Electrical audio signal processing systems and devices – Acoustical noise or sound cancellation – Adjacent ear
Patent
1993-01-07
1994-06-07
Isen, Forester W.
Electrical audio signal processing systems and devices
Acoustical noise or sound cancellation
Adjacent ear
G10K 1116
Patent
active
053197151
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a noise sound controller that erases a noise sound by outputting from a speaker a compensation sound that has a phase opposite to and a sound pressure equal to those of the noise sound that is detected by a microphone; the noise sound controller being capable of following even a sudden change in the frequency of the noise sound.
2. Background Arts
Passive silencer devices such as mufflers have heretofore been used to suppress the noise sound generated by internal combustion engines, leaving, however, much room for improvement from the standpoint of size and silencing characteristics.
To overcome these shortcomings there has been proposed an active noise sound controller that outputs, from a speaker, a compensation sound that has a phase opposite to and a sound pressure equal to those of a noise sound generated from a noise source, in order to eliminate the noise sound.
However, putting the active noise sound controllers into practical use has been delayed because of insufficient frequency characteristics or stability thereof.
Owing to the development in recent years of signal processing technology using digital circuitry enabling a wide range of frequencies to be treated, however, many practical noise sound controllers have been proposed (see, for example Japanese Unexamined Patent Publication No. 63-311396).
The above publication discloses an active noise sound controller of the so-called two microphones and one speaker type consisting of a combination of a feedforward system and a feedback system, in which a noise sound is detected by a microphone that is installed on the upstream side of a duct to pick up the noise sound from a noise source, and is processed by a signal processing circuit and outputs, from a speaker installed on the downstream side of the duct, a signal that has a phase opposite to and a sound pressure equal to those of the noise sound, and the silenced result is detected by a microphone at a silencing point and is fed back.
On the other hand, in order to obtain a silencing effect in a space where the site of the noise source is ambiguous such as in the interior of an automobile, it is necessary to employ a device having a one-microphone one-speaker constitution using the feedback system only without installing a microphone at the noise source.
In the active noise sound controller constituted by one microphone and one speaker based on a feedback system only, however, the silencing effect decreases when the noise period of a noise source suddenly changes since the feedback system has a delay defect that is greater than the sound wave transfer characteristics from at least the speaker to the microphone.
In view of the above-mentioned problems, therefore, the object of the present invention is to provide a noise period controller that is capable of following a sudden change in the noise period.
DISCLOSURE OF THE INVENTION
FIG. 1 is a diagram illustrating the first principle and constitution of the present invention. In order to solve the above-mentioned problem, the present invention provides a noise sound controller having a sound wave-electric signal converter 2 that detects noise and converts it into an electric signal, and an electric signal-sound wave converter 3 that outputs a compensation sound wave to erase noise, wherein a noise period controller comprises a transfer characteristics simulation means 4, a differential signal calculation means 5, an adaptive filtering means 6, a period-detecting unit 7, and a period-adjusting unit 8.
The differential signal calculation means 5 calculates a differential signal between an output of the sound wave-electric signal converter 2 and an output of the adaptive filtering means 6.
The transfer characteristics simulation means 4 is inserted between the adaptive filtering means 6 and the differential signal calculation means 5, and simulates the transfer characteristics from the adaptive filtering means 6 to the differential signal calculation means 5 passing through the electri
REFERENCES:
patent: 5170433 (1982-12-01), Elliott et al.
Nagami Masaaki
Sako Kazuya
Fujitsu Ten Limited
Isen Forester W.
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