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

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

Recomendações técnicas para o uso agrícola do composto de lixo urbano no Estado de São Paulo.

Por que proceder a compostagem dos resíduos sólidos urbanos? Qual é a composição do lixo urbano brasileiro e paulista? Por que utilizar composto de lixo urbano na agricultura? Que efeitos pode-se esperar nas propriedades dos solos? Quais as características, maturidade e composição requeridas de compostos de lixo urbano para o seu uso na agricultura? Existe alguma legislação para o uso agrícola do composto de lixo urbano? Base científica dos índices do composto.Situação do cinturão verde de São Paulo.O risco ambiental seria apenas devido a metais pesados contidos nos resíduos sólidos? E a questão dos patógenos e outros componentes orgânicos não oferece risco à saúde das pessoas? É possível haver sanilização do solo pela aplicação do composto?Onde, quando e quanto de composto de lixo urbano deve-se aplicar nas principais culturas do Estado de São Paulo? Em síntese, que cuidados ou restrições devem ser observados para o uso agrícola do composto?bitstream/CNPTIA/9962/1/circtec3.pdfAcesso em: 28 maio 2008

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

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

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