1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling noise generated in a confined space, and a method of and an apparatus for controlling noise generated in a confined space, being capable of reducing a radiating sound pressure (including vector components) generated from a main noise source to that of an optimal state.
2. Description of the Prior Art
Generally, noise generated from mechanical devices which are operated inside or outside of confined spaces such as cabs, ship's cabins, vehicle interiors or office rooms is the factor for causing workers in the confined spaces to be uncomfortable. Such noise also results in a degradation in work efficiency. To this end, a variety of noise reducing techniques have been proposed.
Among known noise reducing techniques, One relatively efficient method is a system using an additional sound source (for example, a speaker) adapted to interfere with a noise source in phase, thereby being capable of obtaining a noise offset effect. In this connection, much researches in positive noise control techniques have been actively made. This technique is efficiently applicable even to a frequency band noise where it is difficult to expect a noise reducing effect by using only a sound absorbing material or sound shielding material (for example, a low frequency band of about 500 Hz). Among systems using this technique, the generally known one Is the system wherein a sensor is attached to a desired area in a confined space where noise is problematic (for example, the driver's seat in a cab). The sensor serves to drive the additional sound source In order to minimize noise at the desired area.
However, the positive noise reduction technique has many problems as follows.
First, although the noise reduction effect is obtained at the area, where the sensor Is installed, by virtue of a noise offset effect generated at the area, the generation of noise may rather be increased at other areas because no noise offset effect is generated at those areas.
Second, where it is desired to obtain the noise reduction effect in a large space, it is necessary to install a plurality of sensors respectively at a plurality of areas in the space, thereby performing a multi-channel signal processing. In this case, a complex control should be performed so as to accurately execute the multi-channel signal processing. However, such a complex control requires a high-speed, large discrete signal processing unit. As a result, the overall system is expensive. Furthermore, this system has a degraded performance, resulting In a degraded utility.
Third, it is actually difficult to determine an optimal installation position of the sensor. For example, although the sensor is attached to the head support of the driver's seat in the interior of the cab, it can not provide an optimum noise reduction effect when the driver moves from his seat to another position during the operation of the mechanical device.