Paulo Henrique Mareze

The low-frequency behavior of acoustical transducers can be simulated with the so-called electroacoustical analogies (or lumped parameters). The main idea is that visual inspection of the transducer allows the derivation of an electroacoustic circuit that can be analyzed. The technique is computationally efficient and provides significant physical insight into the transducer. Electroacoustical analogies are taught today in many courses around the world. However, it is difficult to find reading material with an algorithmic approach to derive the electroacoustic circuit from the visual inspection of the transducer. This paper presents algorithms to derive the mechanical and acoustical circuits of transducer systems and how to couple the electrical, mechanical, and acoustical circuits for electrodynamic and capacitive transducers. A number of examples of the derivation are presented in detail. These techniques were conceived from an extensive search of the classical literature in acous...

Porous materials are usually employed since they are a well-known and effective passive approach. This class of material converts the acoustical energy into heat by viscous and thermal effects. That is, this transduction is carried out by the particles' friction and movement inside the pores. Considering this scenario, it is clear that characterization of porous materials plays an important role in noise control. A common way to estimate their properties is via Kundt's Tube measurements, where the sound absorption coefficients are extracted by applying a normal incidence acoustic wave over the sample. The method is standardized by the ISO 10534-2, which recommends Class 1 instrumentation. This work presents two groups of measurements. The former case is the fruit of a low-cost measurement system, applied to a custom Kundt's Tube constructed in the Acoustical Laboratory of the Federal University of Santa Maria, in south Bra-zil. In the latter case, a commercial Kundt'...

The vibro-acoustic performance of devices with reduced physical dimensions, like hearing aid transducers, cannot be properly described using standard acoustical models. For such problems, the literature shows that visco-thermal effects must be taken into account, and analytical and numerical approaches have been previously proposed. In this paper, three models for visco-thermal acoustics are implemented and compared with experimental results: (i) the so-called low reduced frequency (LRF) model, (ii) a visco-thermal finite element with temperature variation and particle velocity as variables (three variables in 2D models), and (iii) a visco-thermal finite element with the pressure as an extra variable (four variables in 2D models). Both numerical formulations are based on a finite element discretization of the full-linearized Navier-Stokes equations (FE-FLNS) and are implemented for 2D problems. Two acoustic problems involving small dimensions and different degrees of geometric compl...

Exploring new construction materials with low environmental impact leads to innovation in buildings and also to the expansion of environmental sustainability in the construction industry. In this perspective, the thermal insulation and the sound absorption performances of Buriti (Mauritia flexuosa) foam were analyzed for potential application in buildings. This material is of plant origin, it is natural, renewable, abundant, and has a low environmental impact. In this research, characterizations were made by scanning electron microscopy (SEM), apparent density, thermogravimetry (TGA and DTG), thermal conductivity, and sound absorption. The SEM analysis revealed a predominantly porous, small, and closed-cell morphology in the vegetable foam. Due to its porosity and lightness, the material has an apparent density similar to other thermal insulating and sound-absorbing materials used commercially. The evaluation of thermogravimetric (TGA/DTG) results demonstrated thermal stability at t...

Standards have limited the allowable noise levels in different situations, requiring the study of solutions at the source, in the path or the receiver. Muffler is the major factor influencing the noise of rotary compressor. Control and analyze the acoustic characteristics of muffler is essential. Porous materials have been studied and widely applied to reduce aircraft and vehicular noise or industrial problems in general. Generally, designers use absorbing materials available on the market, however they are not always adequate to the problem when there is the presence of another gas, for example in hermetic compressors. Thus it is proposed to model the propagation in rigid porous material, characterize and develop the porous metal optimizing your acoustical absorption performance, when applied in a cavity. Direct techniques for measuring the material properties such as resistivity, porosity, tortuosity and characteristic thermal and viscous length will be studied.

Noise assessment and monitoring are essential parts of an acoustician's work since it helps to understand the environment and propose better solutions for noise control and urban noise management. Traditionally, equipment to carry out this task is standardized, and, eventually, expensive for the early career professional. This work develops a high-quality (and cost-effective) prototype for an embedded noise monitoring device based upon a digital I2S MEMS microphone and an Arduino compatible microcontroller, named Teensy. Its small size and low power consumption are also advantages designed for the project. The system captures and processes sound in real-time, computes A and C frequency-weighted equivalent sound levels, along with time-weighted instant levels with a logging interval of 125 ms. Part of the software handles the audio environment, while the biquadratic IIR filters present in the Cortex Microcontroller library are responsible for the frequency- and time-weightings - ...

Binaural rendering is a technique that seeks to generate virtual auditory environments that replicate the natural listening experience, including the three-dimensional perception of spatialized sound sources. As such, real-time knowledge of the listener's position, or more specifically, their head and ear orientations allow the transfer of movement from the real world to virtual spaces, which consequently enables a richer immersion and interaction with the virtual scene. This study presents the use of a simple laptop integrated camera (webcam) as a head tracker sensor, disregarding the necessity to mount any hardware to the listener's head. The software was built on top of a state-of-the-art face landmark detection model, from Google's MediaPipe library for Python. Manipulations to the coordinate system are performed, in order to translate the origin from the camera to the center of the subject's head and adequately extract rotation matrices and Euler angles. Low-lat...

