The essence of sound is a mechanical wave propagating along the medium, and two inverted waves can be offset under theoretical conditions. The ear noise collected by the microphone in the earphone is offset by a reversed sound wave generated by the processor and emitted by the speaker in a certain area.
After the noise reduction function is turned on, the sound waves in the main frequency band are cancelled, and the subsonic waves that cause negative feelings such as oppression, palpitation, and anxiety on the human ear are highlighted. However, the noise canceling headphones will not increase the amount of infrasound waves, and will be harmless to the human ear.
The high frequency wavelength is short and the low frequency wavelength is long. In the reverse phase cancellation process, the phase of the low frequency wave is relatively stable and the cancellation effect is better. The high-frequency wavelength is short, and because of the different ear canal structure and wearing habits of each person, it is difficult to accurately predict the high-frequency phase in a specific structure.
The speech signal spectrum band is 300Hz-3.4kHz, and the current noise canceling earphone mainly deals with the medium and low frequency signals of 50Hz 1kHz, and cannot reduce noise in the full voice frequency band.
The structural features of the noise canceling earphone: the back cavity of the earphone is not fully open, the diaphragm of the speaker is relatively thin, and the impedance is low, and the structure of the sound cavity is not conducive to the fidelity sound quality. At the same time, due to the principle of feedback noise reduction, the low frequency part of the music will be seriously lost, coupled with AD/DA conversion, the sound quality will be poor. However, the sound quality loss can be avoided by EQ adjustment.
The equalizer (EQ) is used to adjust the signals of different frequency bands to restore the frequency response curve to the trend before noise reduction. Alternatively, you can adjust the frequency response curve as needed.
At present, the main focus is on headphones and hearing aids, mainly providing products, services and solutions for active noise reduction in a small enclosed space around the ear. In contrast, cars/cabins/submarines have different requirements for noise reduction space, and the applicable services are different.
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