Volume 118, Issue 6, December 2005
Index of content:
- ARCHITECTURAL ACOUSTICS 
118(2005); http://dx.doi.org/10.1121/1.2114587View Description Hide Description
The feasibility of applying active noise control in large rooms, in which global control is very difficult, is investigated. Local control can only ensure sound attenuation near error-sensor positions. Considering that workers usually work only in certain regions of a workroom, a new “locally global” control strategy is proposed. The objective is to reduce the acoustic potential energy in the target region. Compared to local control, “locally global” control ensures overall noise reduction over the target region. Compared to global control, it allows the number of control channels to be significantly reduced. The placements of the controlloudspeakers and error microphones must be optimized to ensure that, while the sum of the squared sound pressures at the error sensors is minimized, the potential energy in the target region is reduced. Room sound fields are modeled using the image-source method and point sources. Genetic algorithms are used to optimize the locations of the controlloudspeakers and error microphones. Both numerical and experimental results are presented. The sensitivities of control performance to variations in the excitation frequency, the control-source positions, and the error-sensor locations are investigated.
Acoustic eigenvalues of rectangular rooms with arbitrary wall impedances using the interval Newton∕generalized bisection method118(2005); http://dx.doi.org/10.1121/1.2114607View Description Hide Description
Modal analysis of a rectangular room requires evaluation of the eigenvalues of the Helmholtz operator while taking into account the boundary conditions imposed on the walls of the room. When the walls have finite impedances, the acoustic eigenvalue equation becomes complicated and a numerical method that can find all roots within a given interval is required to solve it. In this study, the interval Newton∕generalized bisection (IN∕GB) method is adopted for solving this problem. For an efficient implementation of this method, bounds are derived for the acoustic eigenvalues and their asymptotic behavior explored. The accuracy of the IN∕GB method is verified for a canonical problem by comparing the modal solution with the corresponding finite elementsolution. Furthermore, reverberation times estimated using the IN∕GB method are compared to those calculated using the finite difference method. Through these examples, it is demonstrated that the IN∕GB method provides a useful and efficient approach for estimating the acoustic responses of rectangular rooms with finite wall impedances.
118(2005); http://dx.doi.org/10.1121/1.2118267View Description Hide Description
The sound wave in the air between the fibers of glass wool exerts an oscillatory viscous drag on the fibers and excites a mechanical wave in the fiber skeleton. Accurate calculations of sound attenuation in glass wool must take the mechanical wave in the fiber skeleton into account, and this requires knowledge of the dynamic elastic constants of the fiber skeleton. The mechanical properties of glass wool are highly anisotropic. Previously only one of the elastic constants has been measured dynamically, but here all the elastic constants are reported. The measurement method is well known. But a new mechanical design, which reduces mechanical resonance, is described. The measurements were carried out in atmospheric air at normal pressure, and this causes an oscillatory airflow in the sample. To obtain the elastic constants, the influence of the airflow was subtracted from the data by a new formula. The elastic constants were measured in the frequency range for glass wool of mass density . The elastic constant depended on the frequency; at it was , and at it was . The constant did not depend on frequency. The shear constant was constant. The two constants were zero.
The development of a Component Mode Synthesis (CMS) model for three-dimensional fluid–structure interaction118(2005); http://dx.doi.org/10.1121/1.2114567View Description Hide Description
Our main aim in this paper is to develop analytically the three-dimensional Component Mode Synthesis method and to use it on fluid–structure interaction problems, such as sound transmission between coupled volumes. This will be shown for simple volume geometries, but, in principle, the same procedure can be applied when the component modes are obtained from numerical techniques, such as the Finite Element Model(FEM) or Boundary Element Method (BEM). The modal behavior of acoustic volumes and a partition is implemented in two steps. The first extension here is based on a one-dimensional model where the transverse acoustic modes of the volumes are incorporated into the formulation. The second extension, which is more general, considers not only the transverse acoustic modes of the volumes, but also structural modes of the partition. A comparison is made with predictions based on a modal model using the normal modes of rigid walled enclosures separated by a simply supported partition. For the latter modal model,particle velocity continuity was not incorporated in the formulation.