نوشته شده توسط مهدی نوروزی فر دسته: الکتروآکوستیک
نمایش از 17 ارديبهشت 1392 بازدید: 60127
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 Abstract

If sound is annoying or loud enough to damage hearing, it is called noise. Noise has many  effects  on  people . In  addition  , hearing loss, and lowers performance in mental and physical tasks. Conventionally, noise  reduction  has  been  implemented  with  vibration  isolators , acoustical absorbing materials , enclosures , barriers , and  vibration damping  materials. Generally , these approaches  to  the noise control are a relatively inexpensive way to reduce noise. They are  called  passive  noise control  methods because they do not need power  to operate .  At low frequencies , the  noise  reduction  levels  achieved  are  often  inadequate  and  control  of  low frequency  noise with passive methods only is  often  impractical as well as costly. For example, mufflers  must  be  large and  absorbing  walls heavy to reduce noise levels effectively. Fortunately, active noise control can complement passive noise control . The idea behind active noise  cancellation  is to generate opposite  phase  sound  that  destructively interferes  with  the existing sound field. Active methods are more costeffective and capable of adapting noise levels at low frequencies, but at higher frequencies of, say, over 500 Hz, complex sound fields and the larger computational load needed in a control system due to higher sampling rates limits system performance greatly. Comprehensive noise control solutions often combine both of these approaches. Active noise control is a combination of acoustics, signal processing, and mechanics. Although the principles behind active noise control are rather well understood, one has to have a detailed understanding of the limitations and possibilities of those areas to be able to produce a practical application for active noise control. The concept of ANC was patented for the first time in the 1930s, but not until the 1990s did practical implementations became available. In the 1990s, control algorithms and the computing power of digital signal processors were developed to a sufficient level to make practical control systems possible. Nowadays there are not many industrial applications using active noise control, but practical systems can be found, for example, in active headsets, airconditioning ducts, and propeller aircraft.

Keywords : Active Noise Control, simulation model, modelling, control system.

 

 

 

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