O som é um aspecto crucial para proporcionar imersão em diversas áreas do entretenimento, afetando a experiência do usuário estética e fisicamente, principalmente no âmbito das diferentes tecnologias de reprodução disponíveis. Uma dessas tecnologias é a técnica biauricular, a qual já apresenta aplicações no entretenimento, como na música, por exemplo. No entanto, essa técnica ainda não é amplamente explorada no contexto dos jogos virtuais. Ela tem suas primeiras ocorrências mais pronunciadas na indústria apenas nos últimos 2 anos. A maior parte dos jogos virtuais atuais utilizam o áudio para fornecer feedback ao jogador, e elevar a experiência do usuário. Dessa forma, se faz relevante investigar sobre os efeitos imersivos e novas formas de gameplay que a técnica biauricular pode ocasionar ao público. O objetivo principal deste trabalho é realizar testes subjetivos por meio de um jogo virtual simplificado com as configurações de áudio biauricular e estéreo tradicional, apresentadas por fones de ouvido, a fim de obter uma avaliação subjetiva acerca da implementação da técnica biauricular quando ela influencia diretamente no gameplay e observar fenômenos gerados por sua percepção auditiva a partir de dados sobre a performance dos participantes. A configuração estéreo foi selecionada como referência para obter uma situação de comparação, pois constitui uma técnica amplamente conhecida por usuários em diversas tecnologias. O ambiente virtual para os testes foi desenvolvido com o motor de jogo Unity, e o plugin RealSpace3D foi utilizado para a implementação de HRTFs nas faixas biauriculares. Com um ambiente virtual em campo aberto e uma sala fechada, várias potenciais fontes sonoras foram posicionadas ao longo do espaço. Alternando-se entre as duas configurações de áudio, apenas uma fonte sonora é acionada por vez, e o sujeito deve localizá-la. Observou-se que, nas situações em que faixas biauriculares são apresentadas, os sujeitos localizaram as fontes com maior rapidez.

Em medições acústicas, dentre os diversos instrumentos existentes no mercado, o microfone é um dos mais utilizados. Para que se possa confiar nos resultados de uma medição, é necessário garantir que o transdutor quantifique o fenômeno físico corretamente, sendo que tais resultados são assegurados por meio de processos de calibração. Calibrar um microfone significa determinar uma relação entrada-saída para cada frequência, sua sensibilidade. Todavia, é comum que usuários em vez de calibrar os transdutores em toda faixa de frequências, realizem apenas um ajuste indireto das respostas. Nesse caso, assume-se que a resposta do microfone é aproximadamente plana (o que na prática, nem sempre acontece). Determina-se, assim, a sensibilidade e um fator de correção para uma única frequência, ajustando todo o espectro por meio desse único fator. Contudo, para algumas medições, a calibração indireta dos microfones pode não garantir a exatidão necessária, principalmente quando se utiliza alguma instrumentação de baixo custo, como microfones de eletreto, que não são projetados exclusivamente para fins de medição. Sendo assim, torna-se necessário determinar a sensibilidade de cada frequência do espectro sonoro individualmente, utilizando algum processo de calibração. Para essa finalidade, foi projetado na Universidade Federal de Santa Maria (UFSM) um pequeno acoplador de microfones, idealizado para a realização de uma calibração por comparação simultânea em campo de pressão. Normalmente, essas calibrações são processos mais complexos realizados por laboratórios acreditados. No entanto, buscou-se uma alternativa mais rápida, de relativo baixo custo e portátil, que viabiliza a realização dessas calibrações em campo. O aparato consiste em uma cavidade fechada, suficientemente pequena para simular o campo de pressão que acopla acusticamente dois microfones: um de referência e um a ser calibrado. O equipamento completo foi denominado calibrador de resposta relativa. No presente trabalho são apresentadas a concepção e a caracterização desse aparato, bem como resultados preliminares.

Porous materials are widely used for acoustical treatment and insulation of various environments. Its main feature is acoustic absorption, yielding the acoustical absorption coefficient over frequency. One of the ways to extract this parameter experimentally is with impedance tube (or Kundt's Tube) measurement via the transfer function method. However, the compression of the sample or the existence of gaps between the sample and the tube causes of uncertainty in the experiment. This research focuses upon the study of these effects. In order to analyze the influence of the boundary condition in the measurements, they were performed into two impedance tubes of slightly different internal diameters (both have the maximum frequency of analysis up to 6.4 kHz, approximately). Two different porous materials with samples of the same thickness were characterized using both tubes. In this situation, the procedure forces the influence of lateral leakage or compression of the samples against the tube to arise. Thus, this allows the analysis on the effect of the material structure in the acoustical absorption coefficient.

