WO2013118636A1 - 消音装置 - Google Patents
消音装置 Download PDFInfo
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- WO2013118636A1 WO2013118636A1 PCT/JP2013/052223 JP2013052223W WO2013118636A1 WO 2013118636 A1 WO2013118636 A1 WO 2013118636A1 JP 2013052223 W JP2013052223 W JP 2013052223W WO 2013118636 A1 WO2013118636 A1 WO 2013118636A1
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- noise
- signal
- microphone
- adaptive filter
- ultrasonic
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- 230000003044 adaptive effect Effects 0.000 claims abstract description 44
- 210000003454 tympanic membrane Anatomy 0.000 claims abstract description 34
- 238000004422 calculation algorithm Methods 0.000 claims description 23
- 230000003584 silencer Effects 0.000 claims description 11
- 238000012937 correction Methods 0.000 claims description 5
- 238000012546 transfer Methods 0.000 claims description 4
- 238000013459 approach Methods 0.000 claims description 2
- 238000004364 calculation method Methods 0.000 claims description 2
- 230000007613 environmental effect Effects 0.000 description 13
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- 238000001514 detection method Methods 0.000 description 7
- 238000012545 processing Methods 0.000 description 7
- 230000006870 function Effects 0.000 description 6
- 210000005069 ears Anatomy 0.000 description 4
- 230000030279 gene silencing Effects 0.000 description 3
- 230000001902 propagating effect Effects 0.000 description 3
- 230000005236 sound signal Effects 0.000 description 3
- 238000013528 artificial neural network Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000002068 genetic effect Effects 0.000 description 2
- 230000001743 silencing effect Effects 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 208000009205 Tinnitus Diseases 0.000 description 1
- 239000011358 absorbing material Substances 0.000 description 1
- 230000002457 bidirectional effect Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
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- 230000003595 spectral effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000011410 subtraction method Methods 0.000 description 1
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- 238000002604 ultrasonography Methods 0.000 description 1
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- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1785—Methods, e.g. algorithms; Devices
- G10K11/17861—Methods, e.g. algorithms; Devices using additional means for damping sound, e.g. using sound absorbing panels
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1785—Methods, e.g. algorithms; Devices
- G10K11/17853—Methods, e.g. algorithms; Devices of the filter
- G10K11/17854—Methods, e.g. algorithms; Devices of the filter the filter being an adaptive filter
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1785—Methods, e.g. algorithms; Devices
- G10K11/17857—Geometric disposition, e.g. placement of microphones
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1787—General system configurations
- G10K11/17879—General system configurations using both a reference signal and an error signal
- G10K11/17881—General system configurations using both a reference signal and an error signal the reference signal being an acoustic signal, e.g. recorded with a microphone
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/02—Casings; Cabinets ; Supports therefor; Mountings therein
- H04R1/028—Casings; Cabinets ; Supports therefor; Mountings therein associated with devices performing functions other than acoustics, e.g. electric candles
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
- H04R1/1083—Reduction of ambient noise
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- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
- H04R3/002—Damping circuit arrangements for transducers, e.g. motional feedback circuits
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
- H04R3/005—Circuits for transducers, loudspeakers or microphones for combining the signals of two or more microphones
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/10—Applications
- G10K2210/128—Vehicles
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/30—Means
- G10K2210/321—Physical
- G10K2210/3221—Headrests, seats or the like, for personal ANC systems
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/30—Means
- G10K2210/321—Physical
- G10K2210/3226—Sensor details, e.g. for producing a reference or error signal
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- H—ELECTRICITY
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- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2217/00—Details of magnetostrictive, piezoelectric, or electrostrictive transducers covered by H04R15/00 or H04R17/00 but not provided for in any of their subgroups
- H04R2217/03—Parametric transducers where sound is generated or captured by the acoustic demodulation of amplitude modulated ultrasonic waves
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2410/00—Microphones
- H04R2410/05—Noise reduction with a separate noise microphone
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2460/00—Details of hearing devices, i.e. of ear- or headphones covered by H04R1/10 or H04R5/033 but not provided for in any of their subgroups, or of hearing aids covered by H04R25/00 but not provided for in any of its subgroups
- H04R2460/01—Hearing devices using active noise cancellation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
- H04R2499/10—General applications
- H04R2499/13—Acoustic transducers and sound field adaptation in vehicles
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R5/00—Stereophonic arrangements
- H04R5/02—Spatial or constructional arrangements of loudspeakers
- H04R5/023—Spatial or constructional arrangements of loudspeakers in a chair, pillow
Definitions
- the present invention relates to a silencer that cancels noise reaching the ear from various directions.
