The displacement ventilation is widely applied in industrial buildings, civil buildings and public buildings, especially in the auditorium of large theaters, meeting rooms, and cinemas. Because the diffusers are installed near to peoples under the chairs, the air flow from them must be controlled both comfortably and quietly. When the airflow noise level of the diffuser is equal to or lower than that of background in the test lab, it is hard to accurately measure the noise emitted by it. The airflow noises of kinds of chair diffusers were measured by the precision methods in reverberation room and it was found that there was a well linear relationship between the airflow noise and the logarithm of the air volume. A noise level curve can be achieved by linear fitting on the reliable noise of the higher speed airflow. And the airflow noise for very low speed can be calculated by this curve.
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