| 摘要 |
An active noise reduction system is disclosed which includes an earphone to be acoustically coupled to a listener's ear when exposed to noise. The earphone comprises a cup-like housing with an aperture; a transmitting transducer which converts electrical signals into acoustical signals to be radiated to the listener's ear and which is arranged at the aperture of the cup-like housing, thereby defining an earphone cavity located behind the transmitting transducer; a receiving transducer which converts acoustical signals into electrical signals and which is arranged behind, alongside or in front of the transmitting transducer; a sound-guiding tube-like duct having two ends; one end is acoustically coupled to the receiving transducer and the other is located behind, alongside or in front of the transmitting transducer; a first acoustical path which extends from the transmitting transducer to the ear and which has a first transfer characteristic; a second acoustical path which extends from the transmitting transducer through the tube-like member to the receiving transducer and which has a second transfer characteristic; and a control unit which is electrically connected to the receiving transducer and the transmitting transducer and which compensates for the ambient noise by generating a noise reducing electrical signal supplied to the transmitting transducer. The noise reducing electrical signal is derived from the receiving-transducer signal, filtered with a third transfer characteristic, and in which the second and third transfer characteristics together model the first transfer characteristic. |
