I assume the vents around the nozzle of the phones are partially responsible for that: semi-open phones always seem to perform better than fully closed ones.
我觉得在管口的几个通气孔的作用很大，半开型耳机表现要好于全封闭的耳机。
The motor case is a steel cylinder closed tight at one end. the other end is the open throat and nozzle.
发动机壳体为一个其一端为密封的钢铸圆柱缸体，另一端则为敞口的喉道及喷管。
The needle valve can be closed through the rotation of a needle stem, and the oil cleaning device can also be driven to lift to clean out carbon deposit in the nozzle.
通过针阀杆的旋转即可以关闭针阀 又可以带动清油器升降，清除喷嘴中的积碳。
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