| 摘要 |
An active noise reduction system for an earphone 1 or ear defender, the system comprising a noise reduction sound generator 14, a microphone 5 acoustically coupled to said generator, a feedback loop connected between the microphone and generator, and including loop stabilisation means 6, 7 for filtering and inverting the phase of a microphone signal and means 12 for amplifying the signal, the sound generator 14 being mounted within an earphone or oar defender on a partition wall 16 between a rear cavity which is closed and a front cavity which is closed only when the structure is supported against a user's ear, in which the partition wall 16 is provided with an air vent hole 9 effective to equalise air pressure across the wall such that the effect of a large acoustic pressure pulse in the front cavity will be reduced in amplitude and thereby prevented from causing significant displacement of a diaphragm of sound generator 14, the diaphragm thus being able to be driven solely by the applied electrical signals. This restrains the effects of large external pressure pulses or buffets from causing damage to the diaphragm. <IMAGE> |
