Patent Application
20110222699
The present invention relates to noise reduction at seats, more particularly, it relates to a noise reduction device and a noise reduction system to be used in an aircraft or a railroad coach.
In an aircraft or a coach where passengers are always involved with noises, the passengers in the seats sometimes cannot clearly catch information provided through audio, such as an in-flight notice, due to the noises around the seats.
The aircraft or the coach defines an interior space with continuous walls, so that the interior space forms a kind of enclosed structure. If noise sources exist inside and outside the interior space, the passengers in the interior space are to be confined within a regular noise environment. An excess noise sometimes invites physical or mental stress to the passengers, thereby degrading the convenience in the interior space. In the case of an aircraft, in particular, although flight attendants try to provide the passengers with good service in the interior space, this degradation in convenience becomes a critical problem to a service quality.
In the case of the aircraft, the following noises are chiefly involved: noises produced by the devices such as a propeller or an engine which generates thrust force for the aircraft, and noises, such as zip sound generated by the nose and the wings of the aircraft, involved with airstream produced by the movement of the aircraft in the air. The foregoing noises audible in the interior space make the passengers unpleasant and also hinder the in-flight audio notice. The noises thus need to be reduced.
Passive attenuating measures have been taken, in general, for reducing the noises in the enclosed space. This method places sound insulating material, such as a diaphragm or sound absorption material, between the enclosed structure and the noise source. The diaphragm includes, e.g. a high density diaphragm, and the sound absorption material includes, e.g. a sound absorption sheet. However, the acoustic absorption material has a high density and thus becomes a weight-gaining coefficient. An increment in the weight consumes a greater amount of fuel or reduces a flight range. As a result, the increment in the weight incurs degrading the economical and functional performances of the aircraft. On top of that, the foregoing materials have a problem of strength such as being subject to damages and a problem of design such as having a poor quality image.
Active attenuating measures have been taken for overcoming the foregoing problems caused by the passive attenuating measures, for instance, a method of generating an acoustic wave having an opposite phase to that of the noise is used generally for noise reduction. This method allows reducing the noise at the noise source or around the noise source, thereby preventing the noise from propagating to a region where noise reduction is needed. To be more specific, a noise reduction device described below has been proposed: The noise reduction device comprising:
To find an acoustic transmission function from a speaker to a noise controlling point is needed for designing an active noise reduction device. The transmission function is measured, in general, this way: A white noise having a flat frequency characteristic in a frequency control band is generated from the speaker, and a microphone placed at the control point senses this white noise. At this time, an external noise level is measured, and the white noise of which level is higher than the external noise level by a given amount, e.g. 10 dB, should be generated. This method is disclosed in Patent Literature 2.
The method disclosed in Patent Literature 2 can be used only in a case where one noise reduction device is installed, and the acoustic transmission function between the speaker and the microphone placed at the control point can be measured by the foregoing method. Patent Literature 2, however, keeps silent about a case where multiple noise reduction devices are installed. In an airplane, each one of seats is equipped with a noise reduction device, so that multiple noise reduction devices, i.e. in a quantity equal to the number of seats, need the acoustic transmission functions. In such a case, it is desired to measure fast the acoustic transmission functions of the respective seats, i.e. the noise reduction devices, free from being affected by external noises.
Patent Literature 1: Unexamined Japanese Patent Application Publication No. H01-270489
Patent Literature 2: Unexamined Japanese Patent Application Publication No. H03-259722
A noise reduction device of the present invention comprises the following structural elements:
The structure discussed above allows identifying the acoustic transmission function fast and free from influence of external noises. For instance, in a case where noise reduction devices are installed at the seats adjacent to each other, and while a first noise reduction device of the devices identifies its acoustic transmission function, a second device of the devices halts its identifying action in order not to be affected by an identification sound from the first one, and the second one starts its identifying action after the first one finishes the identifying action. As a result, both of the first and the second noise reduction devices carry out the identifying action free from being affected by the identification sound from the adjacent noise reduction device.
A noise reduction system of the present invention comprises the following structural elements:
Multiple noise reduction devices included in the noise reduction system start identifying actions sequentially following a given order of priority at intervals sufficiently shorter than an identifying time. While a subject noise reduction device undergoes the identifying action, the ambient noise level of a noise reduction device which is expected to undergo the identifying action next to the subject noise reduction device is sensed by one of the error sound sensor and the noise sensor, and in a case where the ambient noise level falls not greater than the given threshold, the next device starts the identifying action. Then an implementation of the identification is registered in the server. In a case where the ambient noise level sensed by one of the error sound sensor and the noise sensor is greater than the given threshold, the start of identifying action should be halted for a given time before the identifying action starts following the order of priority.
