Investigation of Sound Transmission through an Open Window into a Room

In recent decades, noise levels in cities and the associated annoyance and health consequences have become regular topics of discussion. As a result, the assessment of environmental noise transmitting into buildings has received much attention. Current models of sound transmission through open windows have either neglected their thickness or the presence of a room behind on one side. The objectives of the present work were to (1) develop an accurate analytical model of sound transmission through an open window of finite thickness into a room, (2) verify the analytical model using a finite element model and experimental measurements, and (3) to express the various regions of the model in terms of impedance matrices. The motivation behind the third objective is that active noise control design based on the impedance-mobility approach has shown much promise, and the mathematical combination of impedance matrices representing two distinct regions linked by a finite aperture has not been considered. To better understand the mechanics by which sound transmits through the window, the present investigation developed an analytical model of a baffled rectangular aperture of finite thickness backed by a rigid walled cavity. The effect of aperture thickness on the insertion loss and sound pressure levels inside the cavity was studied with the analytical model, which was validated by a finite element model of the system. Increasing window thickness decreases the amount of sound transmitted at frequencies below the (1,1) mode of the cavity. Using the impedance-mobility approach, the model can be extended to consider many noise control treatments to windows including active noise control. Figure 2.1 – Present model of sound transmission into a cavity through an aperture of Figure 3.1 – FEM model with the cavity on the right for a) large and b) small source Figure 3.2 – Experimental setup. Two coordinate systems were used with origins indicated by stars, one for the source room and one for the cavity. Dots labeled BK# and LD# indicate microphone and sound level meter locations, Figure 4.6 – Comparison of present model and aperture only for large, deep aperture .. 40 Figure 4.7 – Comparison of present model and aperture only for large, medium aperture