PURPOSE: To insulate sound wave without obstructing the flow of air as much as possible by a method wherein a multitude of sound insulating plates is provided in a ventilating port along the direction of thickness of a partitioning wall in parallel to the surface of the wall while respective sound insulating plates are provided with air passing slits.

CONSTITUTION: The ventilating ports H are provided at the upper and the lower end of the partitioning wall G and a multitude of sound insulating plates J is provided in the ventilating port H along the direction of thickness of the partitioning wall G in parallel to the surface of the wall while respective sound insulating plates J are formed with air passing slits K. According to this method, most of the sound waves are diffracted by the slits and are attenuated in spaces between the insulating plates while resistance is not caused substantially by the insulating plates with respect to the airflow moving slowly and, therefore, the flow amount of air will never be deteriorated.