example shown for highway traffic noise.
Vibrational Monitoring of Nested Planetary Geartrain with Unground Pinion
Authors: Feng Jianxiong , Liu Yangfan , Li Kai Ming
Published: September 2021

The nested planetary gear train, which has two integrated single-stage planetary gearsets, is one of the newly developed compound gear train that has been successfully applied to the automobile transmissions. In the current study, a certain type of gear fault in the nested gear train,
ungrounded pinion, is investigated using a non-destructive approach monitoring its vibration levels. A novel experimental test stand with open and vertical setup has been designed to collect the vibrational data by mounting the accelerometer directly to the gear clutches. Each of the two layers
of the compound gear was tested separately. The measured vibrational data were processed with several signal processing techniques, which includes (a) frequency spectrum analysis, (b) time synchronous averaging (TSA) and (c) modulation sideband analysis. The experimental results show that
the existence of the ungrounded pinion can be identified with the frequency spectrum analysis of the vibrational data. In addition, the modulation sidebands are also modeled using a modified version of the traditional technique of physical signal modeling. It is shown that the relative phase
of the planet and the meshing vibration strength changed by the unground gear is the critical factor for determining the modulation sideband behavior. In addition, the location of the ungrounded pinion can also be determined by the time history processed by TSA.
Development of experimental vibro-acoustic transfer function for a system with combined rolling-sliding motion
Authors: Shripad Kumar Milind Rewanand , Sundar Sriram
Published: September 2021

Combined rolling-sliding contact is present in popular non-linear systems such as cam-follower, gears, clutches, and brakes. These systems produce significant noise due to complex contact between the components during operation. The noise generated is a strong function of the contact
parameters and excitation to the system. The objective of this study is to develop a transfer function to quantify the vibro-acoustic noise for various contact conditions. Acceleration, reaction forces, and acoustic pressure measurements are made on a cam-follower setup with combined rolling-sliding
contact. Experiments are performed under different conditions of friction, lubrication, load, and speed. Contact forces are back-calculated using the kinematics. The transfer function relating the acoustic pressure to different forces is estimated. It is observed that the contact parameters
govern the transfer function and hence the vibro-acoustic systems. The developed transfer function is useful in designing better sub-systems with combined rolling-sliding contact to reduce noise exposure, as a direct technique to relate the contact parameters to the noise does not exist. This
study can be extended to other complex systems such as gears and clutches.
Sound Field Reconstruction in Rooms with Deep Generative Models
Authors: Karakonstantis Xenofon , Fernandez Grande Efren
Published: September 2021

The characterization of Room Impulse Responses (RIR) over an extended region in a room by means of measurements requires dense spatial with many microphones. This can often become intractable and time consuming in practice. Well established reconstruction methods such as plane wave
regression show that the sound field in a room can be reconstructed from sparsely distributed measurements. However, these reconstructions usually rely on assuming physical sparsity (i.e. few waves compose the sound field) or trait in the measured sound field, making the models less generalizable
and problem specific. In this paper we introduce a method to reconstruct a sound field in an enclosure with the use of a Generative Adversarial Network (GAN), which s new variants of the data distributions that it is trained upon. The goal of the proposed GAN model is to estimate the underlying
distribution of plane waves in any source free region, and map these distributions from a stochastic, latent representation. A GAN is trained on a large number of synthesized sound fields represented by a random wave field and then tested on both simulated and real data sets, of lightly damped
and reverberant rooms.
Acoustical behavior of loss-optimized involute gears
Authors: Sepp Sebastian , Goetz Joshua , Stahl Karsten
Published: September 2021

The progressing electrification of vehicle drive systems focuses more and more on efficient high-speed concepts. Increasing the motor speed leads to a higher power density of the electrified power train and thereby to an increased range for battery electric vehicles. The high rotational
speeds cause new challenges in designing gearboxes regarding the efficiency and the acoustical behavior. Most present gearings in conventional vehicles are designed with high tooth depths to ensure low noise excitation behavior combined with the best possible efficiency. By changing the gear
geometry to smaller tooth depths with higher pressure angles, it is possible to further decrease gear losses. However, the loss-optimized gear geometry must not jeopardize the beneficial acoustical behavior. In theoretical studies, the acoustical behavior of loss-optimized gears are investigated
and compared to gearings designed according to the state of the art. Design calculations of the excitations of all ideal gears without deviations are on similar levels. However, application of such gear geometries faces severe challenges because the sensitivity to manufacturing deviations
may be high. In this paper, simulation results and test results between low-NVH gears and loss-optimized gears are documented and analyzed.
A review of variable-impedance acoustic liner concepts developed at NASA
Authors: Jones Michael
Published: September 2021

