Air pressure on the surface of the Earth is fairly constant, so in designing a microphone for use on land, engineers don't have to worry about large variations in air pressure.
地球表面的气压相对稳定，因此设计地面用的传音器，工程师并不需烦恼气压的大幅变化。
2
If the toy has a clearly defined operating cycle, measure the time average (the equivalent continuous) sound pressure level in each microphone position during at least one whole cycle.
如果被测玩具有明显的运行周期，至少在一个完整周期内测得每个麦克风的按时平均(均等连续)声压水平。
3
Additional electronics have been added to provide film heating for calibration and to amplify the signal from the head's microphonepressure sensor.