PC 121是一款挂耳式单耳通讯耳机，是廉价互联网电话和笔记本的理想选择。
The PC 121 is an over the ear monaural headset, ideal for inexpensive Internet telephony and laptop use.
声学。测听设备校准用参照区。第1部分：纯音和耳挂式耳机的参考等效阈声压级。
Acoustics - Reference zero for the calibration of audiometric equipment - Part 1 : reference equivalent threshold sound pressure levels for pure tones and supra-aural earphones.
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