Abstract: A vehicle internal noise reduction system and the method thereof for reducing a noise sound by producing a canceling sound from a speaker based on a tap value formed and updated in an adaptive filter, the system and the method characterized in forming the tap value of the adaptive filter by convoluting a filter coefficient having a similar band pass characteristic to a frequency characteristic of the speaker into the tap value formed by the adaptive control of the adaptive filter for the purpose of operating the noise reduction system stably without causing distortion or divergence in the system.

Abstract: In the noise reduction system to attenuate vehicle internal noise sounds by means of generating a canceling sound synthesized with an engine-originated vibration noise source signal, to prevent a remaining noise sound caused by insufficient follow-up characteristic of the adaptive filter updating at a rapid deceleration or acceleration condition of engine, while a generation of canceling sound and an updating of the adaptive filter are interrupted forcibly, the filter coefficient is reset to be a predetermined level and then therefrom a normal adaptation of the adaptive filter is restarted.

Abstract: Pulses synchronized with the period of the noise are generated and inputted to the adaptive filter. On the other hand, the tap number of the delay line of the adaptive filter is terminated at a tap number which is equal to the interval of the inputted pulse, whereby the number of times for calculation at the adaptive filter can be substantially reduced. Furthermore, in case where the tap number of the adaptive filter is changed according to the change of the period of the noise sound, the filter coefficient for cutting the high frequency domain is convoluted into the tap value of the adaptive filter, whereby noises caused by the change of the tap number can be eliminated even when the tap number of the adaptive filter is changed.

Abstract: The vehicle internal noise reduction system is characterized in being able to attenuate the internal noise sounds at a broad area of the passenger compartment by generating optimum canceling sounds from speakers disposed in the passenger compartment under any operating conditions.

Abstract: The vehicle internal noise reduction system characterized in attenuating the internal noises by generating optimum canceling sounds from speakers disposed in the passenger compartment by varying the canceling sounds with a good balance according to vehicle operating conditions as changing rapidly.

Abstract: In an automobile compartment noise reduction system, an ignition signal transforming circuit processes an ignition pulse signal to obtain a vibration noise source signal with a frequency spectrum composed of 0.5.times.n (integers) order components of the engine r.p.m. as the primary source signal. The signal is applied to an adaptive filter and an LMS calculating circuit via a speaker-microphone transmission characteristic correcting circuit. The primary source signal is synthesized by the filter into a cancel signal and then outputted through a speaker as canceling sound. The canceling sound is received by at least one error microphone at a noise receiving point as an error signal. The error signal is applied to the LMS calculating circuit. The LMS circuit updates the filter coefficients of the adaptive filter on the basis of the primary source signal and the error signal so that the error signal can be minimized. The noise reduction system has high reliability with low cost, and is easy to mount.

Abstract: A primary source is synthesized with a filter coefficient of a first adaptive filter into a canceling signal. The canceling signal is converted into a canceling sound and the canceling sound is generated from a speaker. A result of interference of the canceling sound with a noise sound is detected by a microphone as an error signal. The error signal is subjected to a sum of convolution products with the filter coefficient of the first adaptive filter in a LMS calculation circuit and the filter coefficient is updated therein. On the other hand, the error signal is subjected to a sum of convolution products with the canceling signal in another LMS calculation circuit and a filter coefficient of a second adaptive filter is updated. The updated filter coefficient of the second adaptive filter is sent to a compensation coefficient synthesizing circuit and therein the compensation coefficient is corrected by the filter coefficient.

Abstract: A noise reducing apparatus which is particularly effective to reduce periodic noise with the construction simplified very much is disclosed. The noise reducing apparatus comprises a microphone, an adaptive filter for generating a signal to reduce noise inputted to the microphone, transfer characteristic compensation means for generating a signal to compensate for a transfer characteristic when the signal generated from the adaptive filter comes the microphone, a synchronizing pulse generation circuit for generating a pulse signal synchronized with the period of the noise, a pulse interval detection circuit for detecting the interval between pulses of the pulse signal, tap number changeover means for changing over the number of taps of the adaptive filter to a number with which the delay amount of a tapped delay line of the adaptive filter is equal to the interval detected by the pulse interval detection circuit, and a loudspeaker for generating sounds in response to the signal from the adaptive filter.