This paper presents results attained in the NASA Langley Research Center test rigs using concepts for which the impedance varies over the surface of the liner. These liners are typically designed for significant sound absorption over a wide frequency range, but it is also possible to
tune the design to achieve increased absorption at selected frequencies. A brief review is provided regarding a number of variable-impedance concepts. The first is a modified version of a conventional two-layer liner, in which the embedded septum location and acoustic properties are different
for adjacent core chambers. Two concepts employ core chambers with different lengths, one with bent chambers to allow packaging within a limited volume, and the other with shared inlet ports to reduce the surface porosity. The last employs a perforated facesheet in which the hole diameter
and porosity are varied over the surface of the liner. Data acquired in the NASA normal incidence and grazing flow impedance tubes are used to demonstrate the capabilities of these concepts. Impedance prediction models are also presented for comparison with these measured data.
Virtual bass preprocessing and carrier frequency optimization for the parametric array loudspeaker
Authors: Tao Shengqi , Ren Jing , Shi Chuang
Published: September 2021

The parametric array loudspeaker (PAL) is a novel type of loudspeaker that can project a directional sound beam. It is usually used in creating personal sound zone and projecting private messages to a targeted audience. However, the PAL has a very poor low-frequency response due to
the inherent nonlinear acoustic principle generating sound from ultrasound in air. A psychoacoustic signal processing method known as the virtual bass (VB) has been proved to be an effective method to improve the bass quality of consumer electronics with miniature or flat loudspeaker unit.
This paper proposes the VB processing based on the phase vocoder (PV) for the bass enhancement of the PAL that adopts a vestigial sideband modulation method. The harmonics generated by the VB processing are presented in the partial sideband, while the audio input without the bass component
is embedded in the full sideband. A measure, namely the in-band peak flatness, is thereafter proposed in this paper to determine the optimal carrier frequency, given a practical uneven frequency response of the ultrasonic transducer. The subjective testing results validate that the proposed
VB processing together with the optimal carrier frequency can finally realize the improvement of bass sound quality of the PAL.
Analytical model of the diffuse sound transmission loss of finite double panel structures
Authors: Vazquez Torre Javier , Brunskog Jonas , Cutanda Henriquez Vicente
Published: September 2021

An analytical model for the forced sound transmission loss of finite single-leaf walls using a variational technique was previously developed and validated. As the double panel is one of the most used structures in building acoustics, the aim of this paper is to extend the analytical
model to consider double panel structures. Analytical formulas for the forced part of the airborne sound insulation of finite sized double panel structures are derived using a variational technique based on the integral-differential equation of the fluid loaded panels. The formulas are valid
in the entire audible frequency range. The results are compared to alternative analytical models and measurements, with reasonable agreement.
Power generator noise evaluation considering conversation audibility and improvement
Authors: Yoshida Junji , Nishimura Yoshiki , Uegaki Senta
Published: September 2021

Compact power generators are useful and convenient tools all over the world. The products are mainly set at around living space of human. Hence, the radiated noise should not disturb the human activities such as conversation. In this study, we then focused on the ease of conversation
as the power generator noise performance and attempted to improve the performance. We firstly carried out subjective evaluate tests using recorded generator noise samples and reproduced Japanese syllables to evaluate the performance quantitatively from sound pressure of power generator noise.
In the test, the participants answered the syllable they heard under the reproduced generator noise condition. And the correct answer rate of the presented syllable was calculated in each generator noise. The correct answer rate could be expressed well by using articulation index (AI) of each
generator noise. Subsequently, the noise reduction target level of a portable generator satisfying the rate at 80% was set in each frequency band considering the influence of each frequency band on AI. Noise countermeasure was carried out to intake and exhaust parts having large contribution
at the reduction target frequency bands. Finally, the noise could be decreased well and the AI cleared the target level.
Does the wall sound different? Variable acoustics in rehearsal rooms using small resonator structures in an acoustic panel.
Authors: Knöfel Björn , van Brummelen Paula , Behrens Tobias , Schirmer Hartmut
Published: September 2021