The foregoing structure allows a number of noise reduction devices to undergo the identifying actions simultaneously free from being affected by the identification sounds from other noise reduction devices during the identifying action, which can be thus carried out fast and accurately.
A noise reduction device in accordance with the first embodiment of the present invention is demonstrated hereinafter when the device is installed in an aircraft. The sound environment in the aircraft that needs the installation of the noise reduction devices is described with reference to
From the viewpoint of sound environment, the engine actually generates rotary sound, and the engine is a key coefficient of the noise source because it involves airstream reflection during the flight. From the viewpoint of service to passengers, engines 102a and 102b act as external noise sources NS1a, NS1b to every part of the aircraft such as seat rows 103a, 103b, and 103c installed in cabin A (e.g. first class), cabin B (business class), and cabin C (economy class) respectively. Another noise source NS1c, i.e. the aircraft moves in the air space at a high speed, so that zip sounds are produced by collision between the airstream and the nose of aircraft or the wings. This zip sound works as noise source NS1c and adversely affects in-flight services such as providing information.
Cabin 100a is situated in the sound environment where noise sources NS1a, NS1b, NS1c caused respectively by engines 102a, 102b, and the zip sound produced at the nose of the aircraft exist as external noise sources, and NS2a-NS2e caused by air-conditioners and others exist as internal noise sources. These noise sources affect, e.g. seat 105 placed in cabin A, as noises. To be more specific, seat 105 receives noises from noise source NS1a-NS1c produced by engine 102a installed to the wing outside the window (refer to
The seat in the first class in particular, i.e. in cabin A shown in
Each structural element discussed above is detailed hereinafter. Noise sensor 320 is a microphone (hereinafter referred to as a noise microphone) for sensing a noise generated by noise source 310, and also senses noise information and converts the information into an electric signal and then outputs the signal.
Noise controller 330 includes A-D converters 331, 335, adaptive digital filter 332, filter-coefficient calculator 333, and D-A converter 334. Noise controller 330 generates a controlling sound signal based on noise information supplied from noise microphone 320 and error information supplied from error sensor 350 so that a sensing error can be minimized.
Controlling sound generator 340 is a control speaker working as a controlling sound output section, and converts the controlling sound signal supplied from D-A converter 334 into a sound-wave and then outputs the sound-wave. Sound generator 340 also generates a controlling sound to be superposed on noises around ear 301b of user 301 for reducing the noises.
Error sensor 350 is a microphone (hereinafter referred to as an error microphone) that senses an error sound (residual sound) between the noise generated by noise source 310 and the controlling sound generated by speaker 340, and then converts the error sound into an electric signal before outputting this signal.
Adaptive digital filter 332 is a FIR filter formed of multistage taps. Filter coefficients of each tap can be set at any values, and the filer coefficients of adaptive digital filter 332 are adjusted so that the sensing error can be minimized. This sensing error signal supplied from error microphone 350 is input to filter-coefficient calculator 333 via A-D converter 335 in addition to the information supplied from noise microphone 320. To be more specific, a controlling sound signal having a phase opposite to that of the noise generated by noise source 310 is produced at a setting position of error microphone 350, and this controlling sound signal is supplied to controlling sound generator 340 via D-A converter 334.
Transmission function corrector 336 is a FIR filter formed of a multi-stage taps which express a transmission function of range 360. In other words, an output from adaptive digital filter 332 undergoes D-A converter 334 and control speaker 340, thereby generating the controlling sound which then travels through error microphone 350 and A-D converter 335 and finally arrives at filter coefficient calculator 333. The FIR filter expresses the transmission function of this traveling path.
A-D converter 331 A-D converts the noise signal supplied from noise microphone 320, and the resultant signal undergoes adaptive digital filter 332 and transmission function corrector 336, and finally arrives at filter coefficient calculator 333. The travel of the noise signal through corrector 336 allows an output from filter 332 to take the transmission characteristics into account. The transmission characteristics include delay, reflection on an error sound signal which has undergone the A-D conversion and is to be supplied to filter coefficient calculator 333. As a result, an accurate filter coefficient can be calculated.