- FIG. 1 is a diagram for explaining a silencing technique for silencing noise in a pipe.
- Bidirectional noise is generated in the pipe 101.
- the noise generated in the pipe 101 is transmitted to the pipe 102 and is transmitted in one direction from the left side to the right side in FIG.
- a noise detection microphone 103 and an error signal detection microphone 104 are provided in the pipe 102.
- an LMS (Least Mean Square) adaptive filter 105 for inputting output signals from the microphone 103 and the microphone 104 is provided, an amplifier 106 for amplifying the output of the LMS adaptive filter 105, and a silencer for inputting the output of the amplifier 106.
- a speaker 107 is arranged.
- the LMS adaptive filter 105 will be described later, an active silencer using the LMS adaptive filter is often used due to the recent development of digital signal processing technology.
- the LMS adaptive filter 105 is a filter that works so that the error signal output by the microphone 104 detecting and outputting the noise-eliminated sound is as close to ‘0’ as possible.
- the output signal of the LMS adaptive filter 105 is inverted and amplified by the amplifier 106 and supplied to the mute speaker 107. Since the sound wave output from the muffling speaker 107 is a sound wave having a phase opposite to that detected by the microphone 103, the noise propagating in the pipe 102 is canceled out. Therefore, the noise detected by the microphone 104 is infinitely close to “0”. Here, the distance between the microphone 103 and the speaker 107 needs to be 30 cm or more apart in order to ensure time for signal processing by the LMS adaptive filter 105. Further, only noise transmitted in one direction can be silenced by this method.
- the example shown in FIG. 2 is an example in which noise generated from the noise source 200 propagates from three directions including reflection from the floor and ceiling.
- noise generated from the noise source 200 propagates from three directions including reflection from the floor and ceiling.
- a noise detection microphone 201 and an error signal detection microphone 202 are provided, and these are supplied to the LMS adaptive filter 203.
- the output of the LMS adaptive filter 203 is input to the amplifier 204, inverted and amplified, and supplied to the speaker 205.
- the processing in the LMS adaptive filter 203 is the same as that of the LMS adaptive filter 105 in FIG.
- the distance from the noise source 200 to the microphone 202 is different between the path a and the paths b and c, the phase of the noise reaching along the path a and the noise reaching along the paths b and c The phases are different. Therefore, the sound wave output from the speaker 205 when the LMS adaptive filter that receives the signal from the microphone 201 functions has an opposite phase to the noise detected by the microphone 201.
- a canceling headphone a noise detection microphone placed near the ear has been used to generate noise in the opposite phase to the noise applied to the earphone, and this opposite phase signal is added to the signal from the earphone speaker.
- a device for canceling noise has been proposed (see, for example, Patent Document 1).
- a microphone that converts ambient noise into an electrical signal is provided in a headphone unit that covers the user's ears, and the noise detected by the microphone is reversed in phase and the sound that enters the user's ears. Add to (Signal + Noise).
- the noise from which the noise has been removed is transmitted to the user's ear, and a headphone in which ambient noise has been canceled (noise canceled) is realized.
- FIG. 3 shows an example of canceling headphones.
- a headphone attached to the ear is provided with a noise detection microphone 301 and a speaker (earphone) 302, and a noise signal detected by the noise detection microphone 301 is converted into a reverse phase by an inverting amplifier 303 and then supplied to the speaker 302. Has been.
- Patent Document 2 A noise removal device has also been proposed (see, for example, Patent Document 2).
- the technique described in Patent Document 2 generates a cancellation signal from an environmental sound signal recorded at a viewing position, and modulates the carrier frequency by a synthesized acoustic signal obtained by synthesizing the cancellation signal and an audio frequency signal (for example, an audio signal). Then, it is supplied to the ultrasonic speaker.
