As our society becomes more complex, we are more surrounded by various kinds of noises such as car noise, construction noise and so on. The most common method to reduce theses noises has been a passive way to cut off them so far, however, we suggest a new way called ANC(Active Noise Control) technology.
The passive way using sound absorbing materials has been used because it is simple and inexpensive, but it also has limits and is ineffective in certain situations. On the other hand, by applying the ANC technology you can reduce the noises more effectively with simple devices.
The principle of ANC is to cancel out noise using the superposition principle of sound waves. ANC blocks the noise by generating an opposing signal (anti-noise) with the same amplitude according to the waveform of sound analyzed at the place where the noise is introduced in real time. This technology can be applied to many instruments and facilities where noise reduction is required.
Destructive interference :
The interference of two waves of equal frequency and opposite phase, resulting in their cancellation where the negative displacement of one always coincides with the positive displacement of the other.
Solution in frequency range differences
||Highly effective in low & mid frequency range below 1kHz
||Highly effective in high frequency range above 1kHz
||Both passive way and ANC technique are required
ANC Building Block
||The microphone that receives the noise to be cancelled(unwanted noise) and forwards it to the controller.
||A signal processor(usually digital) drives the speaker. In the simplest case, the DSP controller multiplies the reference microphone signal by minus one and sends it to the speaker to produce the anti-noise.
||The device that physically produces the anti-noise
||The microphone that senses the noise at the point at which noise reduction is required, and monitors how well the ANC system performs.