EP0567061A1 - Method and system for reproducing audio frequencies - Google Patents

Method and system for reproducing audio frequencies Download PDF

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Publication number
EP0567061A1
EP0567061A1 EP93106371A EP93106371A EP0567061A1 EP 0567061 A1 EP0567061 A1 EP 0567061A1 EP 93106371 A EP93106371 A EP 93106371A EP 93106371 A EP93106371 A EP 93106371A EP 0567061 A1 EP0567061 A1 EP 0567061A1
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EP
European Patent Office
Prior art keywords
loudspeaker
response
filter
frequency response
cabinet
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP93106371A
Other languages
German (de)
English (en)
French (fr)
Inventor
Aki Dr. Mäkivirta
Juha Kuusama
Minna Juhola
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nokia Technology GmbH
Original Assignee
Nokia Technology GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nokia Technology GmbH filed Critical Nokia Technology GmbH
Publication of EP0567061A1 publication Critical patent/EP0567061A1/en
Withdrawn legal-status Critical Current

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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
    • H04R3/04—Circuits for transducers, loudspeakers or microphones for correcting frequency response
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R29/00—Monitoring arrangements; Testing arrangements
    • H04R29/001—Monitoring arrangements; Testing arrangements for loudspeakers

Definitions

  • the present invention relates to a method for reproducing audio frequencies in a sound reproduction system comprising at least one loudspeaker mounted in a loudspeaker cabinet and in which the frequency response of the loudspeaker is equalized with a filter.
  • the invention also relates to a system for implementing the equalization method.
  • multi-way loudspeaker system of prior art involves several problems.
  • the multi-way loudspeaker system requires provision of separate loudspeaker elements for each frequency band.
  • the crossover filtering of the frequency bands requires provision of extra components, and additional installations.
  • Figure 1 presents the audio response 1 of a wideband one-way loudspeaker of the state of art.
  • the loudspeaker the variation range of the amplitude response may even reach 20 dB. Sounds with different frequencies appear at different volumes and the quality of the sound becomes poor.
  • Such a loudspeaker is not appropriate to be installed in a television receiver.
  • US patent number 4 109 107 shows methods for the compensation of errors in the frequency response of a loudspeaker and these methods are based on a parametric model for the loudspeaker.
  • the patent shows correction done in the area of the mechanical resonance of the speaker, compensation of the defects of the cone-air energy transfer characteristic and compensation of possible cone break-up characteristic. These corrections and compensations are dealing with the parameters of the loudspeaker and they do not provide correction of the whole frequency response when the loudspeaker is attached to a cabinet.
  • the speaker-cabinet junction causes additional errors in the frequency response, but US patent 4 109 107 does not deal at all with correction of such errors.
  • the object of the present invention is to implement a wideband one-way loudspeaker covering substantially the entire audio range, whereby the problems generated by multi-way loudspeakers can be avoided and the drawbacks of methods based on a parameter model for the loudspeaker can be avoided. Also the complicated solution of using many bandpass filters to cover the whole frequency band of a wide-band one-way loudspeaker can be avoided.
  • the aim of the present invention is therefore to overcome the above problems and deficiencies and to provide a method and a system for reproducing audio frequencies with which an acceptable sound quality can be achieved.
  • the invention is characterized in that prior to feeding a signal into a wideband one-way loudspeaker reproducing frequencies substantially over the entire audio range, the output of said loudspeaker being an audio signal, the frequency response of the loudspeaker mounted to its cabinet is equalized with a filter, which is a wideband filter also covering substantially the entire audio range, and with the filter an approximate inverse response is implemented in the desired passband of the loudspeaker system comprising said loudspeaker mounted to its cabinet, the inverse response being formed according to a measured frequency response of said loudspeaker system.
  • the invention differs from prior art in that it is implemented by a digital filter, the inverse filter design can be done without iterative measurement procedures, and no characteristics of the corrective inverse filter are previously fixed (such as the frequency bandwidth), as in other methods, but can be determined during the design procedure, implying that the amplitude, phase of the combination of the amplitude and phase responses can be corrected, and also that the frequencies and the extent of the correction can be determined during the design procedure.
  • the loudspeaker response is equalized according to a measured frequency response of the loudspeaker system comprising a one-way loudspeaker mounted to its cabinet, a much better result can be achieved, since the response is based on the actual loudspeaker system response and not on a model for only the speaker.
  • a model is always incomplete, and it does not consider the effect of the speaker-cabinet junction and the acoustic interaction of the cabinet and the speaker, which are considered in the method and system of the present invention.
  • the system according to the invention comprises a digital filter with which a wideband, one-way audio system can be designed using one conventional loudspeaker element.
  • Figure 2a presents an example of the amplitude response of the equalization filter of the invention.
  • the amplitude response is designated by numeral 2.
  • the imperfections of the amplitude response of an individual loudspeaker element is compensated with the aid of a digital filter.
  • a system and a program for designing equalization filters to implement the invention have been developed.
  • a real-time equalization filter has been designed and implemented.
  • An equalization filter implementing an amplitude response according to Figure 2a is composed of a FIR filter and of one or more second degree IIR filters of biquand type, connected in cascade.
