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How Noise-Canceling Headphones Create Silence

主动降噪耳机如何制造静音

Microphones on the earcups constantly record ambient noise—like airplane engines or subway rumble—and send that signal to a digital signal processor.
The processor analyzes sound waves in real time, then generates inverse waveforms that cancel out incoming low-frequency pressure variations.
This destructive interference occurs before sound reaches your eardrum, reducing perceived noise by up to 30 decibels in the 50–500 Hz range.
Higher frequencies, such as human voices, are harder to cancel, so most headphones combine active cancellation with passive acoustic insulation from earpad materials.
Adaptive ANC adjusts continuously as you move or change environments—for example, boosting cancellation when boarding a train versus walking outdoors.
Battery power enables the electronics to run, but audio playback continues even if ANC is turned off, preserving functionality during low-charge situations.
Some models now include transparency mode, which feeds external sounds into the earpieces so users stay aware of traffic or announcements.
Engineers test ANC performance using standardized head-and-torso simulators to ensure consistent results across different ear shapes and seal qualities.

精读 · 大约 10 分钟

听 → 读 → 学表达 → 懂 → 今天会说这一句 → 跟读录音 → 自己说一句。

③ 学 · 重点表达

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。
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。
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。

④ 懂 · 选一选

这篇中文题目最接近哪一句？主动降噪耳机如何制造静音一次学校运动会的通知一份超市购物清单

课文第一句的意思更接近？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。今天学校放假了。请把窗户打开。

这一课主要在讲什么？（看英文标题） How Noise-Canceling Headphones Create Silence How to cook noodles A maths worksheet

⑤ 今天会说这一句

Microphones on the earcups constantly record ambient noise—like airplane engines or subway rumble—and send that signal to a digital signal processor.

⑥ 跟读并录音

Microphones on the earcups constantly record ambient noise—like airplane engines or subway rumble—and send that signal to a digital signal processor.

第一版：录下来、回听、再听标准音。系统打分以后再加。

⑦ 说 · 自己来一句

用今天的表达，自己说一句。

例子：Microphones on the earcups constantly record ambient noise—like airplane engines or subway rumble—and send that signal to a digital signal processor.