Acoustic Design Research Articles

Proposal of a simplified methodology for reverberation time prediction in standard medium size rooms with non-uniformly distributed sound absorption

Sabine, Eyring and Millington formulas are commonly used for reverberation time prediction, mainly, as a calculation tool in building acoustics design. These classical theories are valid only for rooms with diffuse sound fields, in which the energy density is constant throughout the enclosure, an acoustic condition that is achieved only when using surfaces with low sound absorption. Despite these limitations, Sabine’s formula is still the most widely used in the prediction of the reverberation time, when spaces such as classrooms or offices are addressed. However, for these rooms, after the construction works are completed, it is quite often verified that the implemented sound-absorbent surface area is manifestly insufficient to fulfill the reverberation time requirement. In this technical note a simplified approach for reverberation time prediction, based on the use of Sabine’s formula, is proposed, that can be useful in acoustic design of classrooms or offices, due to its simplicity. A previous correction to the sound absorption coefficient of the lining materials declared by the manufacturer is here proposed, making use of an empirical correction that was achieved fromin situexperimental results and through geometrical room acoustic modelling. The empirical correction can be employed for room conditions where diffuse sound field is not met, composed of small or medium volumes (volume below 300 m3), with regular geometry, approaching parallelepipedal shapes, where the average height is below 4.0 m.

3D-Printed Musical Instruments: Lessons Learned from Five Case Studies

The music field is lively and creative, and innovation in the final product is a leading force in the sector. However, the physical instruments used by musicians to produce their craft are highly conservative and have developed little over the last centuries. Computers, audio software, and electronic musical instruments have been integrated into musical practice, but acoustic instrument design has remained virtually frozen. Although mass production methods are frequently applied to musical instrument production nowadays, the designs have changed minimally, which makes the musical landscape unique. Additive manufacturing (AM) provides novel possibilities that can be of interest in music and musical research. In this article, we present the results of five case studies on AM use within specific musical niches. Each niche represents a unique market space and cultural background that is critical in tradition-oriented environments. Starting from the analysis of these five case studies, we extract lessons on AM application to unique environments. From these, we discuss the potential for AM-driven innovation in design and production in general and propose a holistic evaluation matrix for identifying suitable market niches.

Development of composite panels based on porous glass aerogels for acoustic applications

In this work, we present the results of research on manufacturing composite materials based on porous glass beads for acoustic treatment. A new material with fire resistance, heat resistance, impermeability, longevity, and insulation is made from foam glass beads (made from waste glass) and cement mortar. Firstly, the composite concrete panels with a high level of porosity 66%–82% and spherical pores in millimeter scale (i.e., ranging from 0.15mm to 10mm) are fabricated. Then, acoustical measurements are performed to characterize the sound absorbing coefficient and the transport properties of the selected composite panels. The measurement data are compared to the semi-phenomenological Johnson-Champoux-Allard-Lafarge model to show a good agreement in terms of predicting the sound absorption property. From the obtained results it can be stated that the open porosity and the thickness of the fabricated materials affect strongly their sound absorption performance. Within a panel thickness of 33.3mm, the aerogel-based concrete panel can provide a good sound absorption coefficient which could be more than 0.60 in the frequency range of [820 1290]Hz and reach the value of 0.84 at a low resonance frequency of ~1032Hz. The methodology, therefore, enables the identification and validation of acoustical models for specific porous glass aerogel-based materials and paves the way for an efficient exploration of the parameter space for acoustical materials design.

An archaeoacoustic study on shape: the case study of the Iffland Theatre’s history (1802–1817)

Previous studies have discussed six pre-Sabine quantifiable guidelines employed in room acoustic design: voice directivity, audience rake, “echo theory”, stage acoustics, reverberation, and length, width, and height ratios. Around the turn of the 18th century, these notions led to two shapes that were theoretically regarded optimal for rooms with acoustical demands: ellipse and semi-circle. The first of these shapes to be tested was the ellipse in the design for the Iffland Theatre (1802–1817). As the resulting acoustics were notoriously poor, contemporary architects and acousticians discussed the grounds for the failed acoustics as well as possible corrections. Multiple subsequent halls were also based on lessons learned from this acoustic failure. As part of this archaeoacoustics research, geometric acoustic numerical simulations were employed to estimate the actual and renovated room acoustic conditions. Three configurations of the hall have been reconstructed. Results show that the hall’s shape led to sound focusing and that the rounded proscenium arch likely induced echoes. Proposed solutions of the time to increase the scattering or absorption appear unlikely to have solved the observed acoustic problems.

