EP1569497A1 - Lautsprecher mit Bewegungsrückkopplung - Google Patents

Lautsprecher mit Bewegungsrückkopplung Download PDF

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Publication number
EP1569497A1
EP1569497A1 EP04004207A EP04004207A EP1569497A1 EP 1569497 A1 EP1569497 A1 EP 1569497A1 EP 04004207 A EP04004207 A EP 04004207A EP 04004207 A EP04004207 A EP 04004207A EP 1569497 A1 EP1569497 A1 EP 1569497A1
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EP
European Patent Office
Prior art keywords
coil
light
moving
detection system
diaphragm
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Withdrawn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
EP04004207A
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English (en)
French (fr)
Inventor
Hans-Jürgen Regl
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Harman Becker Automotive Systems GmbH
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Harman Becker Automotive Systems GmbH
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Filing date
Publication date
Application filed by Harman Becker Automotive Systems GmbH filed Critical Harman Becker Automotive Systems GmbH
Priority to EP04004207A priority Critical patent/EP1569497A1/de
Publication of EP1569497A1 publication Critical patent/EP1569497A1/de
Withdrawn legal-status Critical Current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
    • H04R3/002—Damping circuit arrangements for transducers, e.g. motional feedback circuits

Definitions

  • This invention relates to detection systems and methods for detecting the position and/or movement of loudspeakers, methods for reducing acoustic distortions in sound systems and such sound systems. More particularly, this invention relates to detection systems using optical distance, speed, and velocity measurement technologies, and to electro-dynamic sound systems that employ the motion feedback control technique to improve the sound fidelity by reducing the acoustic distortions in the lower frequency range.
  • an electro-dynamic sound system employing the motion feedback control detects vibration, or movement, of a vibrating system of the sound system such as its diaphragm or coil carrier, and sends this vibration back to an amplification circuit to form a negative feedback for driving the vibrating system. It is thereby possible with this type of sound system to reproduce audio signals with high fidelity.
  • the motion feedback control technique requires, in general, sensor signals that encode information about the current motional condition of a loudspeaker such as the position, the speed, and/or the acceleration of the diaphragm or the coil carrier.
  • the knowledge of one or more of these values allows a correction signal to be calculated as the feedback. Then, by superimposing this correction signal onto the original input signal to the sound system, a feedback loop is completed and in turn a lower distortion achieved for the sound system.
  • the detection of the movement and/or position of the diaphragm or the coil carrier and the generation of sensor signal(s) are accomplished through one of the following conventional means:
  • US application publication US 2003/00724622A1 discloses the usage of two sensors, a position sensor and an acceleration sensor to detect the movement of the voice coil of a loud speaker and in turn to generate feedback control signals.
  • these two sensors and their corresponding feedback networks are complicated electrical circuits and therefore prone to variations in environmental conditions such as acoustic venues, temperatures, and air densities in the loudspeaker.
  • US patent 4,573,189 to Hall proposes feedback means for a loudspeaker including a small motion sensing element, such as an accelerometer, mounted on the voice coil. This mechanism suffers from, as admitted by the inventor himself, a significant low frequency instability of the feedback loop.
  • US-Patent 4,727,584 proposes an improvement to the motional feedback technique by enclosing the accelerometer in an air-tight shield. This solution nevertheless results in an increased mass weight of the loudspeaker thereby effecting speaker characteristic.
  • optical distance measurement techniques Two well known examples of these optical distance measurement techniques are 1) reflected light intensity, based on light reflection, and 2) laser triangulation, based on diffraction, interference, and laser technology.
  • optical motional feedback loudspeaker is known from the published French patent application 2296985, Japanese utility model 4215110, US patent 4,207,437, etc.
  • these systems comprise two elements, a light source and a detector, at least one of those elements being connected to the magnet system, and the detector supplying a voltage which substantially corresponds to the displacement of the diaphragm.
  • DSP digital signal processing
  • This invention improves loudspeakers and sound systems by providing an optical detection system that comprises a transmitter, that is, a light source, an optical structure for either reflecting or letting pass the light from the transmitter, and a receiver constituting at least one photo-sensor for sensing the light that is reflected or is passed by the optical structure and generating electrical signals accordingly.
  • Said optical detection system may include an additional light conducting system for ensuring that the light from the transmitter is focused onto the optical structure as a small dot or bar.
  • the optical structure is constructed on the moving-coil system of the sound system while the transmitter and the photo-sensor on some non-moving part thereof.
  • This detection system works in this way: when the diaphragm and/or the coil carrier vibrates, the optical structure vibrates along; this motional change is then sensed by the photo-sensor and converted into electrical signals accordingly.
  • the movement, the speed, the velocity, and/or the position of the diaphragm or the coil carrier can be detected and translated into motion correction signals.