As the name already states, multipurpose rooms are often used from various people for different intentions like meetings or musical practicing. One example are musical rehearsal rooms, where the acoustic specifications have to meet the requirements of musicians playing different instrument
groups. To meet the desire for variable acoustics in a rehearsal room, musicians often like to adjust the room to there personal preferences, what is mostly done by adjusting the frequency dependent room decay curve (T60). Hence, a variable acoustic panel has been developed which consists
of several small adjustable resonator structures. In a closed state, the structure acts like a resonator. Although Helmholtz resonators are mostly used at low frequencies, the acoustic panel can address acoustic resonance absorption in the mid-frequency range between 500 Hz and 1.500 Hz. The
paper highlights especially the dimensioning of the resonators and its measurements in an impedance tube, a reverberation cabin and a reverberation room. Finally, the prototype of the acoustic panel has been analysed in different rehearsal rooms where musicians examine the panel and T60 differences
between the open and closed state of the panel were measured.
Acoustic study in a main avenue and its effects in classrooms and offices of a university in Mexico City
Authors: Javier Antonio , Kuri Bautista
Published: September 2021

This study presents the results of a detailed acoustic investigation, systematized and with adequate equipment to the current regulations, carried out in an avenue of intense vehicular traffic located in front of a recently built architectural complex, based on concrete, aluminum, glass,
and other materials, called the Postgraduate Unit, belonging to the National Autonomous University of Mexico. These measurements show that, in the initial design of the buildings, the most current knowledge about exterior-interior sound insulation through their facades was not considered.
The data collected and the interviews conducted reveal that the Sound Pressure Levels rise, altering the Interior Acoustic Comfort, necessary for the performance of daily academic, administrative and research activities, resulting in permanent inconveniences for users, in addition to the saturation
of areas, lack of adequate spaces and excessive unscheduled expenses. Paradoxically, empty spaces are observed in areas with high Sound Pressure Levels, which means that there is a certain level of architectural failure.
Active noise control without secondary path modeling: algorithm and implementation
Authors: Ren Xing , Zhang Hongwei
Published: September 2021

Active noise control (ANC) has been intensively studied for decades. The most classical ANC algorithm should be the filtered-x least mean square (FxLMS) algorithm, which needs the model of the secondary path to work. Thus, the residual error of the ANC system is closely related to the
preciseness of the secondary path model. In many applications, the secondary path is often time-varying. Therefore, off-line identification of the secondary path is not applicable. However, on-line identification often requires an additional white noise as a stimulating signal of the secondary
path, which will deteriorate the final noise reduction effect. This paper proposes an improved artificial bee colony (ABC) algorithm for ANC system, which does not require identification of the secondary path. In order to guarantee the convergence of the algorithm and accelerate the convergence
speed, this paper introduces a variable forgetting factor into the fitness function, and improves the traditional ABC algorithm by integrating LMS algorithm into the ABC algorithm. A single channel ANC system equipped with an FPGA hardware platform is set up in an anechoic chamber, and experiments
show that the proposed algorithm can produce a satisfactory noise reduction effect without modeling the secondary path.
Implementation of coherence-based-selection multi-channel wireless Active Noise Control in headphone
Authors: Shen Xiaoyi , Shi Dongyuan , Gan Woon-Seng , Peksi Santi
Published: September 2021

Active noise control (ANC) headphone is widely used to attenuate the noise around human' s ear. The microphone mounted on the conventional ANC headphones collected the mixed reference signals when more than one noise sources are often present in the surrounding. In this case, the uncorrelated
noise sources involved in the mixed reference usually deteriorate the noise reduction performance of the ANC headphones. To solve this problem, wireless microphones are proposed to install close to each potential noise source in the environment. The microphones pick up the clean reference
signals and transmit them to the ANC controller embedded in the headphones with time-advance wirelessly. Every reference signal selected by a coherence-based-selection algorithm is provided individual control filter in each ear. Each control filter updated by using a single clean reference
offers better noise reduction performance for ANC headphones. Furthermore, numerical simulations and real-time experiment results in this paper demonstrate the improvement of the proposed method compared with conventional ANC headphones.
Understanding the Effect of Geometric Forms on Indoor Soundscape Assessment: A Case Study in CSO Concert Halls in Ankara, Turkey
Authors: Erdoğu İlayda , Yılmazer Semiha
Published: September 2021

