Classifications

• • 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
• • 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
  • H04R7/00—Diaphragms for electromechanical transducers; Cones
  • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
  • H04R7/04—Plane diaphragms
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R7/00—Diaphragms for electromechanical transducers; Cones
  • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
  • H04R7/04—Plane diaphragms
  • H04R7/045—Plane diaphragms using the distributed mode principle, i.e. whereby the acoustic radiation is emanated from uniformly distributed free bending wave vibration induced in a stiff panel and not from pistonic motion

Definitions

• the invention relates to a flat-panel loudspeaker ge ⁇ Gurss to the preamble of claim 4 and a method for its operation according to the preamble of claim 1.
• Area speakers of the type mentioned have long been known as such, for example from DE patent 484 872.
• a voice coil that works according to the electrodynamic principle is used, which is placed directly on a surface - initially of any size and thickness and made of a selected material - and mechanically fixed there. If the voice coil is excited electrically by a sound generator, its vibrations are transmitted to the surface acting as a membrane and thus used as a sound-radiating surface.
• a multitude of possible uses would exist for an electroacoustic transducer of this type. If, with a few exceptions, it has not yet become widely accepted, this is due to its electroacoustic properties, in particular its transmission function.
• the sound-radiating surface with its mechanical properties is the main function. This surface can only transmit tones or sounds if it vibrates mechanically. Apart from the clamping, ie the mechanical mounting and the location of the voice coil on it, a plate-shaped surface, which is preferably excited to bending vibrations, is in itself a relatively complex structure in terms of its vibration behavior. While a commercially available loudspeaker based on the electrodynamic principle is still largely in hand, even if only with compromises, the sound-emitting membrane is in view To optimize their acoustic properties, this is not easily possible with surface speakers.
• Illu ⁇ is strated this problem on an example is placed If the glass surface of a display window on which a voice coil, are used as flat-panel loudspeaker, so are the material, shape and dimensions of the sound-emitting surface, also its clamping substantially fixed.
• the frequency response of the area loudspeaker in this example is thus essentially predetermined.
• the natural resonances of the surface used for sound radiation with this material and the dimensions of the shop window result in a frequency response which - simplified - can be described by an excessive reproduction in the range of low tones and also by a tendency to distortion that affects the influence of those still in the listening range Natural resonances of higher order can be attributed. Corresponding characteristic non-linearities also occur with other materials, such as wood or plastic materials.
• the invention is therefore based on a first subtask, using a method of the type mentioned at the beginning, to specify a way by which the non-linearities in the frequency response of the surface speakers can be mastered at least to such an extent that its sound spectrum appears sufficiently natural for the respective application.
• a second subtask is to use a surface loudspeaker at the beginning using such a method named kind, the electro-acoustic properties inherent ⁇ - depending on the application - are optimized so that fulfills the quality of a sound thus carried out in the individual application requirements specified advertising to.
• a flat-panel loudspeaker is not like a loudspeaker box composed of individual, individually designed loudspeaker units. His development to date has shown that approaches that have failed to achieve a satisfactory result by means of constructive measures to improve the area loudspeaker have shown.
• the invention frees itself from conventional considerations of the electro-acoustician and takes a different path.
• the elektroaku ⁇ stica properties of the surface of the speaker are set by the sum of the characteristics of the voice coil (s) used and the mechanical properties of the sound- strehl tract employed. For each arrangement of a surface loudspeaker determined in this way, its electroacoustic transfer function in the form of its frequency response - apart from tolerances - is defined.
• the frequency response of the surface loudspeaker can be compensated for and thus linearized with a filter device arranged in the operating arrangement of the surface loudspeaker between the sound source and the amplifier located in front of the voice coil or the voice coils, provided that the transfer function of the Filter device is essentially inverse to the corresponding function of the combination of voice coil (s) and sound-emitting surface.
