Introduction
Noise Cancellation also recognized as active noise control involves the electro-acoustic production, normally with loudspeakers of a sound field to remove an undesired existing sound field. The favored term to describe the event is active noise control as in many cases it is arguable that cancellation is a reliable mechanism causing the unwanted noise to depreciate. Do check out some interesting information as to why do we snore?
A standard noise cancellation system consists of a receiver source sensor to inspect the disturbance to be cancelled, an electro control system to process the source signal and create the control signal, a speaker made by the control signal to produce the cancelling disturbance and as an error microphone to give the controller with information so that it can adapt itself to reduce the resulting sound field. Noise cancellation system described is recognized as an adaptive system which adapts itself to changing characteristics of the noise to be cancelled and varying environmental conditions that influence the acoustic field.
Mechanism of Noise Cancellation
To understand the physical difficulties that limit the use of active noise control, it will be useful to first address the physical mechanisms that are responsible for the noise reduction obtained by an anti-noise source. In the technique of active noise control, the cancelling signal is produced electronically and entered into the system using transducers such as speakers that change the electric signal to sound. Usually, the physical mechanism liable for the conversion of the unwanted noise is a little more complex than mere cancellation. In those cases where the cancellation is the only control mechanism, the noise level may be decreased at some locations but will be increased at others so that the total strength of the undesired noise and the cancelling sound can be conserved. This kind of control is known as local cancellation. Examples of applications using this mechanism are active headsets, where the noise is eliminated at the entrance to the ear canal but increased at other locations.
The Basic Structure of Active Noise Control Systems
The modern noise cancellation systems are made of one or more control sources used to include a secondary or controlling change into the structural-acoustic system. This change suppresses the undesired noise arising from one or more primary sources. The signals that stimulate the control actuators are created by an electronic controller, which is used as inputs and help in the measurements of the residual field and to regulate the incoming initial disturbance.
Effective noise cancellation systems are suited to use in the low-frequency limit, below approximately 500 Hz. Although higher frequency noise cancellation systems have been built, several technical problems both structural or acoustic and electronic limit their performance, so they are limited to exceptional uses. Moreover, at higher frequencies, passive systems usually become more cost-effective. A perfect noise cancellation system would normally consist of active control for low frequencies and passive control for higher frequencies.
An essential feature of many advanced active sound control systems is that they are self-tuning, means they are adaptive in nature so that they can adapt to little changes in the system being measured. Non-adaptive controllers are generally limited to the feedback type in cases where slight changes in the environmental conditions will not be caught in a significant degradation in controller performance. One example is ineffective ear protection and headsets where analogue feedback control systems have been applied successfully for some time.
Limitation and Conclusion
While noise-cancelling systems do a great job differentiating among the audio a listener wants to hear and the noise he or she wants to keep out, some say that they compromise sound quality by decreasing sounds. Despite the limitations, people would never return to standard audio systems. That is because noise-cancelling systems do more than just reducing the background noise.
