Classifications

• • 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
  • G10K11/17883—General system configurations using both a reference signal and an error signal the reference signal being derived from a machine operating condition, e.g. engine RPM or vehicle speed
• • 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
  • G10K11/1781—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 characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
  • G10K11/17821—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 characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the input signals only
  • G10K11/17825—Error signals
• • 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
• • 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
  • G10K2210/129—Vibration, e.g. instead of, or in addition to, acoustic noise
• • 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
  • G10K2210/301—Computational
  • G10K2210/3025—Determination of spectrum characteristics, e.g. FFT
• • 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
  • G10K2210/301—Computational
  • G10K2210/3045—Multiple acoustic inputs, single acoustic output

Definitions

• the present invention relates to active cancellation of noise or vibrations.
• an active vibration cancellation system including means responsive to a residual vibration signal to produce an electrical signal representative thereof, sampling means for sampling said electrical signal and a fourier transformer means for processing the sampled electrical signal to produce a frequency domain representation of the residual vibration signal, wherein the fourier transformer means performs a moving discrete fourier transformation on the sampled electrical signal to produce said frequency domain representation of the residual vibration signal.
• the frequency domain representation is only a partial representation.
• the partial representation may comprise a limited number of, possibly predetermined, harmonics. This avoids the need for unnecessary processing where a particulax noise source includes only a limited number of harmonics which need to be suppressed.
• Figure 1 is block diagram of a single-input/ single-output system according to the present invention
• Figure 2 is a block diagram of a first embodiment of a multi-input/multi-output system according to the present invention
• Figure 3 is a block diagram of a second embodiment of a multi-input/multi-output system according to the present ivnention.
• a source of noise such as an internal combustion engine
• a loudspeaker 3 generates secondary vibrations s which interact with the primary vibration p in the neighborhood of the microphone 2.
• the microphone 2 outputs an electrical signal r which represents the residual sound wave produced by the interaction of the primary vibrations p and the secondary vibrations s.
• the filter 2 is amplified by an amplifier 10 filtered by a low pass filter 11.
• the filter output is then digitised by an A to D converter 4 to produce a signal r' at 15 which is transformed into the frequency domain by a first fourier transformer 5.
• An electrical signal representing the fourier coefficients of the signal r' is fed to a processor 6.
• the processor 6 also receives a synchronisation signal from a synchronisation signal generator 7 which generates the signal synchronisation signal in dependence on the operation of the internal combustion engine 1.
• the fourier coefficients received by the processor 6 are modified in a manner described hereinafter to provide modified fourier coefficients which are fed to a second, inverse fourier transformer 8.
• the second fourier transformer generates a digital time domain signal s ' at 16 in dependence upon the fourier coefficients supplied to it.
• a D to A converter 9 constructs an analog signal from the digital time domain signal.
• the constructed analog signal is filtered by a low pass filter 13, amplified by an amplifier 14 and fed to the loudspeaker 3 which produces the secondary vibrations s in accordance therewith.
• the operation of the processor 6 is such that the secondary vibrations s will tend to be equal in amplitude but opposite in phase to the primary vibrations p in the neighbourhood of the microphone 2.
• the operation of the first fourier transformer 5 will now be described in more detail.
• ⁇ t is selected such that the Nyquist criterion is satisfied for the highest frequency harmonic of interest.
• Rm ( k+l ) [ r* R . ("") "_ r r k , ⁇ + ⁇ r. W ⁇ W
• Equation (2) is known from "Efficient DFT-Based Model Reductions for Continuous Systems", IEEE Transactions on Automatic Control, vol. 36, No. 10, ppll88-1193 and "On-Line Determination of Reduced-Order Models of Linear Systems Via the Moving Discrete Fourier Transform (MDFT)", ICAS "89, ppl796-1799.
• MDFT Moving Discrete Fourier Transform
• ICAS 89, ppl796-1799
• a system embodying the present invention responds to a rapid change in the primary vibrations by producing a smooth decay in the resultant residual signal rather than the stepped decay found with the prior ar .
• the transfer function of the path between the output 16 of the second fourier transformer 8 and the input 15 of the first fourier transformer 5 is stored for use by the processor 6.
• the transfer function may be predetermined or dynamically determined by the processor from detected changes in the signal r' in response to known changes in the signal s ' .