• the transfer function of the filter device is simulated by digital filters, in particular by FIR (Finite Impulse Response) filters, the filter coefficients of which are derived from the inverse frequency curve of the surface loudspeaker.
• FIR Finite Impulse Response
• the filter device preferably has, as an input element, a sample / hold element, which is connected to the digital filter via an analog-to-digital converter, the output of which is connected to a digital-to-analog converter.
• the filter device is equipped with a digital signal processor.
• Digital signal processors are used on a large scale today and, due to the progress made in the development of integrated circuits, are also suitable for immersive "real-time" applications already available.
• Digital Si ⁇ are gnalreaoren, albeit to a limited extent of the available volume for the program memory, freely programmable. This makes it possible, the function of the digital signal processor to different materials of the sound-emitting surface In addition, different outlines of the sound-radiating surface can be realized in this way.
• FIG. 1 shows a surface loudspeaker in connection with a measuring arrangement for measuring its frequency response
• FIG. 2 shows a first embodiment of a circuit arrangement for operating the surface loudspeaker
• FIG. 3 shows a further embodiment of the circuit arrangement according to FIG. 2.
• 1 shows a flat-panel loudspeaker 1 is schematically shown, a plate-shaped, schallabstrah ⁇ loin area 2 has, on the example of two Schwingspu ⁇ len are arranged 3 and 4 respectively.
• the voice coils 3 and 4 are mechanically fixed on the sound-radiating surface 2 in such a way that, in the electrically excited state, they transmit their mechanical vibrations that occur to the sound-radiating surface 2 so that they themselves excite to vibrate and thus to emit sound.
• the voice coils 3, 4 are connected in parallel to the outputs of an amplifier 5, the input of which is coupled to a sound source (not shown in FIG. 1) during normal operation.
• a frequency analyzer 6 which, at a tunable frequency with a predetermined level, outputs a defined electrical measurement signal to the amplifier 5 and, via the voice coils 3, 4, the surface loudspeaker 1 stimulates sound radiation.
• a measurement microphone 61 which is connected to the input of the frequency analyzer 6, is arranged at a defined distance from the surface loudspeaker 1, preferably along its central axis.
• the frequency response of the test object is determined with this measuring arrangement, which is preferably set up in an anechoic room in order to reproduce the sound propagation in the free field as precisely as possible under measurement conditions.
• this frequency response in the area loudspeaker 1 is determined by object-typical non-linearities, which is why it must be measured individually at least for each object type. This gives the flat panel loudspeaker 1 an essential measure of its electroacoustic transmission properties. In order to compensate for the non-linearities of the frequency response, the inverse function of the frequency curve obtained in this way is formed.
• FIG. 2 shows schematically, using an operating circuit for the surface loudspeaker 1, how the measurement result described is used to equalize the transmission properties of the special electroacoustic transducer.
• the sound source is exemplified by a magnetic tape device 7. Its output is connected to the amplifier 5 of the surface loudspeaker 1 via a filter device 8.
• a transfer function is implemented which corresponds to that for this type of surface loudspeaker 1 measured, characteristic frequency curve in wesentli ⁇ chen-inverse.
• the course of the transfer function of the filter device 8 is to be approximated to the inverse frequency curve of the surface loudspeaker 1, the higher the demands placed on the resulting transmission quality of the surface loudspeaker 1 in the respective application.
• the electrical audio signals supplied by the magnetic tape device 8 are predistorted in a manner which is just opposite to the frequency response of the flat-panel loudspeaker 1.
• This predistorted sound signal is fed to the voice coils 3, 4 of the surface loudspeaker 1 via the amplifier 5.
• it is converted into acoustic signals in the flat panel loudspeaker 1, it is equalized again due to its transfer function.
• the resulting frequency response of the flat-panel loudspeaker 1 is linearized the better, the closer the transfer function of the filter device 8 approaches the inverse frequency curve of the flat-panel loudspeaker 1.
• electrical filters can also be constructed from discrete elements; however, complex transfer functions for a bandpass filter in the audible range, such as occur in this area of use in conjunction with flat-panel loudspeakers 1, can be implemented with discrete components only with great effort and then only in a first approximation. Realizations of the filter device 8 with discrete components are therefore only suitable in connection with a surface loudspeaker 1 if, in individual cases, only limited demands are placed on its transmission quality.