The Concept of Acoustic Design of Propeller-Driven Fixed-Wing Aircrafts

The article proposes the concept of acoustic design of propeller-driven fixed wing aircraft, i.e., taking into account the required acoustic characteristics. The scheme of research and development work at various stage of the project necessary for the implementation of this concept is proposed. A schematic diagram of computational studies in the framework of the acoustic design process of propeller-driven fixed-wing aircraft is proposed. A schematic diagram of the choice of a propeller-driven power plant is considered, taking into account the required acoustic characteristics.

Software for Acoustic Design

Software for Acoustic Design

Material extrusion additive manufacturing of multifunctional sandwich panels with load-bearing and acoustic capabilities for aerospace applications

Reducing the noise produced by airplane engines is a significant challenge for the aerospace industry. In the present work, we investigate the design and fabrication of an acoustic sandwich panel featuring wider sound-absorbing performance compared to the currently employed technologies (e.g., perforated honeycomb cell sandwich panels). The use of material extrusion additive manufacturing (MEAM) enables us to create panels in one manufacturing step with complex geometry. The developed multifunctional (i.e., mechanical and acoustic) sandwich panel, which is based on the combination of five Helmholtz resonators, demonstrates an absorption spectrum over 517 Hz when measured with an impedance tube. The developed acoustic design, named Trapezoidal Compact (TC) sandwich, has an acoustic spectrum with more than 90% of absorption, comprised between 643 Hz and 1160 Hz. Three-point bending tests revealed that the stiffness of the sandwich panels with the TC geometry is up to ∼10% higher than those of the panels with a standard hexagonal honeycomb (HC) structure, additively manufactured with the same mass and wall thickness. The design developed in this work will contribute to the improvement of additive manufacturing process of multifunctional structures for aerospace applications.

An acoustic cloaking design based on topology optimization.

In this work, we explain how to utilize the topology optimization method for the design of acoustic cloaks based on the principle of scattering cancellation. To take account of the challenging fabrication restriction, we impose boundary control inside the optimization objective function and enforce hyperbolic tangent projection to minimize the gray transition regions of the optimized design. In addition, a filter based on the Helmholtz differential equation is used to remove any tiny structures due to the effect of discretized grids. Then, we fabricate the designed cloaks and conduct the experiments in a couple of representative set-ups to validate the proposed design approach. The experiments are conducted inside both air and water. We found that the current cloaking design performs much better in air than in water and reveal the associated reason. Overall, this work paves the way for the acoustic cloaking design, fabrication, and experiments for future practical applications.

Noise characteristics and acoustic design sensitivity of the helical gear system in wind turbine load

Noise characteristics and acoustic design sensitivity of the helical gear system in wind turbine load

Comparing the effects of scattered and specular sound reflections on speech intelligibility in rooms

Speech intelligibility in rooms is assumed to depend on the amount of reverberation, and on the distribution of sound energy in the impulse response between early and later reflections, the former being considered beneficial, the latter detrimental. This assumption is based on the analysis of a single channel, which is monaural. When the binaural capacities of the auditory system are considered, other phenomena come into play, supporting speech recognition mainly by comparing signal levels and times of arrival at the ears. Starting from these basic mechanisms, the present work shows that, for given monaural conditions, binaural cues are influenced by the type of sound reflections in a room via the correlations they produce on the signals at the ears. A fully scattering scenario, and a totally flat boundary scenario were used to investigate listeners’ performance in a speech intelligibility task in a virtual room with spatialized noise conditions. The amount of correlation at the ears of the listener of the signals coming from both the source and the masker were found to affect speech intelligibility - the stronger either correlation, the greater the speech intelligibility - and their joint effect was larger than the two effects taken separately. A specular setting for the sound reflections was associated with both better reception thresholds and a better usage of spatial cues when deciphering speech. The implications for the acoustic design of rooms with a view to facilitating speech intelligibility are discussed.

