| 摘要 |
PCT No. PCT/SE96/00105 Sec. 371 Date Jul. 10, 1997 Sec. 102(e) Date Jul. 10, 1997 PCT Filed Jan. 30, 1996 PCT Pub. No. WO96/23462 PCT Pub. Date Aug. 8, 1996Earmuff and method for changing the noise attenuation characteristic of an earmuff. The change is obtained by providing foam-filled sealing ring of the earmuff in the annular covering thereof with a large number of ventilation apertures 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 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", particular by using special ventilation ducts which can be dimensioned to give a selective noise transmission, dependent on the duct resonance, into the sealing ring, thereby selectively affecting the noise attenuation characteristic. |