- FIG. 4 shows that noise is eliminated by detecting noise reaching the ear and supplying it to the speaker in reverse phase without providing a shielding plate for preventing howling. That is, noise from the noise source 400 is detected by the microphone 401, and this signal is supplied to the speaker 403 at the ear via the LMS adaptive filter 402.
- Patent Document 2 The technique described in Patent Document 2 is to pick up the noise at the position where the sound is heard with a microphone and superimpose the noise cancellation signal and the ultrasonic signal to remove the noise.
- FFT First Fourier Transform
- the mechanism for canceling noise is complicated, such as selecting the frequency band of noise to be deleted using the so-called SS method (Spectral Subtraction Method) that subtracts the frequency spectrum of environmental noise stored in advance in the buffer. There is a problem.
- An object of the present invention is to provide a silencer that cancels out noise that comes into the ear from a random direction like a rear seat of a vehicle without contact with a headphone without using a headphone, and with a simpler configuration. There is.
- the silencer of the present invention inputs a super-directional microphone that pinpoints noise in the spot area at the ear and a noise signal output from the super-directional microphone, and reverses the noise signal.
- An adaptive filter that outputs a phase signal, and an ultrasonic speaker that generates an ultrasonic wave toward the ear by modulating a carrier signal in an ultrasonic band output from the transmitter by the signal of the adaptive filter.
- the ultrasonic wave generated by the ultrasonic speaker reaches the eardrum and is demodulated into audible sound by the eardrum, the demodulated audible sound has an opposite phase to the noise detected by the superdirective microphone.
- the ultrasonic speaker used in the silencer of the present invention includes a modulator, and in this modulator, the carrier signal in the ultrasonic band is modulated by a signal having a phase opposite to that of the noise signal from the directional microphone. The Then, the signal modulated by the modulator is applied to the actuator, and the modulated ultrasonic wave generated from the actuator propagates to the human eardrum. Although the modulated ultrasonic wave reaches the eardrum, the ultrasonic wave is not heard and only the demodulated sound is heard, so that the noise reaching the ear is eliminated.
- the silencer of the present invention When the silencer of the present invention is installed in a headrest such as a rear seat of a car, for example, it has the effect of reducing as much as possible the noise audible to the ears of a person sitting on the seat.
- FIG. 5A is a diagram showing that the ultrasonic wave emitted from the ultrasonic speaker 500 reaches the eardrum of the ear and is converted into an audible sound.
- the ultrasonic wave is FM-modulated and transmitted to the eardrum, and the eardrum vibrates with noise and simultaneously with the demodulated sound wave. Since these two vibrations are in opposite phases, they are canceled out. As a result, the noise is canceled out and silenced.
- FIG. 5B is a diagram schematically showing the directivity of the ultrasonic speaker 500.
- the directivity of the ultrasonic speaker 500 extends in the direction of the central axis with a spread of about 15 ° to 30 °, even if it is slightly away from the ear, Ultrasound reaches the eardrum.
- FIG. 6 is a simulation diagram illustrating the distance in the central axis direction of the ultrasonic speaker 500 and the sound pressure level at a position in a direction perpendicular to the central axis.
- the ultrasonic speaker 500 has a strong directivity and propagates to a distance of about 90 cm with respect to the central axis direction. In other words, if the ultrasonic speaker 500 is arranged at a distance of about 20 to 30 cm from the ear, it is clear that the ultrasonic wave reaches the ear drum.
- the ultrasonic speaker 500 when the ultrasonic speaker 500 is used, even if it is disposed at a position slightly away from the human ear, the ultrasonic wave generated there can reach the human eardrum, and the ultrasonic wave can be heard by the eardrum.
- the ultrasonic speaker 500 emits an ultrasonic wave of 50 kHz
- the eardrum converts it to an audible sound of 1 kHz which is the difference.
- the eardrum has a function of modulating ultrasonic waves as a nonlinear element.
- the ultrasonic speaker 500 has a diameter of about 1 cm and is already commercially available from each company. By arranging this ultrasonic speaker in the headrest of the rear seat of the vehicle, it is possible to apply ultrasonic waves only to the ears of the person to be muffled (the person sitting on the rear seat). Note that the driver may not be able to hear sound from the surroundings, so the ultrasonic speaker 500 is not disposed on the headrest of the driver's seat.
