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How Noise-Canceling Headphones Create Silence
主动降噪耳机如何制造静音
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Microphones on the earcups constantly record ambient noise—like airplane engines or subway rumble—and send that signal to a digital signal processor.耳罩上的麦克风持续采集环境噪音（如飞机引擎声或地铁轰鸣），并将信号传送给数字信号处理器。
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The processor analyzes sound waves in real time, then generates inverse waveforms that cancel out incoming low-frequency pressure variations.处理器实时分析声波，然后生成反向波形，抵消入耳的低频压力变化。
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This destructive interference occurs before sound reaches your eardrum, reducing perceived noise by up to 30 decibels in the 50–500 Hz range.这种相消干涉发生在声音抵达耳膜之前，可在50–500 Hz频段内最多降低30分贝的感知噪音。
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Higher frequencies, such as human voices, are harder to cancel, so most headphones combine active cancellation with passive acoustic insulation from earpad materials.人声等高频声音较难消除，因此多数耳机结合主动降噪与耳垫材料提供的被动声学隔音。
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Adaptive ANC adjusts continuously as you move or change environments—for example, boosting cancellation when boarding a train versus walking outdoors.自适应主动降噪会随用户移动或环境变化持续调整——例如，上火车时增强降噪，而户外行走时减弱。
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Battery power enables the electronics to run, but audio playback continues even if ANC is turned off, preserving functionality during low-charge situations.电池为电子元件供电，但即使关闭主动降噪，音频播放仍可继续，确保低电量时基本功能不受影响。
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Some models now include transparency mode, which feeds external sounds into the earpieces so users stay aware of traffic or announcements.部分型号新增通透模式，将外部声音传入耳道，帮助用户留意交通声或广播通知。
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Engineers test ANC performance using standardized head-and-torso simulators to ensure consistent results across different ear shapes and seal qualities.工程师使用标准化的头 torso 模拟器测试主动降噪性能，以确保不同耳型和佩戴密封性下的结果一致性。