  • the filter may, in fact, be implemented in a number of ways, and the essential feature is that the filter is a digital filter, preferably a filter including FIR and/or IIR filters.
  • the frequency response of a one-way loudspeaker system comprising a one-way loudspeaker mounted in its cabinet is first measured. On the basis of the measurement result the properties for the equalization filter are established. On the basis of the measurements and requirements set for a loudspeaker, an inverse filter can be designed for equalizing the variations of the frequency response of a loudspeaker.
  • the response is averaged by using an averaging method. In that case the averaging method averages the measured response in the frequency domain and the inverse response is then formed from this averaged response.
  • a FIR filter was first designed in which the response is an inverse of the amplitude response of the loudspeaker system between selected frequencies, the intended passband of the system.
  • Low sound frequencies i.e. frequencies below 1.5 kHz, were equalized using second-order filter blocks.
  • the bass response was expanded by one second-order filter block.
  • the length of the FIR filter was 91, and three second-degree filter blocks were implemented with all-pass filters were used therein.
  • a digital filter can convenienty be implemented with a digital signal processor.
  • the sufficient calculation rate of a digital signal processor is about 10 MIPS.
  • the processor must in such a case have at least 16 bit word lentgh.
  • Such processors are readily available on the market.
  • the dynamic range of the equalization filter was about 15 dB, see amplitude response in Fig. 2a.
  • Figure 2b illustrates an embodiment of the invention in a sound reproducing system, such as a TV set.
  • the wideband filter 4 according to the invention covering substantially the desired audio range and being a digital filter, can be implemented in a digital signal processor 4b programmed to implement a desired transfer function, i.e. frequency response 2 which is an inverse of the frequency response 1 of the loudspeaker system comprising a loudspeaker 5 mounted in its cabinet (not shown) and is connected to a digital sound processing circuit 4a of the sound reproduction system (here, a digital television sound processing circuit).
  • a desired transfer function i.e. frequency response 2 which is an inverse of the frequency response 1 of the loudspeaker system comprising a loudspeaker 5 mounted in its cabinet (not shown) and is connected to a digital sound processing circuit 4a of the sound reproduction system (here, a digital television sound processing circuit).
  • the digital sound processing circuit 4a processes tone, volume, balance, and some other controls of the stereo sound and usually includes DA converters with which the sound signal is converted from the digital into the analog form for the loudspeaker 5.
  • the sound processing circuit 4a and the digital signal processor 4b (implementing the actual filtering according to the invention) may constitute one part 4.
  • Information i.e. the sound in digital format
  • the filter 4 can be positioned in the sound reproduction system e.g.
  • a signal IN entering the processing system is a signal from the intermediate stage of a tuner, such as the TV tuner, and an the processed and equalized analog sound signal OUT obtained from the filter 4 is, prior to being fed to the loudspeaker 5, be processed in a final amplifier stage.
  • Figure 3 presents the response of a one-way loudspeaker after equalization.
  • the audio response is designated by a numeral 3.
  • the amplitude response of the equalized loudspeaker is acceptable.
  • the range of amplitude response variation of the original one-way loudspeaker was about 20 dB (see Fig. 1).
  • the amplitude response variation of the equalized loudspeaker was about 6 dB for frequencies below 6 kHz, and in the entire passband, below 10 dB.
  • the sound quality of the system equalized according to the invention was better than in a state-of-the-art multi-way loudspeaker systems.
  • the audio power produced by the frequency equalized one-way loudspeaker was adequate. The sound appeared natural and did not contain any strong colourings.
  • the objective and subjective quality of sound of the system according to the invention was at least as good as in state-of-the-art receivers. Thanks to the invention, the power response of the loudspeaker, i.e. the power radiation pattern, can be optimized economically and much more carefully when only one element is used.
  • the amplitude response problems caused by crossover filtering and concurrent radiation from several loudspeaker elements can be avoided. Also the efficiency of the sound reproduction is increased when components consuming power in the crossover filter can be eliminated.
  • This invention makes it possible to obtain a good sound quality by using only one loudspeaker element.
  • One loudspeaker element is easier to install than several. No crossover filtering is needed.
  • the mechanical structure of the receiver is simplified and assembly facilitated. This results in cost savings in series production.
  • the method suggested by the invention can be used not only for equalizing the amplitude response as in the above examples but also for equalizing also the phase response, or the combination of the amplitude and the phase responses.
  • a one-way loudspeaker for equalizing the frequency response of a one-way loudspeaker, whereby a uniform frequency response is achieved with a one-way loudspeaker substantially in the entire audio frequency range, preferably between frequencies 50 Hz to 20 kHz, depending on the sound reproduction system.
  • the method and the system can be used in various sound reproduction systems, such as in television sets, particularly in digital TV sets, in sound reproduction amplifiers, telephone sound reproduction, etc.
  • the reproduced frequency range in TV sets is usually from 100 Hz to 16 kHz, in telephones from 500 Hz to 4 kHz, and in HiFi systems from 50 Hz to 20 kHz.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Circuit For Audible Band Transducer (AREA)
EP93106371A 1992-04-23 1993-04-20 Method and system for reproducing audio frequencies Withdrawn EP0567061A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI921817 1992-04-23
FI921817A FI921817A (fi) 1992-04-23 1992-04-23 Foerfarande och system foer aotergivning av audiofrekvenser