• FIG. 3 therefore shows a further embodiment for the operating circuit of an area loudspeaker 1, with which even HiFi (high fidelity) requirements can be met.
• the embodiment according to FIG. 3 differs from the embodiment according to FIG. 2 in the further configuration of the filter device 8.
• the filter device 8 is shown as a digital filter. Its on the re-specified as an example of a sound source Ma ⁇ gnetband réelle 7 connected input circuit is palpable as a shut-off / holding member 9 - often referred to as "Sample and Hold" - refers circuit -.
• the gnetband réelle from ma- 8 supplied as an analog signal electrical sound signal sampled according to a predetermined sampling theorem, the sampled instantaneous value temporarily stored and fed to an analog-to-digital converter 10 connected to it, which converts the successive instantaneous values into digital signals expressed in binary form, in which the signals are fed to a digital signal processor 11.
• the output side is the digital signal processor 11 connected to a digital-to-analog converter 12, with which its binary output signal is converted back into an analog electrical signal, which is fed to the surface speaker 1 via the amplifier 5.
• This configuration of the filter device 8 takes advantage of the advances in the development of digital signal processing.
• the semiconductor industry today offers users powerful, widely used signal processors for "real-time” applications. Possible uses of digital signal processors and configurations with appropriate programs can therefore be assumed to be known here.
• the schematic illustration in FIG. The structure of the digital signal processor is not specified in detail, and in addition to a microcontroller, the actual control unit, a signal processor usually has a program, a data and an input / output memory which are connected to one another via a bus system with parallel address, control and data lines.
• the possibility of storing a specific program in the program memory, which relates to the respective application improves the digital signal processor to a universally usable electronic circuit, which is used in the present field of application is used to emulate the transfer function of the filter device 8.
• the filter or filters in the form of FIR (Finite Impulse Response) filters, which can also be used to implement complex transmission functions for “real-time” requirements in a known manner
• FIR Finite Impulse Response
• the transmission quality of the flat-panel loudspeaker 1 has very high requirements, such as HiFi quality, so it may be necessary due to the necessary signal processing under real-time conditions to carry out this signal processing in parallel operation of several signal processors without leaving the basic solution.
• the embodiments described above open up a wide range of applications for the flat panel loudspeaker.
• the free programmability of the digital signal processor 11 allows the effort for the measurement of the frequency response of the respective type of surface loudspeaker 1 and the conversion of the measured frequency curve into a more or less approximate inverse transfer function of the filter device 8 with regard to the respective application to optimize.
• Small, but also large-format area loudspeakers can be realized. Since the selection of materials in a surface loudspeaker designed according to the invention is no longer subject to the conventional limitation, it is also possible, for example, to select materials with a very low specific weight for the sound-emitting surface.
• Panel loudspeakers according to the invention can therefore be used both for commercial purposes, such as public sound reinforcement systems, and also for advertising surfaces, such as in the personal area, as high-quality, very flat loudspeaker units which are integrated, for example, in furniture.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Multimedia (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Circuit For Audible Band Transducer (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
• Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=7905046

Family Applications (1)

Country Status (7)

Cited By (2)

Families Citing this family (6)

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• 1999
  • 1999-04-19 DE DE19917584A patent/DE19917584A1/de not_active Withdrawn
  • 1999-10-21 WO PCT/DE1999/003377 patent/WO2000064217A1/fr active IP Right Grant
  • 1999-10-21 DK DK99960797T patent/DK1169884T3/da active
  • 1999-10-21 AU AU17687/00A patent/AU767985B2/en not_active Ceased
  • 1999-10-21 EP EP99960797A patent/EP1169884B1/fr not_active Expired - Lifetime
  • 1999-10-21 AT AT99960797T patent/ATE243910T1/de active
  • 1999-10-21 JP JP2000613226A patent/JP2002542745A/ja active Pending
  • 1999-10-21 DE DE59906131T patent/DE59906131D1/de not_active Expired - Lifetime

Non-Patent Citations (1)

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