Acoustics inside a gypsum sphere with 7 m of diameter (original) (raw)
Related papers
2018
The acoustic reflection coefficients of surfaces are important parameters for geometric modeling of acoustic enclosures. They determine the frequency and incidence-angle dependent reflection characteristics of the walls and finally the overall perceptual impression of a room. The reflection coefficient of a particular material is typically determined by measuring a probe of the material in a controlled laboratory setup. This is often not possible for existing rooms, since either material samples may not be available or their exact specification. A method which allows for the in-situ estimation of acoustic reflection coefficients is therefore of practical interest. Various methods have been proposed for this purpose, e.g. [1, 2, 3]. Typically one or more sources and microphones distributed at distinct locations in the room are used. We focus in this contribution on methods that utilize (rigid) spherical microphone arrays as these are commonly used for the capture of spatial sound in ...
A Cell Model for the Acoustical Properties of Packings of Spheres
Acta Acustica united with Acustica
A new relationship between the complex density and the complex compressibility of media containing high volume fractions of spherical particles has been derived using cell models and a coupled phase approach. The combination of this relationship with an analytical expression for complex density gives a model which predicts bulk acoustic characteristics of granular materials using only three parameters: porosity, mean particle radius and an adjustable cell radius. Use of the cell radius corresponding to that of the sphere circumscribing a unit cell of a cubic lattice arrangement is proposed. By this means, the complete cell model requires only porosity and mean particle radius. Alternatively, the new similarity relationship has been combined with a semi-empirical model for the frequency dependence of dynamic density and its extension to the frequency dependence of dynamic compressibility for granular materials. The resulting model requires the knowledge of porosity, tortuosity, dc permeability (flow resistivity), mean particle radius and the cell radius. Predictions of the two models are compared with data for the acoustical properties of stacked spherical particles.
Sound Scattering and Its Reduction by a Janus Sphere Type
Advances in Acoustics and Vibration, 2014
Sound scattering by a Janus sphere type is considered. The sphere has two surface zones: a soft surface of zero acoustic impedance and a hard surface of infinite acoustic impedance. The zones are arranged such that axisymmetry of the sound field is preserved. The equivalent source method is used to compute the sound field. It is shown that, by varying the sizes of the soft and hard zones on the sphere, a significant reduction can be achieved in the scattered acoustic power and upstream directivity when the sphere is near a free surface and its soft zone faces the incoming wave and vice versa for a hard ground. In both cases the size of the sphere's hard zone is much larger than that of its soft zone. The boundary location between the two zones coincides with the location of a zero pressure line of the incoming standing sound wave, thus masking the sphere within the sound field reflected by the free surface or the hard ground. The reduction in the scattered acoustic power diminishes when the sphere is placed in free space. Variations of the scattered acoustic power and directivity with the sound frequency are also given and discussed.
Journal Audio Engineering Society Authors Version, 2011
It has been suggested by Morse and Ingard that the sound radiation of a loudspeaker in a box is comparable with that of a spherical cap on a rigid sphere. This has been established recently by the authors of this paper who have developed a computation scheme for the forward and inverse calculation of the pressure due to a harmonically excited, flexible cap on a rigid sphere with an axially symmetric velocity distribution. In this paper, the comparison is done for other quantities that are relevant for audio engineers, viz. the baffle-step response, sound power and directivity, and the acoustic center of the radiator.
The Journal of the Acoustical Society of America, 2013
Acoustic consultants are often in charge of treating spaces to fix problems or improve their room acoustics. To assess the situation and to find a solution, it is common practice to perform computer simulations. This technique is well established, cheap and effective. But it requires a CAD model of the room as well as properties of its boundaries, such as absorption and scattering coefficients. The CAD model is usually easy to obtain by asking the architect or measuring yourself, but quantifying the absorption and scattering coefficients of every single wall is a challenging task. This contribution presents a method that automatically matches absorption coefficients for every single wall by applying an inverse room acoustics model which bases on geometrical acoustics. The inversion is done numerically using a non-linear least-squares optimization process in MATLAB. The independent variables are all absorption coefficients and the goal is to minimize the error between measured and simulated impulse responses at all measured positions in the room. In addition to the acquisition of absorption and scattering coefficients, the goal after the optimization process is to perform interactive binaural auralizations that have a high perceptual congruence with the existing space.
Resonant frequency shifts induced by a large spherical object in an air-filled acoustic cavity
The Journal of the Acoustical Society of America, 2007
Acoustic resonances are modified when objects are introduced into a chamber. The magnitude of these changes depends on the object position, size, and shape, as well as on its acoustic properties. Here, an experimental study concerning the resonant frequency shifts induced by a solid spherical object in a quasi-one-dimensional air-filled acoustic cavity is reported. It is shown that Leung’s theory does not account quantitatively for the observations. A novel and simple approach is proposed, based on the wave equation in a cavity of variable cross section. The results fit more accurately the measured frequency shifts.
Acoustic Radiation from a Pair of Spheres
Acta Acustica united with Acustica
In this paper we present a semi-analytical model which enables the acoustic pressure field created by two spheres radiating close together to be predicted at any point outside the spheres. By representing the pressure field from each sphere as a finite sum of spherical harmonics and satisfying the boundary conditions at a finite number of points on the surface of each sphere, the problem reduces to the solution of a system of simultaneous linear equations whose unknown variables are the relative amplitudes of each spherical harmonic. The results from this model have been compared with those obtained using a boundary element method approach. It is shown that for values of ka < 10 both methods give results with a relative error less than 1% for separated spheres. The case for contacting spheres is discussed and results presented. Numerical examples demonstrate the accuracy and convergence rates of the two methods. A detailed analysis of the radiation problem when the spheres are in...
Sound radiation from a resilient spherical cap on a rigid sphere
The Journal of the Acoustical Society of America, 2010
It has been argued that the sound radiation of a loudspeaker is modeled realistically by assuming the loudspeaker cabinet to be a rigid sphere with a resilient spherical cap. Series expansions, valid in the whole space outside the sphere, for the pressure due to a harmonically excited cap with an axially symmetric velocity distribution are presented. The velocity profile is expanded in functions orthogonal on the cap rather than on the whole sphere. As a result only a few expansion coefficients are sufficient to accurately describe the velocity profile. An adaptation of the standard solution of the Helmholtz equation to this particular parametrization is required. This is achieved by using recent results on argument scaling of orthogonal (Zernike) polynomials. The approach is illustrated by calculating the pressure due to certain velocity profiles that vanish at the rim of the cap to a desired degree. The associated inverse problem, in which the velocity profile is estimated from pressure measurements around the sphere, is also feasible as the number of expansion coefficients to be estimated is limited. This is demonstrated with a simulation.
Influence of Standard Gypsum Board Cladding on Room Acoustic Parameters
Journal of Civil Engineering and Architecture, 2021
The purpose of this research is to investigate the effect of low-absorbent and reflective building materials (gypsum board) on the acoustic parameters of the room, depending on the type and structure of the cladding. Although gypsum board (dry cladding system) is widely used in music schools, concert halls, gyms, recording studios, their sound-absorbing properties are generally under-considered, with the main focus on their sound insulation properties. More than 10 types of boards comply with the EN520 standard; each type of board has its own sound-absorbing parameters and is used in different systems. The essence of this study is to evaluate the influence of EN520 plates on the acoustic parameters of the room: Rt; C80 and RASTI. This study does not cover all types of EN520 boards and possible combinations of their applications. This study compared four different wall-cladding systems-single-and double-layer cladding, with and without the use of stone/glass wool in order to determine acoustic properties compliance to function for sport and teaching room space.