  • the optical structure used in the detection system employs optical technologies that can measure distance, speed, and velocity in a highly economical way and facilitate digital signal encoding.
  • the optical structure is made up of light-passing or absorbing and/or light-reflecting optical segments, which preferably form a certain periodical pattern.
  • a focused beam of light originated from the transmitter is either absorbed or reflected by the segments in the pattern and, accordingly, the photo-sensor reacts to either the transmitted light or the reflected light from the optical structure.
  • the optical structure moves, the light reaching the photo-sensor is interrupted by the positional changes of the segments modulated with a frequency corresponding to the velocity of the optical structure.
  • the sensor Whenever the light is interrupted, the sensor generates a signal to indicate a certain amount of movement of the optical structure. Since the optical structure is fixed on the moving coil system of the sound system, this detected movement is therefore the movement of the diaphragm or the coil carrier. While a periodical optical pattern is often a necessary feature for the optical structure in the "line grid” method, it is however not required in another optical distance/speed/velocity detection technology, called “2D-array-based," in which the optical structure can be any surface that has a certain amount of optical "roughness.” In the "2D-array-based” scenario, a transmitter casts light onto the optical structure which reflects that light as a patch of image onto a multiple array of photo-sensors.
  • the sensors reacting to optical stimulus at a certain rate, for example, 500 pictures per second, send each image to a signal processor for analysis.
  • the signal processor detects patterns in the images and "sees" how those patterns have moved since the previous image. Based on the change in the patterns over a sequence of images, the signal processor determines how far the optical pattern has moved in various dimensions.
  • optical distance/speed/velocity detection technologies have many advantages. Firstly, they are easy and inexpensive to implement. Secondly, they are robust due to their immunity to the variation in the environmental conditions. Last but not least, they provide possibilities to output measurement signals in the digital form.
  • This sound system comprises a diaphragm for producing the acoustic wave, a driving system for driving this diaphragm in response to an input signal, with this driving system comprising a moving-coil system which further comprises a coil carrier mounted on the diaphragm and a voice coil wound about the coil carrier and connected to receive the input signal, and a magnet assembly for producing a magnetic field for generating the driving power driving the diaphragm along with the moving-coil system, an optical detection system as mentioned above for detecting the motion, speed, and/or position of the diaphragm or the moving-coil system, and a signal processing circuitry for at least interconnecting the driving system and the detection system, processing the electric signals from the detection system into a motion correction signal, mixing such motion correction signal with the input signal, and feeding the resultant mixed signal to the driving system.
  • the electrical signals output from the detection system are processed into a motion correction signal which is to be fed-back into the sound system.
  • the complete sound system 10 in the present invention comprises, among other parts, three major components: a driving system 16, a detection system 18, and a signal processing circuitry 20.
  • the motion feedback control process of the sound system works as follows: initially, the input terminal 12 receives an input signal e i representing the sound signal to be reproduced; next, e i is applied to a mixing point 14, which mixes the signals coming in and outputs signal e c to drive the driving system 16 of the sound system and thereby cause the diaphragm and the coil carrier to vibrate; then, the detection system 18 detects the motion of the diaphragm or the coil carrier and produces motion signals e o accordingly; after that, e o is input to the signal processing circuitry 20 where e o is processed into a motion correction signal e f ; finally, e f is fed back to the mixing point 14 to be mixed with the input drive signal e i to form the corrected input signal e c .
  • the driving system comprises a moving-coil system and a magnet assembly.
  • the moving-coil system includes a voice-coil 26 wound about a cylindrical coil carrier 24 which is mounted on the base 22 of the diaphragm (not otherwise shown). Since connected together, the diaphragm and the coil carrier move along with each other.
  • the magnet assembly is to produce a magnetic field for generating the driving power to drive the based 22 of the diaphragm.
  • An example of the magnet assembly is a ring magnet 30 with pole pieces 32 and 33.
  • a conventional spider 28 holds the voice-coil in proper alignment as it moves in the air gap 34 of the magnet. All the above elements are conventional in the art.
  • Figures 3 and 4 concern the details of the detection system of the present invention.
  • Figure 3 schematically depicts the constituting elements of the detection system while Figure 4 shows how this system can be incorporated into a sound system.
  • the detection system 18 comprises essentially three elements: a transmitter 35 as a light source, an optical structure 36 made up of light-reflecting and/or light-passing/absorbing segments, and a receiver constituting at least one photo-sensor 37.
  • the basic principle of the optical detecting is as follows: the light generated from the transmitter 35 reaches the optical structure 36 and is either reflected back or let pass; depending on the relative positions of these three elements the photo-sensor 37 reacts to either the reflected light from the optical structure 36 or the transmitted light passing through the optical structure, 36 and in turn transforms this optical stimulus into electrical signals.