The system identification technique is a powerful real-time signal processing tool when dealing with the characterization of dynamic systems. This approach uses adaptive filtering techniques and the least mean square (LMS) algorithm to estimate the impulse response of a system in a finite impulse response (FIR) filter format. The main purpose of this paper is to compare the results and processing speed of two ARM-based microcontrollers as well as to give a theoretical background and an implementation procedure of the technique. ARM (Advanced RISC Machine) is an architecture of 32-bit processors usually applied in embedded systems due to its processing power, relatively low consumption, cost and small size. The impulse responses obtained by the method for several passive electronic filters were transformed to the frequency domain and compared with simulations of the circuits' frequency responses. This practice was repeated for both boards and for different parameters of the algorithm. The results have shown that the Arduino Due was unable to deal with higher sampling frequencies due to its processor limitations. On the other hand, the Teensy 3.6, a more powerful controller, yields great results even for higher frequencies.

Compressor is the main noise source of the refrigerator. With the increasing demands for quiet environment and quiet refrigerator, it’s becoming important to reduce the compressor`s noise. The main contributor of noise from the rotary compressor is the acoustically amplified pressure pulsation in the discharge manifold of the compressor. As an important method to control pressure pulsation, the discharge muffler is a crucial part influencing the compressor`s noise. The objective is to find the best rigid porous absorber to attenuate the acoustic resonances from the same compressor`s discharge chamberproperties such as resistivity, porosity, tortuosity and characteristic thermal and viscous length will be studied.

DESCRIPTION Standards have limited the allowable noise levels in different situations, requiring the study of solutions at the source, in the path or the receiver. Porous materials have been studied and widely applied to reduce aircraft and vehicular noise or industrial problems in general. Generally, designers use absorbing materials available on the market, however are not always adequate to the problem when there is the presence of another gas, for example in hermetic compressors. Thus it is proposed to model the propagation in rigid porous material, characterize and develop the porous metal optimizing your acoustical absorption performance, when applied in a cavity. Direct techniques for measuring the material properties such as resistivity, porosity, tortuosity and characteristic thermal and viscous length will be studied. Inverse methods have been developed for characterization the porous material, using genetic algorithms to extract the correct properties of these porous mate...

Modeling the surface impedance measurement of non-locally reactive porous samples is not a simple task and most of the procedures for deducing the surface impedance from in situ or free field measurements assume a locally reactive sample. The effect of this assumption is investigated in this paper. Modeling of the impedance measurement, with a PU sensor, above a non-locally reactive layer of thickness d1, is done by special numerical integration. The integration scheme is able to cope with the poles of the integrand. The modeling of the impedance measurement assumes free-field conditions and a sample infinite in extent. An iterative algorithm is used to deduce the surface impedance. The algorithm assumes free-field conditions and a sample infinite in extent and locally reactive, so that the influence of the assumption can be investigated. Measurements in the impedance tube and in a semi-anechoic room are also presented to validate the simulations and discussion. The impact the flow ...

The development of materials capable of absorbing sound in specific frequency bands has been a major goal of the research in acoustics. Thus numerical schemes that are able to capture the sound absorption mechanisms represent a very important tool for the development of new materials. In this work, the lattice Boltzmann method is used to predict the sound absorp-tion coefficient in materials with a slit-like structure. Six different simulations were conducted, taking into account different material thicknesses and porosities. Very good results were ob-served when the numerical simulations are compared with analytical results available in the literature, which suggests that the lattice Boltzmann method can be an interesting numerical tool for simulating viscous sound absorption phenomena, particularly due to its computational simplicity.

Porous materials present many important characteristics for the field of acoustics like thermal insulation, acoustic absorption, impact insulation and lightweight. There are many situations where one can find applications, such as aeronautics, automotive industries, heat and air conditioning systems, buildings, industry in general and others. Nowadays, with advances in the material fabrication process, it's possible to create complex structures according to the final objective. In this study, the greater interest is to increase sound wave absorption for industrial or residential applications. For a complete understanding of the needed characteristics to have a good absorber, it is recommended to model the structure through geometric pore reconstruction. This is a better way to later define which direction to take in order to increase the absorption curve, as well as which modifications and geometric restrictions must be performed to manufacture the best material for a given application. Simple macroscopic or empiric analytical models can be used to describe the visco-thermal dissipation inside the material. However, this approach does not present a clear link between micro and macro properties. This study proposes the reconstruction of cellular porous media using microscopic technique images. The proposed model basically is a 2D duct network made of simple uni-dimensional acoustical cylinders or pores. The theory based on acoustic transfer matrix method and mobility matrix model has been merged with analytical visco-thermal dissipation to implement the model proposed. Two cellular materials have been experimentally validated against the surface impedance and absorption for normal incidence: melamine foam and the porous aluminum. Valid agreements have been found between the experimental and numerical data. Future experiments will investigate geometry optimization methods to increase the absorption curve in frequency bands of interest.