Design of a polyurethane underwater sound absorber based on the BP neural network and genetic algorithm

A coordinate transformation theory for the acoustic cloak design based on pentamode material was proposed by Norris in 2008. This theory avoids the problem of infinite density at the inner boundary of the inertial cloak, but the structural design of the pentamode material was difficult to be achieved. In order to solve this manufacturing problem, a design scheme of a low scattering cloak with only a few layers of polyurethane materials was proposed in this study. First, the material parameter distribution of the acoustic cloak was obtained based on the coordinate transformation theory. On this basis, the material parameter distribution in the two-dimensional annular acoustic cloak was derived by using linear mapping. Through simulation comparison between the uncovered acoustic cloak and covered acoustic cloak, the equivalent scattering characteristics of obstacles covered with the acoustic cloak were significantly reduced, which shows that anisotropic concealed materials have obvious advantages in acoustic control. When the thickness was given and the frequency was fixed, the sound pressure field of the cloak was simulated under the condition of uniform stratification. With the increase in the number of layers, the stealth effect was better, and the complexity of the preparation of metamaterials was increased. In order to obtain the cloak structure with a simple structure and good stealth performance, the BP neural network genetic algorithm and sound field finite element modeling were used. The minimum scattering area was taken as the optimization goal, and we tried to find the design scheme of a low scattering cloak with only a few layers of polyurethane materials. The optimization results show that when the target frequency is 2 KHz and the number of cloak layers is five, the optimized scattering area is 73% less than that of the uniformly layered structure. This shows that anisotropic stealth materials have obvious advantages in sound control. This study can guide the cell configuration design of polyurethane materials in different positions and greatly simplify the complexity of the manufacturing process of stealth materials.

Optimized Acoustic Phantom Design for Characterizing Body Sound Sensors

Many commercial and prototype devices are available for capturing body sounds that provide important information on the health of the lungs and heart; however, a standardized method to characterize and compare these devices is not agreed upon. Acoustic phantoms are commonly used because they generate repeatable sounds that couple to devices using a material layer that mimics the characteristics of skin. While multiple acoustic phantoms have been presented in literature, it is unclear how design elements, such as the driver type and coupling layer, impact the acoustical characteristics of the phantom and, therefore, the device being measured. Here, a design of experiments approach is used to compare the frequency responses of various phantom constructions. An acoustic phantom that uses a loudspeaker to generate sound and excite a gelatin layer supported by a grid is determined to have a flatter and more uniform frequency response than other possible designs with a sound exciter and plate support. When measured on an optimal acoustic phantom, three devices are shown to have more consistent measurements with added weight and differing positions compared to a non-optimal phantom. Overall, the statistical models developed here provide greater insight into acoustic phantom design for improved device characterization.

Vibroacoustic response of a high-speed train extruded profile under fluid-induced vibration

The wall pressure fluctuation caused by a turbulent boundary layer is an important source of noise and vibration in high-speed trains. Considering that railway vehicles are usually made of extruded profiles, a simple and reliable model is needed to predict the vibroacoustic characteristics of extruded profiles excited by a TBL in the early stages of design. A hybrid finite element and statistical energy analysis model is established for computing the vibroacoustic response of finite-sized panels excited by a TBL. In the hybrid model, the wall pressure fluctuation of the TBL is modelled in the wavenumber domain. The panels are modelled using FEs, and acoustic waves in the fluid space below the panels are modelled using SEA. The TBL wall pressure acting on the top surface of the panels is resolved into equivalent nodal forces with discretization of the structure using FEs, achieved by calculating the cross-spectrum matrix of the wall pressure in the spectral domain and using jinc functions with smooth boundary and symmetric properties as shape functions. The reciprocity between direct and reverberant fields couples the acoustic fields to the structure. Once the response of the hybrid model is determined, sound transmission through the panels can be calculated. By following the procedures outlined in this paper, the range of wall pressure model selection for TBL has extended and reduced computational time and provides a basis for the acoustic optimization design of extruded profiles.

