| 摘要 |
An earmuff and a method for changing the noise attenuation characteristic of an earmuff. The change is obtained by providing the foam-filled sealing ring (3) of the earmuff in the annular covering (5, 6) thereof with a large number of ventilation apertures (11) which are uniformly distributed along the sealing ring, thereby affecting the air spring action of the sealing ring. The ventilation apertures communicate with the environment without communicating with the interior of the earmuff. By reducing the air spring action to a considerable extent, the low frequency attenuation is improved. The communication with the environment provides "acoustic ducts", particularly by using special ventilation ducts (12)which can be dimensioned to give a selective noise transmission, dependent on the duct resonance, into the sealing ring, thereby affecting the noise attenuation characteristic selectively.
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