criterion is amply fulfilled. This assures that a simple plot of the sampled values provides a good representation of the underlying waveform. Modern sound cards use sample rates of the order of 10 4 –10 5 samples/s, which is sufficient for all purposes. Input filter Since the received signal is to be observed rather than demodulated, the input filter should be sufficiently flat across the signal bandwidth to avoid distortion; and should have a bandwidth W i slightly larger than that of the signal. This condition can be expressed as W i ≈ 2/T p , where the factor 2 is admittedly somewhat arbitrary. Frequency-conversion filter The lowpass filter used in the frequency conversion should also be flat across the signal bandwidth, and should have a cutoff frequency W f such that 2/T p < W f 2 f c . Standard Butterworth and Chebyshev designs tend to
When dealing with nonlinear soundwaves it is quite common to maintain the speed of sound as a constant , and later we will use this hypothesis, though at high nonlinear levels the sound speed is higher than within lineal range , , and causes among other effects distortion of nonlinear soundwaves. It is also known since Sedov  that sound level decreases with distance to sound source at rates higher than within linear range. At very high nonlinear ranges it is admitted a level attenuation well above the linear range: 1/r 6 for atomic explosions, for instance, compared to 1/r 2 for linear range, due to simple spherical divergence.
At any point of a closed space, the density of energy is characterised by density emitted by the sound source and density formed by soundwaves reflecting from various planes. Let us assume that the sound source emits energy P. Then the density of direct sound at the point under consideration is equal to:
Noise barriers were modelled by Boundary-element method. Based on earlier studies, it is presumable that, in case the noise barrier is long enough (i.e. l > 300 m), two-dimensional modelling is sufficient. In case of 2D modelling, diffraction occurs only at the upper edge of the noise barrier. Element size was 0,01 m. A frequency range of 50 .. 1000 Hz was tested. I considered the barrier ideal, i.e. soundwaves might enter the shadow zone by means of diffraction – through the barrier they may not. The model considered noise barriers and the ground to be made up of rigid elements. Reductor pipe of Type 5 was made up of a special sound absorptive material.
The ocean acoustic tomography  is a technique to measure a distribution of temperatures over large regions of the ocean by accurately measuring propagation time of soundwaves that propagate through the ocean. A number of transducers consisting of a sound source and a receiver are installed around the sea area to be measured. Propagation times of soundwaves that propagate between these transducers are measured accurately. Measured changes in propagation time are converted to changes in temperature distribution through inverse problem analysis. In these analyses, the propagation path of an eigenray is usually assumed to be unchanged, and the difference in propagation time for a pulse is converted to the difference in temperature. However, the ocean contains many inhomogeneous media such as sea current, oceanic front, eddy, and microstructure. Those inhomogeneities have strong effects on the paths of sound wave propagation, making it difficult to process signals for the ocean acoustic tomography, and particularly to identify eigenrays.
The base function of humans sense of hearing is to gather information out of their environment and to use it for different purposes. The acoustical stimulus is represented by the collected soundwaves. These soundwaves, collected by the ears, include all acoustical information of interest. In other words the sound that may be measured with an artificial head for example contains all physical information as far as only the hearing system is concerned. According to Fig. 1 all sensorial information with regard to acoustics, e.g. intensity, frequency spectrum, time structure, stimulus statistics, number and arrangement of sources etc. are considered (acoustical level I and II) in that kind of recordings.
of a wave regime. An example of a synchronization wave is reported in Fig. 1(d) where we plot three successive snapshots of a wavefront propagating through the network at σ=10 and d = 0.2. The non-local coupling makes this waving phenomenon differs in many aspects from waves observed in continuous excitable media  as, for example, the fact that wavefront widths depend on the long-range coupling outreach and that propagation of coherent spatial structures like spiral waves is hindered by the shortcut links between nodes .
Fast, reliable computation techniques are needed for “real-time” design applications. A method was derived from first statistical principles, by assuming random walks of energy packets in an enclosure. The transition probabilities of the energy transfer matrix are based on the solid angle magnitudes of the enclosure walls, subtended at some particular wall centre. The room impulse response and the steady-state sound pressure level are computed. From the room impulse response, the decay curve and reverberation times are computed and some room sound quality indexes are calculated.
Sensing devices were designed and built with the following features: i) omnidirectional microphone and 30 db amplif ication; ii) 8 bit digitize of each sound sample; iii) one temperature sensor; iv) wireless Zigbee communication (ZigBee-Alliance, 2006) with the node to avoid noise in wires and connectors; and v) digital signal processor.