Error microphone 350 working as the error sensor senses the sound having undergone the noise reduction as an error, and gives feedback to noise reduction device 300 with this error. This feedback allows minimizing noises always at user's ear even if the noise environment is changed.
As shown in
Next, a way of finding a transmission function of region 360 is described hereinafter. The work for finding the transmission function is referred to as an identifying action relative to the adaptive action shown in
During the identifying action, white-noise generator 337 working as an identification sound generator and identification controller 338 working as controlling generator 337 are used. These generator 337 and controller 338 are available in noise controller 330. Adaptive digital filter 332, filter coefficient calculator 333, D-A converter 334, A-D converter 335, controlling sound generator (control speaker) 340, and error sensor (error microphone) 350 are formed of the same components as shown in
During the identifying action, noise controller 330 outputs a noise supplied from white noise generator 337 via D-A converter 334. Differentiator 3310 finds a difference between a signal received from error microphone 350 and having undergone the A-D conversion and an output supplied from adaptive digital filter 332. This difference is referred to as an identification difference signal, which then enters filter coefficient calculator 333 together with the output supplied from white noise generator 337. Calculator 333 calculates a filter coefficient such that the identification difference signal can be minimized, and then changes the coefficient of adaptive digital filter 332 accordingly. This mechanism allows calculating coefficients of the FIR filter which expresses the transmission function of region 360.
In the environment where multiple noise reduction devices are installed, if white noises generated by the other noise reduction devices during the identifying action enter error microphone 350, the accuracy of the FIR filter of transmission function corrector 336 would be degraded. Identification controller 338 thus should determine, based on A-D converted data of the inputs to microphone 350, whether or not the white noises generated by other noise reduction devices during the identifying action around the subject noise reduction device enter the error microphone. When it is determined that no such white noises enter the error microphone, controller 338 prompts white noise generator 337 to generate a white noise, and then starts the identifying action. This mechanism allows preventing the FIR filter of corrector 336 from degrading in accuracy.
The adaptive action shown in
Next, the case where the noise reduction device in accordance with the first embodiment is installed in a cabin of an aircraft is demonstrated hereinafter with reference to
As shown in
Cabin A in the aircraft is affected by noise sources such as the engines mounted to the body, air-conditioners installed in the cabins, and others. Those noise sources generate the noises, which arrive at the outer wall of shell section 402a of seat 402. The location of head 401a of user 401 seated in seat 402 is defined as a center of the control space within shell section 402a. Assuming this center as the control center, the noise reduction device controls over this control space.
In
In this case the presence of two control speakers and two error microphones needs identifying actions shown in
In the case of selecting the identification mode, an ambient noise is measured in step S003, and the step moves on to S004 where the measured noise is determined whether or not it exceeds a given threshold. For instance, in
When the ambient noise is not greater than the threshold, a white noise is generated and then the identifying action is carried out in step S005. Steps S005, S006 and S007 are repeated until the identifying action ends.
When step S004 determines that the ambient noise exceeds the threshold, the step moves on to step S006 where a given waiting time passes before the step returns to step S004, where controller 338 determines again whether or not the ambient noise is not greater than the threshold. The waiting time in step S006 is set at the time when the noise reduction device generates the white noise. This setting allows preventing another noise reduction device from starting another identifying action although the subject device still engages in the identifying action, because this another action will adversely affect the subject noise reduction device.
In the case of selecting the adaptive mode in step S002, step S008 carries out an adaptive filtering, and step S009 monitors the change in the action mode. The adaptive filtering is repeated as long as no changes happen in the action mode. When the action mode changes to the identification mode, the step returns to step S002 and then moves on to step S003. The adaptive filtering in this context refers to this: an optimum filter coefficient is calculated by filter coefficient calculator 333, and this optimum coefficient is set at adaptive digital filter 332 for carrying out the adaptive filtering.
In the environment where multiple noise reduction devices are installed, the foregoing operation allows preventing the white noises generated by other noise reduction devices during the identifying actions from traveling into error microphone 350. Otherwise the accuracy of the FIR filter in transmission function corrector 336 is degraded. When the white noises generated during the identifying actions of other noise reduction devices are not greater than the threshold, these other noise reduction devices can undergo the identifying action at the same time as the subject device, so that the time for identifying action can be shortened.
Turn on the power supply of the noise reduction device for move the step from S010 to S011, where it is determined whether or not identification is needed. This determination can be done this way: at the initial starting the identification should be done, or it is done, e.g. once in a month, based on a periodical instruction supplied from the server.