  • the relative movement of the optical structure against the transmitter and photo-sensor creates moving optical stimulus for the photo-sensor which consequently generates changing electrical signals accordingly.
  • the light from the transmitter should be preferably focused onto the optical structure so that only a small dot or bar is observed on the structure.
  • a laser diode may be used as the transmitter because a laser diode generally emits a focused beam of light.
  • certain light conducting mechanism may be used along the path from the transmitter to the optical structure.
  • a fourth element a light conducting construction, such as fiber optics or a lens system 38, is included in the detection system.
  • Figure 4 shows that how this optical detection system may be incorporated into a sound system.
  • the optical structure 46 is constructed on the moving-coil system of the sound system/loudspeaker, such as on the lateral surface of the coil carrier; the transmitter and the photo-sensor, together labeled as 48, are constructed on some nonmoving part of the sound system, such as inside the coil carrier.
  • the diaphragm or the coil carrier vibrates, the optical structure moves along while the transmitter and the photo-sensor remain stationary.
  • the movement of the optical structure is the movement of the diaphragm and the coil carrier.
  • This movement is detected by the photo-sensor and an electrical signal is generated accordingly. Since the frequency of the electrical signal corresponds to the velocity of the movement, a velocity signal is therefore obtainable.
  • integrating velocity over time gives the distance that the diaphragm or coil carrier has traveled and differentiation gives the acceleration (of the diaphragm or the coil carrier) which corresponds to the generated sound pressure.
  • the position of the diaphragm or coil carrier is also obtained.
  • the photo-sensors may be Charge Coupled Devices (CCD), photo-diodes, photo-transistors, Complementary Metal Oxide Semiconductor (CMOS) sensors, and many more.
  • CCD Charge Coupled Devices
  • CMOS Complementary Metal Oxide Semiconductor
  • the number of the photo-sensors can vary as well: a signal photo-sensor, a pair of photo-sensors, a line array of photos, and a multiple array of photo-sensors.
  • the arrangement of having the optical structure 46 constructed on the moving coil system while both the transmitter and the photo-sensor mounted on some non-moving part of the sound system is sufficient to create an observable relative movement between the optical structure and the transmitter and photo-sensor.
  • a preferred construction site for the optical structure is the lateral surface of the cylindrical coil carrier, especially the inner lateral surface.
  • both the transmitter and the photo-sensor may (preferably) reside inside the coil carrier.
  • one of the transmitter and the photo-sensor should be positioned inside the coil carrier and the other one outside.
  • the fundamental requirement for the optical structure used in the detection system is that the structure is made of segments that are either light-reflecting or light-passing/absorbing.
  • the optical structure may be constructed in a large number of ways. Three optical structures are presented in Figures 5-7 as examples of the "line grid" optical detection system proposed in the present invention. In their respective descriptions, emphasis are placed on the pattern that the segments form, the mechanical construction of the optical structure on the sound system, and the motion/position information that such patterns can convey.
  • an optical structure 48 is made of a set of line segments which are either light-reflective (shown as dark lings 52 in the figure) or light-passing/absorbing (shown as light lines 54 in the figure).
  • the lines are of equal thickness and, therefore, form a wave with the period (P) comprising a pair of dark and light lines.
  • this wave of periodical lines is formed to propagate in parallel to the direction of the movement of the diaphragm or the coil carrier.
  • An optical structure made of a single set of periodical lines as described above allows the speed of the movement to be detected.
  • periodical light-reflective or light-passing/absorbing lines each time the optical structure moves along with the diaphragm or the coil carrier, the beam of light from the transmitter is interrupted by these lines and this interruption is sensed by the photo-sensor. Since these lines are equally thick, the number of interruptions per unit time therefore corresponds to the speed of the movement of the optical structure, or said in another way, the speed of the movement of the diaphragm or the coil carrier.
  • the electrical signals generated by the photo-sensor are encoded with the information of the speed of the diaphragm or the coil carrier.
  • Integrating this speed over time gives the distance that the diaphragm or coil carrier has traveled and differentiation gives the acceleration (of the diaphragm or the coil carrier) which corresponds to the generated sound pressure.
  • the speed, the acceleration, and/or the position of the diaphragm or coil carrier is also obtained.
  • FIG. 6 Another optical structure made of line segments that are either light-reflective or light-passing/absorbing is shown in Figure 6.
  • This optical structure comprises two identical sets of periodical line structures positioned in parallel with a predefined phase shift in their wavefronts. The phase shift is preferred to be a quarter of the wave period.
  • the use of such two sets of line segments along with a pair of photo-sensor enables not only the speed but also the direction of the movement of the optical structure to be detected.
  • the electrical signals generated by the photo-sensors are encoded with the information of the speed and the direction of the movement of diaphragm or the coil carrier.
