Volume 125, Issue 6, June 2009
Index of content:
- ARCHITECTURAL ACOUSTICS 
125(2009); http://dx.doi.org/10.1121/1.3126948View Description Hide Description
An exhaustive study has been made into the potential improvement in attenuation and focusing of phononic crystal arrays resulting from the deliberate creation of vacancies. Use is made of a stochastic search algorithm based on evolutionary algorithms called the epsilon variable multi-objective genetic algorithm which, in conjunction with the application of multiple scattering theory, enables the design of devices for effectively controlling sound waves. Several parameters are analyzed, including the symmetries used in the distribution of holes and the optimum number of holes. The validity and utility of the general rules obtained have been confirmed experimentally.
Ensemble averaged surface normal impedance of material using an in-situ technique: Preliminary study using boundary element method125(2009); http://dx.doi.org/10.1121/1.3125327View Description Hide Description
An in-situmeasurement technique of a material surface normal impedance is proposed. It includes a concept of “ensemble averaged” surface normal impedance that extends the usage of obtained values to various applications such as architectural acoustics and computational simulations, especially those based on the wave theory. The measurement technique itself is a refinement of a method using a two-microphone technique and environmental anonymous noise, or diffused ambient noise, as proposed by Takahashi et al. [Appl. Acoust.66, 845–865 (2005)]. Measured impedance can be regarded as time-space averaged normal impedance at the material surface. As a preliminary study using numerical simulations based on the boundary element method, normal incidence and random incidence measurements are compared numerically: results clarify that ensemble averaging is an effective mode of measuringsound absorptioncharacteristics of materials with practical sizes in the lower frequency range of 100–1000 Hz, as confirmed by practical measurements.
125(2009); http://dx.doi.org/10.1121/1.3125326View Description Hide Description
The notebooks of Wallace Clement Sabine were discovered in 1975, and his consulting files were discovered in 1979. Both findings were reported [J. Acoust. Soc. Am.61, 629–639 (1977); J. Acoust. Soc. Am.69, 1–7 (1981)]. By chance, his personal papers were discovered recently and highlights from them are presented here with emphasis on his European activities from 1906 to 1917.
125(2009); http://dx.doi.org/10.1121/1.3117687View Description Hide Description
This paper presents a method for calculating the directivity of the radiation of sound from a panel or opening, whose vibration is forced by the incidence of sound from the other side. The directivity of the radiation depends on the angular distribution of the incident sound energy in the room or duct in whose wall or end the panel or opening occurs. The angular distribution of the incident sound energy is predicted using a model which depends on the sound absorption coefficient of the room or duct surfaces. If the sound source is situated in the room or duct, the sound absorption coefficient model is used in conjunction with a model for the directivity of the sound source. For angles of radiation approaching 90° to the normal to the panel or opening, the effect of the diffraction by the panel or opening, or by the finite baffle in which the panel or opening is mounted, is included. A simple empirical model is developed to predict the diffraction of sound into the shadow zone when the angle of radiation is greater than 90° to the normal to the panel or opening. The method is compared with published experimental results.
A double-panel active segmented partition module using decoupled analog feedback controllers: Numerical model125(2009); http://dx.doi.org/10.1121/1.3117682View Description Hide Description
Low-frequency sound transmission has long plagued the sound isolation performance of lightweight partitions. Over the past 2 decades, researchers have investigated actively controlled structures to prevent sound transmission from a source space into a receiving space. An approach using active segmented partitions (ASPs) seeks to improve low-frequency sound isolation capabilities. An ASP is a partition which has been mechanically and acoustically segmented into a number of small individually controlled modules. This paper provides a theoretical and numerical development of a single ASP module configuration, wherein each panel of the double-panel structure is independently actuated and controlled by an analog feedback controller. A numerical model is developed to estimate frequency response functions for the purpose of controller design, to understand the effects of acoustic coupling between the panels, to predict the transmission loss of the module in both passive and active states, and to demonstrate that the proposed ASP module will produce bidirectional sound isolation.