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。
2
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。
3
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.