- FIG. 5C is a diagram for explaining the operation principle when the eardrum is vibrated in a phase opposite to the noise using the ultrasonic speaker 500.
- the ultrasonic speaker 500 modulates a carrier wave (frequency: 50 kHz) from a carrier wave signal transmitter 501 corresponding to the ultrasonic frequency by a signal (band about 1 kHz) 502 having a phase opposite to that of a noise signal detected by a super-directional microphone described later. Including a modulator 503. Then, the modulation signal modulated by the modulator 503 is supplied to an actuator (speaker) 505 via an amplifier 504.
- the modulated ultrasonic wave generated from the actuator 505 is transmitted as a virtual sound source 506 to human hearing (the eardrum) 507, where it is converted into an audible sound having a bandwidth of about 1 kHz. Since this audible sound is superimposed with a signal having a phase opposite to that of the noise, the sound wave from which the noise has been removed reaches the human eardrum.
- FIG. 7 is a diagram schematically showing the super-directional microphone 600 used in the embodiment of the present invention and the directivity characteristics thereof.
- a super-directional microphone 600 By using such a super-directional microphone 600, even at a position away from the ear, It shows that noise around the ear can be detected.
- the sound at the place where the microphone is placed can be detected, but the sound at a target place (for example, around the ear) that is a little away is detected. It becomes difficult.
- various types of super-directional microphones 600 are available on the market, and can be selected as appropriate.
- the frequency that can be picked up by this super directional microphone 600 is an audible sound of 20 kHz or less, and an ultrasonic wave exceeding 20 kHz cannot be detected. Therefore, even if the ultrasonic speaker 500 is disposed at a position close to the super-directional microphone 60, the ultrasonic wave transmitted by the ultrasonic speaker 500 is not detected. That is, even if the ultrasonic speaker 500 and the super-directional microphone 600 are arranged close to the headrest of the rear seat, the super-directional microphone 600 is not affected by the sound emitted from the ultrasonic speaker 500, and therefore no howling occurs. Actually, since it is necessary to gain processing time in the LMS adaptive filter 700 (see FIG. 8) described later, the ultrasonic speaker 500 and the super-directional microphone 600 are placed at a distance of about 20 cm in the headrest. Arranged.
- FIG. 8 shows an embodiment of the present invention.
- an ultrasonic speaker 500 including a super-directional microphone 600, a modulator 503, and an actuator 504 is disposed at a position away from the eardrum 601 by a predetermined distance (about 20 cm).
- a nonlinear microphone 602 is provided in the vicinity of the eardrum 601. As will be described later, this nonlinear microphone 602 is used only once when the coefficient adjustment of the LMS adaptive filter 700 is performed. When the coefficient adjustment is actually finished, this coefficient update is performed. This nonlinear microphone 602 is not used because it is not necessary.
- the LMS adaptive filter 700 it is possible to generate an erasure signal with a simple configuration. That is, there is no need for a buffer, and it is not necessary to perform processing with a large amount of calculation such as FFT (First Fourier Transform).
- FFT First Fourier Transform
- the ear noise is converted into an electric signal by superdirective microphone 600, and the converted signal is input to coefficient variable filter 701 of LMS adaptive filter 700.
- the noise at the ear is also converted into an electrical signal by the non-linear microphone 602.
- the coefficient correction algorithm 702 performs arithmetic processing, and the coefficient of the coefficient variable filter is corrected based on the result. .
- the coefficient correction algorithm 702 corrects the coefficient of the coefficient variable filter 701 by working so that the signal of the nonlinear microphone 602 approaches zero.
- the frequency characteristics of the non-linear microphone 602 are the same as those of the superdirective microphone 600.
- the nonlinear microphone 602 has lower linearity and larger distortion than the super-directional microphone 600.
- the reason for using this nonlinear microphone 602 is that the nonlinear microphone 602 is very similar to the nonlinear characteristics of the eardrum. That is, similarly to the eardrum 601, when this nonlinear microphone 602 receives an ultrasonic wave, it is demodulated by the nonlinear characteristic, and the ultrasonic wave is converted into an audible band sound.
