A double-leaf partition in engineering structures has been widely applied for its advantages, that is, in terms of its mechanical strength as well as its lightweight property. In noise control, the double-leaf also serves as an effective noise barrier. Unfortunately at low frequency, the sound transmission loss reduces significantly due to the coupling between the panels and the air between them. This paper studies the effect of a microperforated panel (MPP) inserted inside a double-leaf partition on the sound transmission loss performance of the system. The MPP insertion is proposed to provide a hygienic double-leaf noise insulator replacing the classical abrasive porous materials between the panels. It is found that the transmission loss improves at the troublesome mass-air-mass resonant frequency if the MPP is located closer to the solid panel. The mathematical model is derived for normal incidence of acoustic loading. 1. Introduction A double-leaf structure is a common structural design for many engineering applications. The vehicle body, such as in cars, trains and airplanes, and the walls of a building are some examples of double-leaf partition in practice. From the acoustical engineering point of view, the double leaf is proposed to be a better noise barrier compared to the single-leaf. However, there remains a problem on the double-panel which is the weak sound transmission loss (STL) performance at low frequency due to the “mass-air-mass” resonance. This causes the double leaf to lose its superiority over the single-leaf [1]. Several works have been established to solve this problem. This includes employing absorptive materials inside the gap of a double-leaf, for example, fiberglass [2] and rockwool [3] which can effectively increase the STL due to additional damping to the air layer provided by the absorbent. Mao and Pietrzko [4] proposed a technique by installing the Helmholtz resonators at the air gap. The resonator acts like single degree of freedom system of which its natural frequency depends on its geometry. In order to increase the STL at mass-air-mass resonance, the Hemholtz resonator is tuned to the same resonant frequency. Li and Cheng [5] used an active control system to control the acoustic modes in the gap by using a sound source and an actuator. The sound source reduces the transmission energy by suppressing certain acoustic modes in the air gap while the actuator reduces energy from the structural path by creating counter forces on the two panels to suppress the vibration. Similarly, Li et al. [6] used long T-shaped resonators
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