A model for manufacturing doors and windows which are capable of natural ventilating, reducing traffic noise
and so on for the developing tropical countries is presented. These windows and doors combine two basic components
which are ventilation unit and lighting unit. Due to the fact that the ventilation unit must have a large volume to attenuate
low frequency noise, many resonance of higher-order mode wave will be generated inside the unit. In this work, a method
to predict the insertion-loss of rectangular ventilation unit with input and output openings at various positions is proposed
by solving the wave equation, considering the resonance frequencies of higher-order mode. The results of the analysis
have been confirmed by experiments.