Publications (1)

Publication Number Publication Date
EP0567061A1 true EP0567061A1 (en) 1993-10-27

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Family Applications (1)

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EP93106371A Withdrawn EP0567061A1 (en) 1992-04-23 1993-04-20 Method and system for reproducing audio frequencies

Country Status (2)

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EP (1) EP0567061A1 (fi)
FI (1) FI921817A (fi)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0762801A2 (en) * 1995-09-01 1997-03-12 Speaker Array Logic, Inc. Non-directional speaker system with point sound source
WO2000064217A1 (de) * 1999-04-19 2000-10-26 Siemens Aktiengesellschaft Flächenlautsprecher und verfahren zu dessen betrieb
CN102301742A (zh) * 2009-01-30 2011-12-28 杜比实验室特许公司 用于从临界带化的脉冲响应数据确定逆滤波器的方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0168078A1 (en) * 1984-06-08 1986-01-15 Koninklijke Philips Electronics N.V. Arrangement for converting an electric signal into an acoustic signal or vice versa and a non-linear network for use in the arrangement
US4888811A (en) * 1986-08-08 1989-12-19 Yamaha Corporation Loudspeaker device
WO1991002407A1 (en) * 1989-08-11 1991-02-21 Bell Communications Research, Inc. Wideband digital equalizers for subscriber loops

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0168078A1 (en) * 1984-06-08 1986-01-15 Koninklijke Philips Electronics N.V. Arrangement for converting an electric signal into an acoustic signal or vice versa and a non-linear network for use in the arrangement
US4888811A (en) * 1986-08-08 1989-12-19 Yamaha Corporation Loudspeaker device
WO1991002407A1 (en) * 1989-08-11 1991-02-21 Bell Communications Research, Inc. Wideband digital equalizers for subscriber loops

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0762801A2 (en) * 1995-09-01 1997-03-12 Speaker Array Logic, Inc. Non-directional speaker system with point sound source
EP0762801A3 (en) * 1995-09-01 1998-05-20 Speaker Array Logic, Inc. Non-directional speaker system with point sound source
WO2000064217A1 (de) * 1999-04-19 2000-10-26 Siemens Aktiengesellschaft Flächenlautsprecher und verfahren zu dessen betrieb
CN102301742A (zh) * 2009-01-30 2011-12-28 杜比实验室特许公司 用于从临界带化的脉冲响应数据确定逆滤波器的方法
CN102301742B (zh) * 2009-01-30 2014-04-09 杜比实验室特许公司 用于从临界带化的脉冲响应数据确定逆滤波器的方法

Also Published As

Publication number Publication date
FI921817A (fi) 1993-10-24
FI921817A0 (fi) 1992-04-23

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