Overhauling Sound Diffusion in Auditoria Using Deep-Subwavelength Acoustic Metamaterials

The reducedamount of space available in critical listening environments, such as orchestra pits, rehearsal rooms or even recording studios, often impairs the installation of helpful, but sizeable, acoustic treatments on their boundaries. This can be a problem as such acoustic treatments, mainly used for sound absorption and diffusion, are key for controlling the physical aspects of sound propagation in the environment. This research thus proposes to study experimentally and numerically a cutting-edge metamaterial-inspired approach designed to provide ultra-thin and adaptable alternatives to traditional acoustic treatments, with a particular focus on sound diffusion, and how these can be integrated in practical computational frameworks. These novel deep-subwavelength acoustic metamaterials, termed metadiffusers, allow for efficient sound diffusion within dimensions 1/10th to 1/20th thinner than ordinary sound diffusers. Moreover, the optimization potential of metadiffusers brings a vast panel of variable configurations depending on the situation requirements. Results presented throughout this thesis outline several of these configurations with experimental and/or numerical validations in free-field scattering scenarios as well as numerical room acoustic applications. Very good agreement is found all through between the analytical and experimental/numerical scattering and diffusion datasets, thus demonstrating the outstanding and versatile potential of metadiffusers to be applied in many critical listening environments where space is at a premium, such as orchestra pits or recording studios

Acoustics Of Classrooms

In this article we will study sound—specifically, how sound allows us to communicate in a classroom and how we can improve that communication. You will learn how sound is measured and how people called acoustics engineers help architects and designers to make sure classrooms are not too noisy—or too quiet. We even have some experiments that you can do to measure sounds at home, at school, or in a football stadium

Analysis of Broadband Directivity and FFT Response across One-Third Octave Bands for a Yaybahar vs a Cello

This paper presents an exploration of the Yaybahar, a unique stringed instrument invented by Gorkem Sen. The Yaybahar replaces the resonating body typically found in stringed instruments with a “Thunder Drum” assembly, a combination of a spring and membrane system that enhances the acoustic amplification of the instrument. The excitation of the strings is transmitted through the spring into the membrane, amplifying the output signal and augmenting the sound of the strings with a unique reverb. This results in an acoustics synthesizer that offers multiple avenues for playing, including the strings, spring, and frame drum. The aim of this study is to compare the acoustical properties of the Yaybahar with the long-established Cello to shed light on the instrument. The study focuses on comparative analysis of both the musical instruments through spectral, directivity, Fourier Frequency Transform (FFT) response and vibration transmission analysis. Despite its complex appearance, the Yaybahar is a highly expressive instrument. This paper focuses on Directionality and FFT analysis. Preliminary findings suggest that while the Yaybahar’s sound pressure levels across the frequency spectrum are lower than those of a Cello, it exhibits a similar but a stronger harmonic response. Further research is proposed to understand the behavior of springs in signal transmission/amplification and to investigate how structural integrity can sustain a note longer when the strings are plucked. Additionally, a deeper examination of the Yaybahar’s dimensions and configuration may enable higher sound pressure levels. Future work will also explore the relationship of string thickness and tuning against the steel gauge of the springs, its diameter, the membrane material, frame diameter and tuning. This will contribute to the existing knowledge about the instrument and may also provide insights into the harmonics of the spring and membrane

Acoustic conditions in orchestra pits: are metadiffusers a potential solution?

Rising concerns about public health and safety have progressively induced a change in control of noise regulations, specifically on those applicable to the work environment. These directives have been developed to protect employees from harmful side effects of their working conditions, firstly targeting high noise levels generated by heavy machinery in industry. Nowadays, noise control regulations are widely effective and applicable to nearly all working environments, including institutions dedicated to the arts, such as opera houses. To the latter, directives on noise control are of major concern as opera performances tend to generate very high sound levels, especially in the area of the orchestra pit – the sunken space between stage and audience. In such context, management faces a difficult task conforming to noise regulations as they must balance the sometimes competing demands to (i) dutifully protect their employees – musicians and others – from any harmful ‘sounds’ or ‘noise’ that might be generated, and (ii) deliver world-class operatic art for the public, where noise regulations might compromise the culture of the art form. ‘Sound’ and ‘noise’ are two terms of intense interest when dealing with control of noise regulations in the entertainment sector. Indeed, noise is generally described as ‘unwanted’ sound, judged as unpleasant, whereas music is considered most of the time as a ‘desirable’ and pleasant sound; leading to a debate on the pertinence of noise regulations within the musical arts. Such debate has recently been discussed in the High Court in London, where the court favoured an orchestral viola player who claimed to have suffered noise induced hearing loss during a rehearsal of Wagner's Valkyrie1; the major argument being that the opera house exceeded industry-wide standards on noise control, viz. daily LAE > 85 dBA. Such a case has no precedent in UK history, raising concerns for other opera houses and music spaces on how to enforce noise regulations without affecting the performances’ nature. This leads to the question of whether noise control regulations should apply to all industries, regardless of the type of sound they generate

Photovoltaic power plants: a multicriteria approach to investment decisions and a case study in western Spain

his paper proposes a compromise programming (CP) model to help investors decide whether to construct photovoltaic power plants with government financial support. For this purpose, we simulate an agreement between the government, who pursues political prices (guaranteed prices) as low as possible, and the project sponsor who wants returns (stochastic cash flows) as high as possible. The sponsor s decision depends on the positive or negative result of this simulation, the resulting simulated price being compared to the effective guaranteed price established by the country legislation for photovoltaic energy. To undertake the simulation, the CP model articulates variables such as ranges of guaranteed prices, tech- nical characteristics of the plant, expected energy to be generated over the investment life, investment cost, cash flow probabilities, and others. To determine the CP metric, risk aver- sion is assumed. 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Head-tracked auralisations for a dynamic audio experience in virtual reality sceneries

This paper aims to take advantage of the new cutting-edge virtual reality technologies – such as head-mounted displays for virtual reality and ambisonics – in order to recreate 3D immersive environments; both aural and visual. The work presented here is believed to encourage investigations into buildings yet to be, or those lost to civilisation. Through a combination of acoustic computer modelling, network protocol, game design and signal processing, this paper proposes a method for bridging acoustic simulations and interactive technologies, i.e. fostering a dynamic acoustic experience for virtual scenes via VR-oriented auralisation

Metadiffusers for quasi-perfect and broadband sound diffusion

Sound diffusion refers to the ability of a surface to evenly scatter sound energy in both time and space. However, omnidirectional radiation of sound, or perfect diffusion, can be impractical or difficult to reach under traditional means. This is due to the considerable size required by, and the lack of tunability, of typical quarter-wavelength scattering strategies necessary for producing the required complexity of the surface acoustic impedance. As such, it can be a challenge to design sound diffusing structures that can display near perfect diffusion performance within slim dimensions. In this work, we propose a method for obtaining quasi-perfect and broadband sound diffusion coefficients using deep-subwavelength acoustic diffusers, i.e., metadiffusers. The relation between the geometry of the metasurface, the bandwidth and the diffusion performance is analytically and numerically studied. For moderate bandwidths, around 1/3 of an octave, the method results in nearly perfect sound diffusion, while for a bandwidth of 2.5 octaves a normalized diffusion coefficient of 0.8 was obtained using panels 1/30th thinner than traditional phase-grating designs. The ratio between the wavelength and the size of the unit cell was identified as a limitation of the performance. This work demonstrates the versatility and effectiveness of metadiffusers to generate diffuse reflections outperforming those of classical sound diffuser