Effects of sound incidence angle on the effectiveness of noise reduction measures applied to acoustic windows

With more residential buildings being built close to road network systems in Hong Kong, there is an increasing need to find method to combat excessive traffic noise exposure in residentials unit. Several measures have been employed in various places, for example, vertical barrier along road with heavy traffic, acoustic balcony and acoustic windows on the façade of the residential unit. Recent addition to effective methods of reducing noise into home are micro perforated panels, and 'promute' material. These materials have various characteristic in noise reduction and can help to alleviate noise level. The orientation of the noise source with respect to the window is also an important factor to gauge whether an approach is worth using in different window setup. We tested different combination of noise reduction method on window setup that are commonly found in Hong Kong with different angle of incidence of noise source to simulate the noise from different sections of road traffic. We find that a sliding panel itself have an insertion loss of 3.5 to 7.9 dBA among different loudspeaker positions. A further 0.6-1.6 dBA is provided with plenum absorption, and the addition of MPP gives another 0.5-1.4 dBA improvement