- the reason why the non-linear microphone 602 is arranged in the vicinity of the eardrum is to replace the actual eardrum 601 as described above.
- This non-linear microphone 602 can simulate a sound in which an ultrasonic wave is actually converted into an audible range by a human ear, and the mute state is always optimized by feeding back a silencing error with the non-linear microphone 602. Can keep.
- the environmental noise detected by the superdirectional microphone 600 is sent to the modulator 503 of the ultrasonic speaker 500 as an output of the LMS adaptive filter 700, and is modulated by the modulator 503 at an ultrasonic frequency of about 50 kHz.
- the sound wave generated from the actuator 504 of the ultrasonic speaker 500 becomes an erasing sound having a phase opposite to that of the environmental noise.
- the coefficients of the LMS adaptive filter 700 are updated so as to learn the transfer function from the superdirectional microphone 600 to the eardrum 601. That is, the coefficient of the LMS adaptive filter 700 is set so as to be an inverse function of the transfer function of the acoustic propagation system between the superdirectional microphone 600 and the eardrum 601.
- the LMS adaptive filter 700 is used to generate a signal having a phase opposite to that of the noise detected by the directional microphone 600, but the coefficient has already been set. After that, since the coefficient is not updated, the LMS adaptive filter 700 operates as a general FIR (Finite Impulse Repose) filter.
- FIR Finite Impulse Repose
- an algorithm as an LMS adaptive filter is used.
- the LMS algorithm is a modified complex LMS algorithm (Complex / Least / Mean / Square / Algorithm) or NLMS algorithm / (Normalized / Least / Mean). Square Algorithm) is also included.
- the projection algorithm (Projection Algorithm), SHARF algorithm (Simple Hyperstable Adaptive Recursive Filter Algorithm), RLS algorithm (Recursive Least Square Algorithm), FLMS algorithm (Fast Least Mean Square Algorithm)
- Other adaptive filters such as filters (Adaptive Filters using Discrete Cosine Transform), SAN filters (Single Frequency Adaptive Nonch Filters), neural networks (Neural Networks), and genetic algorithms (Genetic Algorithms) can perform similar processing. it can.
- FIG. 9 is a diagram for explaining that an ultrasonic wave and an audible sound have different frequency bands, and that interference does not occur even when an ultrasonic wave is emitted toward a noise source.
- the ultrasonic waves generated from the ultrasonic speaker 500 of FIG. since environmental noise and ultrasonic waves have different frequency bands, the ultrasonic waves generated from the ultrasonic speaker 500 of FIG. Then, it is demodulated into a sound having a phase opposite to that of the environmental noise.
- environmental noise in-phase signal
- FIG. 8 environmental noise (in-phase signal) also reaches the eardrum 601. Therefore, in the eardrum 601, a sound having a phase opposite to that of the environmental noise is simultaneously added, and as a result, the noise is canceled and muted. .
- the positional relationship between the environmental noise entering the super-directional microphone 600 and the ultrasonic speaker 500 that generates sound having a phase opposite to that of the environmental noise is determined by the ultrasonic speaker 500 being a super-directional microphone. Since it is far from (behind) the eardrum 601 from 600, the sound of the ultrasonic speaker 500 is somewhat delayed by this distance. For this reason, it is difficult to mute over all frequencies of the environmental noise, and a particularly high sound muffling effect is reduced.
- the operation principle and the embodiment of the present invention have been described with respect to the non-contact silencer in which the ultrasonic speaker and the super directional microphone are arranged on the headrest of the rear seat of the car.
- the present invention is not necessarily applied, and can be applied to a vehicle other than an automobile, for example, a train, an airplane, or a ship seat. Further, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and application examples are included without departing from the scope described in the claims.
