A sound wave is a wave of air compression and rarefaction. If you use speakers to emit a wave with the same frequency and amplitude but with inverted phase, they weaken each other. This is the operating principle of ANC (Active Noise Control) shown in Figure 1. Active Noise Control (ANC) is a technology that can significantly reduce noise levels, especially if the sound source is well localized. ANC demonstrates even better results, if the noise spectrum has periodic components.
Promwad develops scalable embedded active noise control systems for various applications.
Areas of ANC application
- Ventilation
- Low-noise server cabinets
- Windows and soffits
- Cars and trucks
Picture 1 — ANC principle
Ventilation devices, hoods, compressors
One of the obvious applications of active noise control systems is ventilation — ventilation devices, hoods and compressors. A ventilation system with a mechanical drive is noisy, which may have an adverse effect on people who spend a lot of time on such premises. An example of such premises may be “clean” rooms where people have to work long hours. The principle of active noise control is not new: it was invented by P. Lueg as early as in 1936. However, in those times there were no technical facilities to find a modern application for an ANC system. Until recently the problem of ventilation noise was solved only by installing sound-absorbing structures, sound screens and various resonators. Now we are developing a scalable ANC ventilation system.
Listen to the demo file with ANC results:
This fragment of an audio file shows the results of modeling an ANC system. At first it is turned off and fan noise is clearly audible. Then the system is turned on and the noise decreases - periodic components disappear from the spectrum. In the above example, modeling does not include passive sound proofing, which can further improve the results.
Low-noise rackmount server cabinets
Windows and soffits
ANC in cars
Specifications
- The number of compensating speakers: 1–8
- The number of microphones / non-acoustic sensors: 2–16
- Frequency range: 20 Hz – 1000 Hz
- The level of periodic components attenuation: 25 dB
Do you want to implement active noise control technologies in your project?
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