| 摘要 |
PURPOSE:To prevent the vibration of a turbulence screen so as to improve noise canceling effect by providing a turbulence screen consisting of a porous elastic material and having no sound-absorbing ability in such a manner as to form an open space at the front of the detective surfaces of a noise detector attached to the inside of a duct. CONSTITUTION:Noise which propagates inside a duct 101 is detected by a detector 102. Sound having an opposite phase to the noise detected is produced in a control circuit 104. The sound of the opposite phase thus produced is released inside the duct 101 by a sound generator 104. In releasing the sound, a turbulence screen 106 of a continuously foamed porous elastic material having no sound-absorbing ability is provided at the front 105 of the detector 102 in such a manner as to form an open space 1 at the front 105. If a change occurs in a flow of air inside the duct 101, the turbulence screen 106 vibrates and the noise signal from the detector 102 undergoes modification in frequency characteristics. To deal with this problem, the vibration of the turbulence screen 106 is shut off at the space 1 and consequently the accuracy with which noise is detected and noise canceling effect are improved. |