This study aims to compare the indoor soundscape of two concert halls with different geometric forms. The study included Presidential Symphony Orchestra (CSO) Concert Hall (CH) and CSO Grand Hall (GH) in Ankara, Turkey. CH was in shoebox form, and GH had vineyard form. Participants
consisted of undergraduate students of the Interior Architecture and Environmental Design Department of Bilkent University. Twenty females and twenty males were selected between the ages of 20-25. They were randomly divided into two groups as CH and GH. An online listening test with the same
music but different recordings of each hall was applied. Also, tests had the visuals of the relevant concert hall. The perceptual data was collected with the questionnaire from ISO/TS 12913 2 Method A. The results showed that the overall soundscape quality of GH was perceived as more positive
than CH. The surrounding sound in GH was more eventful and pleasant than CH.
Corn plants as temporary acoustic barrier to limit the effects of noise pollution
Authors: Iannace Gino , Puyana-Romero Virginia , Ciaburro Giuseppe
Published: September 2021

Corn is a cereal imported into Europe from the Americas and is used for human and animal feed, but there are also industrial uses such as the production of ethanol, as a fuel for heating homes or to produce starch. Corn grows in the summer in areas where there is water. Corn is grown
in many regions of the world and its production exceeds that of any other cereal in quantity. The corn plant can reach up to three meters in height, with a stem diameter of a few centimeters and with dense leaves longer than 30 cm and 10 cm wide. There are noisy activities where it is necessary
to attenuate the noise produced to limit the effects of noise pollution. Some activities use temporary barriers depending on the processing cycle adopted. If noisy work is carried out during the summer season, corn rows of adequate width can be used as an acoustic barrier. In this paper, the
possibility of using corn plants as an acoustic barrier is investigated. The acoustic measurements of the noise attenuation of corn rows of adequate width are described. Using a semi-spherical source placed on the ground, the acoustic attenuation due to the corn plants arranged in several
rows for different distances from the sound source to the receiver was measured.
Phononic crystal sandwich for broadband and low frequency acoustic insulation under diffuse field
Authors: Aberkane-Gauthier Natacha , Moleròn Miguel , Lecoq Damien , Lagarrigue Clément , Pézerat Charles , Romero-García Vincente
Published: September 2021

Light and thin structures exhibiting high sound insulation over a wide frequency range are a major industrial concern, especially in the transport and building sectors. Phononic crystals constitute promising solutions to solve this issue due to their particular dispersion properties.
In this work, we build a system consisting of a well-known sandwich panel comprising a soft elastic core layer hosting periodically arranged rigid inclusions. Diffuse field measurements show a huge improvement of the Transmission Loss compared to the system without inclusions. In fact, for
this kind of panel, the structured core enables Bragg band-gap opening for guided slow propagating waves leading to low frequency and broadband enhancement of the Transmission Loss. Using a 3cm-thick material we are able to improve the response from 300 Hz on (λ/38 in air). We then
develop a finite elements model to achieve a precise description and understanding of the problem. We also propose a numerical tool to analyze the system's band-structures from a vibroacoustic point of view. It proves very useful for the further development of practical solutions.
How small-scale variation in mineral wool products effect random incidence sound absorption
Authors: Bolberg Mads
Published: September 2021

Mineral wool products are produced by creating a spray of fibres, that is collected and made into slabs. This randomized spray can lead to small variations across a slab. Nevertheless, mineral wool slabs are often treated in acoustics as locally reacting perfectly homogeneous, isotropic
materials. This means that small-scale characterisations are extrapolated to large-scale without considering the impact from possible variations in a large-scale setup. The question is how the small-scale characterisations should be used for large-scale setups with this in mind. Three products
with the same thickness and density, but with significantly different specific airflow resistances were selected for random incidence sound absorption tests. The products were all specially made ceiling tiles and measurements were conducted in E200 setup according to ISO 354:2003. The tiles
were gradually exchanged in a random fashion, so measurement results were obtained using a combination of tiles with different specific airflow resistances. Results showed a surprisingly linear relation between the sound absorption and the average specific airflow resistance of tiles used
in the measurements. The results point to that variations in products must be observed, but also that small variations in specific airflow resistance in standardized products are insignificant.