| 摘要 |
PURPOSE:To prevent the sound pressure of a loudspeaker from being dropped, even when the used environment is varied suddenly, by providing a water-proof type vent valve for allowing a ventilation into an enclosure only when external force is applied, on a part of the enclosure. CONSTITUTION:When the titled equipment closed up helmetically and completely at the place of 20 deg.C is moved to the place of 0 deg.C and used, the internal air is cooled and contracted, then the atmospheric pressure difference is generated relatively against the open air. Therefore, pressure caused by the atmospheric pressure difference is applied to the cone 4 of a loudspeaker 3 and a sound pressure drop is generated. In this state, when the push-button 12 of a water-proof type vent valve 10 is depressed, a gap is generated between a flange 14 and a bottom part 11a, therefore, the open air passes through a gap between a shaft 12a and the flange 14 through an air filter 16 and flows in as indicated with an arrow, therefore, the sound pressure of the loudspeaker 3 is restored since it becomes and equal pressure to the open air. In such a way, the atmospheric pressure difference of the outside the inside of the equipment is obviated, a normal sound pressure can be obtained, and also, by eliminating the applied state of the external force to the vent valve, the equipment is closed up hermetically as water-proof.
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