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.
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When appropriate (e.g., for analogous circuit modeling), spatially averaged acoustic pressures and particle velocities may be assumed over relevant cross-sectional areas.
The transmission loss (TL) follows directly from this result as shown in the List of Symbols.
These statements are not necessarily true for enclosed one-dimensional source spaces (Refs. 13 and 32).
Transmission through the interstice is assumed to be completely controlled by its passive characteristics. Active control of interstice vibration is also possible (Ref. 13).
This equation corrects Eq. (13) in Ref. 7. Equations (14) and (15) of that paper also have minor errors that may be corrected by solving for and under general conditions (as outlined in the present paper), then substituting the control voltage.
The concept of minimizing volume velocity into the cavity leads to another possibility for localized error sensing. If the cavity is sufficiently small, it may be feasible to minimize acoustic pressure at a point within the cavity to produce the desired reduction of volume velocity and subsequent control of transmitting surface vibrations. However, the scheme is slightly precarious; it is possible to minimize acoustic pressure at a point in the cavity while the transmitting diaphragm is still vibrating. If small interstice vibrations or extraneous sources in the receiving space cause the transmitting diaphragm to vibrate, the acoustic pressure minimization would not necessarily eliminate sound transmission through the diaphragm and surround. In addition, if a pressure error sensor happened to be located at an uncontrolled pressure node in the cavity, the error signal might not be sufficiently observable and control complications could arise.
