The European Standardisation Organisation CEN received mandates from the European Commission to facilitate trade within the European Single Market by harmonised European standards which must be published by each of the National Standards Bodies as identical national standards.Most of these anticipated harmonised European standards are already available at least in a stage of advanced drafts.They cover the areas determination of material properties, absorption and reverberation time measurements, measurement and rating of sound insulation as well as testing of sound emission from water installations and from service equipment in buildings, on measurement of flanking transmission and also on the estimation of acoustic performance of buildings from the performance of products.The measurement of sound intensity in building acoustics and also standards on new techniques as MLS will supplement later harmonised European standards which shall form a comprehensive tool to avoid trade barriers between countries.
For the purpose of providing highly diffuse reflections, the reflection surface with periodic roughness has been often used.The degree of diffusion of this type can be evaluated by an objective measure DNSD proposed by the author.Optimum diffusers with periodic profile can be designed by using this measure, but this type of diffuse reflections might have some aspects of misgivings due to its periodicity, which may be a kind of so-called“tone coloration.”In other words, highly diffuse reflections might have a problem of some particular effect on the spectrum caused by interference between the direct and the reflected waves, which might be different from an ordinary case of the plane surface.In this paper, to clarify the physical properties and the mechanism of diffusion caused by periodic-type diffusers, SPL characteristics and impulse response of the reflected field as well as the scattering performances for three types of reflectors are discussed including the measured data from 1/8-scale model experiments.As a result of detailed discussion on the relation between the surface profile and the incident wave, the effect of periodic roughness on the reflection is revealed quantitatively.
Each of all the existing theories of the acoustic radiation pressure has, of course, peculiar excellent advantages.It is also the fact, however, that there are more or less ambiguities, leaps in logic, and unnecessary assumptions in many existing theories.The purpose of the present paper is to develop a general theory that covers both the Rayleigh and Langevin radiation pressures, and is simple and easy to understand, with merits of existing theories incorporated as far as possible.We distinguish between the Rayleigh and Langevin radiation pressures according as the force acting on an obstacle depends on a fractional change in static pressure or not.Since it is a matter of the experimental conditions whether one observes the Rayleigh radiation force or the Langevin radiation force, both radiation forces should be treated theoretically from a common physical point of view.The emphasis is placed on pointing out that the tensor properties cannot be disregarded in the Rayleigh radiation pressure as well as in the Langevin radiation pressure, by showing where the tensor term originates in.A brief review is given for a few of existing theories at the end of the chapter.
A new method, in which a sound speed profile in water is divided into layers at the points of equal sound speed above and below the SOFAR(sound fixing and ranging)axis, is proposed to calculate eigenrays for ocean acoustic tomography under range-independent sound speed profiles.The proposed method yields the following advantages over the conventional shooting method:first, it provides us with an eigenray in an analytical formula, which therefore makes the calculation time much shorter, with less quasi-eigenrays due to split beam rays at layer boundaries.Second, it allows us to easily calculate the number of eigenray cycles and to evaluate the effect caused by the discrepancy in depth between the sound source/receiver and the axis.Moreover, it clarifies how a small change in the structure of a sound speed profile above the axis relates to a structural change in a received pulse group.We can thus say that the proposed method is a promising means for identifying the received pulses.Based on a computer simulation that was performed, the three-pulse structure observed in the experiment was found to depend strongly on the relative arrangement between the source and receiver around the axis.
A single-degree-of-freedom(SDOF) system with a mass(m), a spring(k), and a damping(c) is a basic mechanical system.It is well known that a complex mechanical system is represented by a combination of infinite number of SDOF systems.The modal analysis theory is based on this principle, but only one type among various types of SDOF systems is presently employed for a modeling of complex systems.When one needs to estimate m, k, and c of a SDOF system from the measurement of the resonance frequency and the loss factor, the relationships between them must be exactly known.Those relationships are known for commonly used SDOF systems, but those for rather unfamiliar types are not known.In this technical report, various types of SDOF systems and their equivalent electrical circuits are listed, and equations that relate the resonance frequencies to the undamped resonance(natural) frequencies and the loss factors are given.It is also shown that, for some type of SDOF systems, some cares must be taken how to interpret the loss factor.
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