In the case of requiring the identification, the step moves on to S012 where seat numbers that require the identification are registered. Among these registered seat numbers step S014 retrieves an order of priority, and then step S015 starts identifying (“Yes”, i.e. positive branch from decision block S014) a firstly prioritized seat. A way of prioritizing the seats is this: for instance in the case of seat arrangement shown in
After starting the identifying action in step S015, then a white noise is output in step S016, and the identifying action ends in step S017. Step S018 registers the information of ending the identification to the server. A waiting time lapses in step S019 for adjusting time until, e.g. all the noise reduction devices, which have been registered to the server as they need identification, have undergone the identifying action respectively.
In step S014, when the subject seat is not prioritized firstly (“No”, i.e. negative branch from decision block S014), the ambient noise is measured in step S020 and when the noise level is not greater than the threshold, i.e. “Yes” indicated by the positive branch from decision block S020, step S022 registers the subject seat number to the server, and the step returns to S014. In step S014 when the subject seat number is first prioritized among other seat numbers of which ambient noises are not greater than the threshold, the step moves on to step S015 for starting the identification, and then takes the same steps as discussed previously. In step S020 the ambient noise level of the subject seat exceeds the threshold, i.e. “No” indicated by a negative branch from decision block S020, the step moves on to S021, where the waiting time lapses for adjusting identification times as done in step S019. The step then returns to S011.
First, seat 1A having a higher priority than others starts identifying, and outputs the white noise (circled seat shown in
For instance, an identifying action takes five minutes, and a time difference between the seats which undergo the identifying actions at about the same time is ten seconds, then the waiting time in steps S019 and S021 can be set at minimum 5 minutes and 10 seconds after the start of identifying action of the seat firstly prioritized.
According to this second embodiment, the determination of whether or not the ambient noise exceeds the threshold is done only at the start of the identifying action, so that influence of the white noise generated from the other seats is left out of consideration after the start of the identifying action. However, since a relation between the control speaker and the error microphone is usually kept constant at each seat, the identifying action of seat 1A is affected little by the white noise generated from seat 3A, and the identifying action of seat 3A is affected little by the white noise generated from seat 1A.
However, in a case where a white noise level entering the error microphone of the subject seat during the identifying action is desirably not lower than that of a white noise level from another seat by at least 20 dB, the threshold can be set at 23 dB for having a greater tolerance.
In a case where the relation between the control speaker and the error microphone differs greatly in respective seats, the white noise generated from another seat will affect the identifying action of the subject seat. In such a case, when another seat starts identifying action, the ambient noise of the subject seat is measured again even when the subject seat engages in the identifying action. If this re-measurement finds that the ambient noise exceeds the threshold, this another seat can cancel its identifying action. In the case of the cancellation, the same waiting time as those in step S019 or S021 can be set for waiting a determination (step S011) whether or not another identifying action is necessary.
In the environment where multiple noise reduction devices are installed, the structure discussed above allows preventing the FIR filter of the transmission function corrector from degrading in accuracy. This degradation in accuracy of the FIR filter is caused by the white noise, which is generated during the identifying action of noise reduction devices other than the subject noise reduction device, entering the error microphone. The other noise reduction devices, of which white noise levels are not greater than the threshold, can undergo the identifying actions simultaneously, so that the identification time can be shortened.
In this embodiment, a white noise is used as an identification sound to be used for the identifying action; however, it is not restricted to the white noise, e.g. a pink noise can be work as well. Identification sounds restricted within a certain frequency bandwidth can be generated temporally shifted. In this case, only the sound in the same frequency bandwidth as that of the identification sound generated at the subject seat can be determined to be an ambient noise.
An instance, where the identifying action is done for targeting the transmission function of range 360, is described previously as shown in
In the exemplary embodiments discussed above, when the transmission function between the control speaker and the error microphone is identified, the ambient noise level is sensed by the error microphone and compared with the threshold; however, the ambient noise level can be sensed by the noise microphone. To the contrary when the transmission function between the control speaker and the noise microphone is identified, the ambient noise level can be sensed by the error microphone and compared with the threshold. A microphone specialized in sensing the ambient noise level can be installed.
In the embodiments discussed above, the comparison between the ambient noise level and the threshold is done at the start of the identifying action; however, the comparison can be done during the identifying action.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-057081 | Mar 2010 | JP | national |
