Volume 118, Issue 3, September 2005
Index of content:
- STRUCTURAL ACOUSTICS AND VIBRATION 
A theoretical and numerical analysis of vibration-controlled modules for use in active segmented partitions118(2005); http://dx.doi.org/10.1121/1.1992767View Description Hide Description
Many applications of active sound transmission control(ASTC) require lightweight partitions, high transmission loss over a broad frequency range, simple control strategies, and consistent performance for various source and receiving space conditions. In recent years, researchers have begun to investigate active segmented partitions (ASPs) because of their potential to meet such requirements. This paper provides a theoretical and numerical analysis of four ASP module configurations that are candidates for these applications. Analogous circuit methods are used to provide normal-incidence transmission loss and reflection coefficient estimates for their passive and active states. The active control objective for each configuration is to induce global vibration control of various transmitting surfaces through direct vibration control of a principal transmitting surface. Two characteristic single-composite-leaf (SCL) configurations are unable to use the strategy effectively. However, design adjustments are investigated to improve their performances. Two double-composite-leaf (DCL) configurations use the strategy much more effectively to produce efficient global control of transmitting surface vibrations and achieve high transmission loss over a broad frequency range. This is achieved through a minimum volume velocity condition on the source side of each module. One DCL configuration enhances module isolation in full ASP arrays while satisfying other design and performance criteria.
118(2005); http://dx.doi.org/10.1121/1.1992747View Description Hide Description
Individual modules intended for active segmented partitions should be carefully analyzed before they are advanced as viable tools for active sound transmission control. In this paper we present experimental evaluations of two vibration-controlled modules: a single-composite-leaf (SCL) configuration and a double-composite-leaf (DCL) configuration. Experimental apparatuses and procedures are introduced to assess their normal-incidence transmission losses over a bandwidth from 40 to 1970 Hz. The average transmission loss of the passive SCL module is found to be 21 dB. If its transmitting diaphragm acceleration is minimized through active control, transmission loss increases somewhat at lower frequencies but decreases at higher frequencies, producing no increase in the average value. The average transmission loss of the passive DCL module is found to be 43 dB. After its transmitting diaphragm acceleration is actively minimized, the transmission loss increases substantially at all frequencies (especially at low frequencies), to produce an average value of 77 dB. Thus, while both configurations have the same underlying control objective, the DCL module yields a 56 dB average improvement over the SCL module through simple configurational changes. An alternative control scheme is investigated that minimizes acoustic pressure in the DCL module cavity, but it is found to be less effective.