• the transfer function of the path between output 16 of the second fourier transformer 8 and input 15 of the first fourier transformer 5, TF can be defined as follows:
• a is the amplitude change of the sine components - 10 - of the signal s'
• b is the amplitude change of the cosine component of the signal s'
• m is the resultant amplitude in the sine component of the signal r'
• n is the amplitude change in the cosine component of the signal ⁇ r 1 .
• the processor 6 receives the fourier components from the fourier transformer 5 and calculates the necessary change in fourier components of the signal s' based thereon and on the known transfer function of the path between the output 16 of the second fourier transformer 8 and the input 15 of the first fourier transformer 5.
• the fourier components of the changed signal s' are then fed to the second, inverse fourier transformer 8 in order to produce a digital time domain signal, which, after conversion to analog form by the D to A converter 9, is used to produce the cancelling signal s to effect cancellation.
• a two channel system is shown wherein a plurality of microphones 22 are associated with respective loudspeakers 23, for instance in the headrests of the seats in an airliner.
• Each of the microphones 22 is coupled to a respective analog to digital converter 24 via perspective amplifiers 30 and low-pass fitters 31.
• the first fourier transformer 5, operating in accordance with a MDFT algorithm, receives signals from the analog to digital converters 24 and outputs electrical signals representing the fourier coefficients of the signals r' at the inputs to the first fourier transformer 5, which are derived from the residual signals r detected by the microphones 22, to the processor 6. Since each microphone 22 is substantially only affected by its associated speaker 23, the processor 6 operates as described hereinbefore, carrying out the necessary processing of each signal r' independently.
• the modified fourier coefficients are fed to a second fourier transformer 8 which outputs time domain signals to respective digital to analog converters 29.
• the analog signals created by the digital to analog converters 29 are then passed through respective low-pass fitters 32 and amplifiers 33 to the speakers 13.
• FIG. 3 which shows a third embodiment of the,, present invention, suitable for cancelling noise within a volume such as the cabin of a car
• a plurality of microphones 42 are distributed about a volume in which noise is to be cancelled.
• a similar number of loudspeakers 43 are also distributed around the volume.
• the arrangement of microphones 42 and speakers 43 is such that each microphone 42 is influenced by more than one of the loudspeakers 43.
• the outputs from the microphones 42 are again amplified and filtered by amplifiers 50 and low-pass filters 51 and then digitised by respective analogue to digital converters 44.
• a time division multiplexer 40 is interposed between the analogue to digital converters 44 and the first fourier transformer 5.
• the first fourier transformer operates in accordance with a MDFT algorithm.
• the signals output by the first fourier transformer 5 are again passed to a processor 6.
• the processor 6 processes these signals taking into account the fact that each microphone 42 responds to more than one speaker 43. The operation of the processor 6 will be described
• the modified fourier coefficients output from the processor 6 are treated in substantially the same manner as described with reference to Figure 2.
• a demultiplexer 31 is interposed between the second fourier transformer 8 and the digital to analog converters 49.
• the constructed analog signals output from the digital to analog converters 49 are filtered and amplified by respective low-pass filters 52 and amplifiers 53.
• the processor 6 determines the desired change in the signals s ' at the output of the second fourier transformer 8, according to the following algorithm:
• the first row of the transfer function atric contains "the transfer functions of the paths including speaker 1 and respectively each of the microphones 1 to j.
• the functions of the fourier transformers 5, 8 and the processor 6 may be combined, for instance into a microcomputer running under the control of a suitable program.
• the present invention has been described with reference to an internal combustion engine, microphones and loudpseakers, the present invention may be employed to cancel the noise or other cyclic vibrations from various signals and that other forms of transducers may be used in place of microphones and loudspeakers.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Multimedia (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)

Applications Claiming Priority (3)

Publications (2)

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Family Applications (1)

Country Status (4)

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• 1993
  • 1993-04-09 CA CA002117803A patent/CA2117803A1/en not_active Abandoned
  • 1993-04-09 WO PCT/US1993/003354 patent/WO1993021688A1/en not_active Application Discontinuation
  • 1993-04-09 EP EP93909299A patent/EP0697149A1/de not_active Withdrawn
  • 1993-04-09 AU AU39764/93A patent/AU3976493A/en not_active Abandoned

Non-Patent Citations (2)

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