Acoustic optimization design of window of high-speed train under flow-induced vibration

In this study, the sound optimization design of a high-speed train window structure under a turbulent boundary layer (TBL) pressure fluctuation is investigated. First, the Corcos model is used to characterize the cross-spectrum of the dynamic surface pressure, and analytical solutions of the window speed response, radiated sound power, and transmission loss (TL) are obtained. The effects of the cavity thickness, cavity damping, panel thicknesses, and panel damping on the TL were investigated by numerical examples. In the structural sound optimization process, the quality reduction and the sound response are essentially in conflict with each other; therefore, non-dominated sorting genetic algorithm (NSGA)-II is adopted for a dual-objective design. The numerical results show that the train speed has a significant influence on the TL of the window structure, which decreases by 4 dB when the train speed increases by 100 km/h. With the increase in the train speed, the effect of improving the TL of the window structure by increasing the thickness and damping of the window cavity gradually decreases. The TL of the window structure is more sensitive to the thickness of the window panels than that of other panels parameters; however, the thickness sensitivity decreases with the increase in the speed, whereas the improvement effect of panel damping on the TL increases with the increasing train speed. The Pareto optimal design of the window structure at 350 km/h was obtained using the NSGA-II optimization design method. The optimal design reduced the mass by 41.6 % and increased the average transmission loss (TLavg) increased by 6.2 dB compared to those of the original window structure.

Optimization of electric vehicle sound package based on LSTM with an adaptive learning rate forest and multiple-level multiple-object method

The sound absorption and sound insulation performance of an acoustic package (AP) system directly affect the noise, vibration and harshness performance of a vehicle. Numerous studies have studied the optimization of vehicle sound package, however, there are two deficiencies in the current research of sound package: (1) The noise transmission path of acoustic package is complex and hierarchical. Most of the related works focus on the data-driven part while ignoring the knowledge attributes behind the acoustic package design problem, which limits the further improvement of prediction and optimization of acoustic package performance. (2) In using intelligent neural networks-based methods such as long short-term memory (LSTM), reducing the learning rate during training gradually narrows the search interval of a solution, and adjusting the learning rate in a small range may tend to trap local optima. In this study, a knowledge- and data-driven approach is proposed for the development of acoustic package systems. A multiple-level multiple-object method is proposed as the knowledge model, and a multilayer structure of the acoustic package system that contains the system, subsystem and component layers is developed. In addition, an improved long short-term memory model based on an adaptive learning rate forest, which can increase and decrease the learning rate adaptively, is proposed as the data-driven model. The knowledge- and data-driven method is applied to optimize the sound absorption and insulation of the acoustic package system. In the experimental validation, the effectiveness and robustness of the proposed method outperformed the traditional direct mapping method and the conventional long short-term memory method.

Microstructure Design and Performance Optimization of Constant Modulus Pentamode Materials Acoustic Cloak

Underwater acoustic stealth has great scientific research value. According to acoustic coordinate transformation theory, the acoustic stealth cloak based on pentamode materials can realize underwater broadband acoustic stealth. However, due to the correlation between the density and modulus of pentamode materials and the changes in the parameters of each layer of the acoustic stealth cloak, a large amount of structural optimization work is required for the pentamode material to meet the specific parameter requirements, which significantly increases the difficulty of the pentamode acoustic stealth cloak design. To simplify the design process, inspired by the calculation of equivalent modulus by representation volume element, this article proposed a pentamode material configuration with independent variation of density and modulus and designed a 1 m radius acoustic stealth cloak with a specific structure of pentamode materials matching the coordinate transformation equation of constant modal mapping. After simulation calculation and optimization design, in the range of a/λ from 0 to 1, the average total scattering cross-section of the cavity with a radius of 0.5 m covered by the acoustic stealth cloak is 0.858; the average total scattering cross-section of the cavity is 19.718 after removing the pentamode material acoustic stealth cloak. The results of the study are expected to provide some method references for simplifying the design process of the pentamode material acoustic stealth cloak and the microstructure design of the pentamode materials.