As in the issue of the kinds of medium so in the question of the property of the extrinsic air, the exegesis of De anima II, 8 stands in the centre of Suárez’s attention. In this chapter Aristo- tle comes with the following formulation: “The air in the ears is lodged, so as to be unmoved, in order that it may accurately per- ceive all differences of motion” (420a9-12). In this formulation, Aristotle suggests that the necessary property of the vital air in the intrinsic ear is its immobility. If it were in motion, sensorium could not perceive the oncoming sounds objectively. As the translucent (as far as colours are concerned neutral) nature of the crystalline humour in the pupil makes the pupil (objectively) receptive of the visual species, so the immobility of air makes the organ of hearing suitable for the (objective) reception of the audible species. But only a few lines below Aristotle comes with a second formulation: “… the air in the ears always moves with a special motion of its own” (420a16-7), which seems to give evidence of contrary sen- tences in one paragraph of Aristotle’s text. How does Suárez, the philosophical conciliator, harmonize them? Of which ear does Ar- istotle, as a matter of fact, speak? In an untypically less clear para- graph, Suárez at ﬁ rst appears to refer to the sensorium proper, i.e., to the intrinsic ear covered by the eardrum. Nevertheless, later on he inconspicuously moves to the external ear, which, rather than the organ, is the (adjacent) medium. Suárez makes clear that if the operation of hearing is to function well, even this “medial air” of the external ear is to be de se immobile. When Aristotle speaks about the motion, so Suárez, he does not mean that this motion is a sign of its “essence” and proper functioning. Quite on the contrary, it is a manifestation of disorder. Suárez quotes from a passage from Aristotle’s De anima following the sentence quoted above: “… sound [coming from that “special motion of its own”; D. H.] comes from an outside source, and it is not a property of the ear”. 52 Whisper in our ears is not a natural state, based on
The acoustical channel is explicitly feasible to intuitively inform the user of a product about the current status of operation and to give a feedback about the performed action. The inherently produced sound of the product often is not sufficient to give an appropriate feedback, so that additional signals have to be generated and reproduced. A patent pending method of Active Sound Design for vacuum cleaners is presented in this paper. The amount of currently aspired dust is measured, and this data is used to generate an acoustical feedback. This feedback is played back via a loudspeaker integrated into the vacuum cleaner.
RESUMO: Em 1990, o Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis (IBAMA) implantou no Brasil um programa denominado Programa Silencio (www.ibama.gov.br). Como parte desse programa foi instituído o Selo Ruído onde gradativamente eletrodomésticos, ferramentas elétricas e outros equipamentos deveriam informar ao consumidor o nível de potência sonora gerado. Para o fornecimento do Selo Ruído é necessário desenvolver o método de ensaio adequado de cada tipo de fonte, bem como credenciar laboratórios para fornece-lo. O credenciamento dos laboratórios ficou sob a responsabilidade do Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO).. Nesse trabalho são apresentados os primeiros resultados de determinação de nível de potencia sonora de furadeiras elétricas, realizados no Laboratório de Conforto Ambiental e Física Aplicada da Faculdade de Engenharia Civil da Universidade Estadual de Campinas. O procedimento de ensaio proposto baseia-se nas normas internacionais ISO 3743 Acoustics – Determination of sound power levels of noise sources using sound pressure- Engineering method for small, movable sources in reverberant fields- Part 1 Comparation method for hard-walled test rooms e Part 2 : Methods for special reverberation test rooms. Nos ensaios a sala teste foi qualificada e foram obtidos os valores de nível de potencia sonora das furadeiras. Os resultados foram analisados e pela comparação com os desvios previstos pelas normas foram considerados adequados. Para fins de Selo Ruído a metodologia proposta pela ISO 3743 mostrou-se satisfatória.
Simultaneously of those inquiries, we have done three acoustical recordings of a quarter of an hour, at different specific moments of the day and for each location of boulevards, squares, market places and school yard. The external acquisition set consists of one transducer linked to a small acquisition unit (a single channel microphone), which transfers data in real-time to a notebook computer. This instrument allows several functions such as recording the raw audio signal (like a DAT recorder), measuring the noise level time history (like a data logging integrating sound level meter) or showing the changing real-time frequency spectrum (like a frequency analyser).
The phenomenon of acousto-‐optical interaction is shown by a simple experiment. Using an acousto-‐ optic modulator recycled from a dismantled industrial laser, a laser pointer, and minimum control electronics, the action of a sound wave injected on the modulator generates the Bragg and Naman-‐ Nath diffraction regimes, depending on the geometry chosen for the interaction between the laser beam and the modulator.
The word ‘Drum Sound’ (also called room sound, emitted sound or refleted sound) is defined as perceived level of airborne sound inside a room created by falling objects, walking persons and other impact sources. The measurements of ‘Drum Sound’ are usually realized for laminate floorings, the demand for reducing this type of noise in this floorings. This paper, is presents a comparative between different types of impact sheets, in order to chek the influence of these sheets on the level of ‘Drum Sound’.
La finalidad de este proyecto es la construcción y optimización de un sound system de 3 vias que será utilizado por la asociación MCL, para diferentes tipos de eventos. El proyecto comenzó con la construcción de una caja de graves Cubo 18, y otra caja con dos unidades de medios-agudos MT-130, Una vez construidas se pasó a la fase de medida y optimización de las mismas. Se ha medido cada caja por separado, estudiando el comportamiento de cada una identificando cuales son los principales factores que afectan a su repuesta final como el uso de material absorbente, el efecto final de la bocina o la posición del cono. Una vez caracterizada cada caja se procedió a la caracterización del sistema completo mediante un procesador encargado de controlar diferentes parámetros como las frecuencias de cruce, filtros, ecualización o la asignación de retardos. Se han probado varias frecuencias y diferentes filtros hasta dar con una respuesta óptima
Perhaps the most successful endeavor in classical Magnetohydrodynamics was the proof of the existence of one and two-dimensional static equilibria, as well as the analysis of their linear stability. Among the many references we may select the classical review , and the excellent modern exposition . One of the aims of this theory is to identify perturbation frequencies which lead to exponential growth and therefore show the instability of the equilibrium. As befits a linear theory, this does not depend on the initial size of the perturbation, provided it is small enough for the linearized MHD equations to be considered valid. Nonlinear stability depends more heavily on computational algorithms, but there is an important instance where we can go a long way by analytical methods. This concerns the propagation of MHD waves into an unperturbed state, a subject forming part of the study of nonlinear hyperbolic systems [3, 4]. Both sound and MHD waves have been studied in simple special configura- tions from a long time ago [5–8], but never including the case of axisymmetric equilibria.