Active Noise Control of Vehicle Engine Noise Based on Sound Generation and Radiation Characteristics

Abstract

This study examined an active noise control (ANC) method using the characteristics of the sound radiation. This study provided an effective active noise control system for noise that travels externally through an exhaust gas muffler. An analysis of diesel engine noise and its frequency characteristics was performed. The noise radiation formation was calculated for certain low frequency engine noise and was simulated. A double or quadruple sound source was constructed to reduce the engine noise that is radiated as a single sound source formation. An active noise control algorithm was developed to use when the characteristics of the noise are exactly determined. A microphone was located on the area where the sound pressure is minimized when creating a sound field of a multi-sound source to create an active noise control system that uses multi sounds. In the situation where it is hard to install a sensor or an actuator inside, such as an environment with a high temperature and humidity, a method in which the radiation characteristics change by using a synthesized signal algorithm is the most effective. From such methods, an active noise control system that decreases the noise from a diesel engine and exhaust gas muffler was constructed. An optimized active noise control system was provided to control the engine noise coming from a closed space. The characteristics of the sound from a construction machine cabin were measured and analyzed. The inner sound field was tested to understand the sound field created by an inner space. A white noise was used to measure the response function, and the inherent vibration was theoretically calculated for the closed space. A reference microphone that could reflect the characteristics of a changing noise was used and two error microphones were constructed to reduce the noise level at a driver’s seat. The distance between the control speaker and the error microphone was shortened to apply a headrest structure that could quickly and accurately control the noise. A two-single-channel algorithm that could be used when the cross path’s effect could be ignored was provided. The filter that reflects the psychoacoustic reaction of the driver was applied to the active noise control algorithm. The reduction effect was confirmed by locating the microphones at different locations at the construction machines, and the noise was reduced by considering the inner sound field. The reference signal and combination method were used to reduce the noise at the cabin model and the actual machine. A 3D sound method was used to expand the area of noise reduction. The control sound source was located in the same path as the sound noise source and the listener in an active noise control system to reduce the noise effectively. This study used many speakers to use a wave field synthesis method that locates a virtual control sound at a noise-propagating path. WFS is a method that creates a plane wave and, thus, could be used on active control of a low frequency noise. WFS method uses the Huygens principle as its base and the Kirchhoff–Helmholtz equation was used to calculate the magnitude and phase of each speaker using a speaker array, location of the listener, and the placement of the speaker. A computer simulation was performed to prove the creation of a plane wave at a listener’s level. It was confirmed that the sound pressure of both ears was reduced. The improvement of the performance was observed by comparing the active noise control system that uses WFS and the original noise control system.