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- Acoustics & Sound (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Otolaryngology (AREA)
- Circuit For Audible Band Transducer (AREA)
- Soundproofing, Sound Blocking, And Sound Damping (AREA)
- Fittings On The Vehicle Exterior For Carrying Loads, And Devices For Holding Or Mounting Articles (AREA)
Abstract
Description
このような状況は自動車内の環境でも同じであり、したがって、車内に入ってくる騒音を完全に除去することは、極めて困難であった。
まず、本発明の実施形態に用いられる超音波スピーカと超指向性マイクについて説明する。
図5(A)は、超音波スピーカ500から発せられた超音波が耳の鼓膜に到達し、可聴音に変換されることを示す図である。マイクで検出した信号と逆相の信号を超音波スピーカ500に加えることにより、超音波がFM変調されて鼓膜に伝わり、鼓膜が、騒音で振動すると同時に、復調された音波で振動する。この2つの振動が逆相であるので相殺され、結果として騒音が相殺されて消音されることになる。
図7は、本発明の実施形態に用いられる超指向性マイク600とその指向特性を模式的に示した図であり、このような超指向性マイク600を用いることで耳元の離れた位置でも、耳元周辺の騒音が検出できることを示している。超指向性マイク600の代わりに、通常のマイクを用いた場合には、そのマイクを置いた場所の音の検出はできるが、少し離れた目的の場所(例えば、耳周辺)の音の検出は難しくなる。また図2で説明したように多方向から入ってくる騒音を検出することも困難である。この超指向性マイク600も、超音波スピーカ500と同様に、様々な種類のものが市場に出回っているので、その中から適宜選択することが可能である。
図8は、本発明の実施形態例を示すものであるが、最初にLMS適応フィルタ700の動作について説明する。本発明の実施形態例では、鼓膜601から所定距離(20cm程度)離れた位置に超指向性マイク600及び変調器503とアクチュエータ504を含む超音波スピーカ500が配置される。また、鼓膜601の近辺には非線形マイク602が設けられている。この非線形マイク602は、後述するように、LMS適応フィルタ700の係数調整を行うときに1回だけ用いられるものであり、係数調整が終わった後で実際に動作させる場合には、この係数更新は必要ないのでこの非線形マイク602は使用しない。
ここでLMS適応フィルタ700を用いることにより、簡単な構成で消去信号を生成することができる。すなわち、バッファを必要とすることもなく、FFT(First Fourier Transform)のような演算量の多い処理を行う必要がない。
耳元の騒音は非線形マイク602によっても電気信号に変換され、変換された信号がLMS適応フィルタ600に入力されると係数修正アルゴリズム702により演算処理されてその結果により係数可変フィルタの係数が修正される。この係数修正アルゴリズム702は、非線形マイク602の信号がゼロに近づくよう働いて係数可変フィルタ701の係数を修正する。
図9に示すように、環境騒音と超音波とは周波数帯域が異なるので、図8の超音波スピーカ500から発生される、環境騒音の逆相信号で変調された超音波は、鼓膜601に到達すると環境騒音とは逆相の音に復調される。一方、図8に示すように環境騒音(同相信号)も鼓膜601に到達するので、鼓膜601では、環境雑音と逆相の音が同時に加わることになり、結果的に打ち消されて消音される。
Claims (5)
- 耳元のスポットエリアの騒音をピンポイントで検出する超指向性マイクと、
該超指向性マイクが出力する騒音信号を入力して該騒音信号と逆相の信号を出力する適応フィルタと、
該適応フィルタの信号により発信器が出力する超音波帯域の搬送波信号を変調して耳元に向けて超音波を発生させる超音波スピーカと、
を備える消音装置。 - 前記超音波スピーカは、
前記搬送波信号を前記適応フィルタの信号によって変調する変調器と、
該変調器の信号を入力して超音波を発生するアクチュエータと、
を備える請求項1に記載の消音装置。 - 前記超指向性マイクは、鼓膜周辺の騒音をピンポイントで検出することができるピンポイントマイクである、請求項1に記載の消音装置。
- 前記適応フィルタは係数可変フィルタと係数修正アルゴリズムを備えたLMS適応フィルタであり、
鼓膜の近傍に設けた非線形マイクの信号を入力して前記係数修正アルゴリズムの計算結果に応じて前記係数可変フィルタの係数を修正するとともに、前記非線形マイクの信号がゼロに近づくよう働くことを特徴とする請求項1に記載の消音装置。 - 前記LMS適応フィルタの伝達関数は、前記超指向性マイクと前記鼓膜の間の音響伝搬系の伝達関数の逆関数となるように調整される、請求項4に記載の消音装置。
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