Acoustic metamaterial design for noise reduction in vacuum cleaner

Acoustic metamaterial design for noise reduction in vacuum cleaner

A novel design scheme for acoustic cloaking of complex shape based on region partitioning and multi-origin coordinate transformation

Acoustic cloaking is an important application of acoustic metamaterials. This article proposes a novel design scheme for acoustic cloaking based on the region partitioning and multi-origin coordinate transformation. The cloaked region is partitioned into multiple narrow strips. For each strip, a local coordinate system is established with the local origin located at the strip center, and a coordinate transformation in the local coordinate system is conducted to squeeze the material along the strip length direction to form the cloaked region. To facilitate the implementation of the acoustic cloak, the multilayer effective medium is used to approximate the non-uniform anisotropic material parameters. The effectiveness of the proposed coordinate transformation method is verified by comparing the results from our method with those in the literature. Firstly, the results of a circular acoustic cloak in the literature are reproduced by using our finite element (FE) simulations for validation. Then, a comparison is made between the traditional coordinate transformation scheme and our new scheme for simulating an elliptical acoustic cloak. The results indicate that the proposed multi-origin coordinate transformation method has a better cloaking effect on the incident wave along the ellipse minor axis direction than the traditional method. This means that for the same object, an appropriate transformation scheme can be selected for different incident wave directions to achieve the optimal control effect. The validated scheme is further used to design an arch-shaped cloak composed of an upper semicircular area and a lower rectangular area, by combining the traditional single-centered coordinate transformation method for the semicircular area and the proposed multi-origin method for the rectangular area. The results show that the designed cloak can effectively control the wave propagation with significantly reduced acoustic pressure level. This work provides a flexible acoustic cloak design method applicable for arbitrary shapes and different wave incident directions, enriching the theory of acoustic cloaking based on coordinate transformation.

A perception-based study of the indoor and outdoor acoustic environments in India during the COVID-19 pandemic.

This work presents the results of a perception-based study of changes in the local soundscape at residences across India during the last 2 years of the COVID-19 pandemic and their effects on well-being, productivity during work from home (WFH), online education, anxiety, and noise sensitivity. Using emails and social media platforms, an online cross-sectional survey was conducted involving 942 participants. The responses showed that a greater percentage of participants felt that the indoor environment was noisier during the 2020 lockdown, which was attributed to increased home-entertainment usage, video-calling, and family interaction. The outdoor soundscape was much quieter during the 2020 lockdown due to drastically reduced traffic and commercial activities; however, during the 2021 lockdown, it was perceived to be comparable with pre-COVID times. While changes in indoor soundscape were shown to affect peace, happiness, and concentration while increasing annoyance, the reduction in outdoor noise positively impacted these aspects. The responses indicate that indoor soundscape changes adversely affected productivity and online education. Consequently, only 15% of participants now prefer the WFH model, while 62% have reservations about online education. In some cases, the responses demonstrate a significant influence of demography and suggest the improvement of the acoustic design of residences to support work.

Research on Broadband Matching Method for Capacitive Micromachined Ultrasonic Transducers Based on PDMS/TiO2 Particles.

The study of impedance matching between a transducer and its working medium is an important part of acoustic transducer design. The traditional quarter wavelength matching (Q-matching) scheme is not suitable for broadband capacitive micromachined ultrasonic transducers. To mitigate this issue, a 0-3 composite broadband matching layer based on polydimethylsiloxane (PDMS) substrate/TiO2 particles is designed to achieve electrical insulation and efficient acoustic energy transfer of underwater capacitive micromachined ultrasonic transducer (CMUT) devices. In this work, the coherent potential approximation model is used to analyze the properties of 0-3 composite materials. Samples are prepared for performance testing to determine the proportion of TiO2 particles that enable the 0-3 composite materials to have the same longitudinal acoustic impedance as water. The CMUT device is packaged by a spin coating and pouring process, and its performance tests are carried out. The experimental results show that the central frequency of the transducer remains at 1.74 MHz, the -6 dB fractional bandwidth increases from 97.3% to 100.3%, the 3 dB directional main beam width increases from 8.3° to 10.3°, the side lobes decrease significantly, and the device has good reception sensitivity. These values imply that the 0-3 composite material has good matching performance, and this matching scheme has the advantages of high efficiency and wide bandwidth. This broadband matching method endows CMUTs with great advantages in underwater detection systems, and it facilitates underwater ultrasonic imaging of CMUT.