  • the actual construction of the lines may be achieved in various ways including making periodical grooves into the lateral surface of the coil carrier; attaching a metallic layer onto a plastic foil, printing periodical lines on the metallic layer and then attaching the plastic foil firmly onto the lateral surface o the coil carrier; or many others.
  • integrating the speed over time gives the distance that the diaphragm or coil carrier has traveled and the time derivative is the acceleration.
  • the position of the diaphragm or coil carrier is also obtained.
  • yet another optical structure 48 is shown to be made of light-reflective and light-passing/absorbing line segments, similar to those in the previous two optical structures. These line segments forms a plurality of sets of periodical line structures positioned in parallel with a discretization of n bits. Particularly in Figure 7, there are four sets of periodical line structures with a discretization of four bits.
  • This optical structure may be constructed in the same ways as those described in Figure 6. Therefore, the sets of line structures are preferably attached to the lateral surface of the coil carrier.
  • the set that is attached directly on top the lateral surface is labeled "layer 1" 71 and has a period of P; the set that is attached on top of "layer 1” is called “layer 2" 72 and has a period of P/2; this continues and the "layer 3" set has a period of P/4 and the "layer 4" set P/8.
  • This arrangement of the four sets, together with a line array of four photo-sensors as the receiver facilitates the binary encoding of four bits (as the "0101" shown in the figure), a mechanism that makes possible the detection of the precise position of the diaphragm or the coil carrier.
  • the electrical signals generated by the line array of four photo-sensors are encoded with the position information of the diaphragm or the coil carrier.
  • optical structures described above fall into the "line grid” category of the optical detection
  • an optical structure using the other category, "2D-array-based” is illustrated in Figure 8.
  • the "2D-array-based” technology does not require any periodical pattern to be separately constructed; instead, any surface can be used as the optical structure as long as the surface has a certain degree of optical roughness.
  • a preferred surface is the lateral surface if the coil carrier.
  • the light illuminating the optical structure does not have to be focused into a small dot or bar.
  • the lens system projects the line image onto the detector which can react to the changes in this image.
  • this surface enables a more comprehensive determination of the movement and/or position of the diaphragm or the coil carrier. For instance, movement vectors, positional changes dx and dy, and so on, can all be detected.
  • optical mouse technology such as the article "How do optical mice work?" retrieved from the "Howstuffworks" website. (http://computer.howstuffworks.com/question631.htm)
  • the optical structure in use comprises two identical sets of periodical line structures 86'and 86" positioned in parallel with a phase shift of a quarter of the wave period.
  • the optical structure is attached to the inner lateral surface of the coil carrier, with the sets of line structures propagating in the direction parallel to the axis of symmetry of the coil carrier.
  • the transmitter 82 is a laser diode
  • the receiver a pair of photo-sensors 88'and 88''. Both the laser diode and the photo-sensor reside inside the coil carrier.
  • the laser diode generates a focused beam of light onto the optical structure.
  • the light reflecting lines of the optical structure reflect this incoming light while the light-passing/absorbing ones let it pass.
  • the reflected light from the two sets of line structures 86'and 86" reach the photo-sensors 88'and 88" respectively.
  • the two photo-sensors react to this optical stimulus and generate binary electrical signals as the two square waves shown in this figure. These binary signals allow the speed as well as the direction of the movement of the diaphragm or the coil carrier to be calculated. Integrating the speed over time gives the distance that the diaphragm or coil carrier has traveled and the time derivative is the acceleration. Thus, the position of the diaphragm or coil carrier is also obtained.
  • FIG 10 is the block diagram of a possible analogue signal processing circuitry of the sound system using an optical structure made up of "two sets" of line structures as described in Figure 8.
  • this signal processing circuitry interconnects the driving system and the detection system of the loudspeaker and processes the signal s(t) (encoded with the speed and direction information of the movement of the diaphragm or the coil carrier) from the detection system into a motion correction signal e c (t).
  • the entire process takes a number of steps: First, upon receiving s(t) from the detection system, frequency/voltage conversion (frequency corresponds to velocity) and phase detection are carried out to get the velocity signal v(t). Second, v(t) is taken time derivative to generate the acceleration signal a(t).
  • a(t) is compared with the original input signal e i (t) in order to determine the difference therebetween. Then, this difference, ⁇ e(t), is applied to the mixer 94 which can be, for example, a multiplicator or an adder, and is mixed with the original input signal e i (t) to result in a corrected input signal e c (t). Finally, e c (t) is fed to the driving system of the sound system.
  • This analogue signal processing circuitry may also be realized in digital technology.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
EP04004207A 2004-02-25 2004-02-25 Lautsprecher mit Bewegungsrückkopplung Withdrawn EP1569497A1 (de)

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007110252A1 (de) * 2006-01-20 2007-10-04 Anocsys Ag Verfahren zur bestimmung der position eines beweglichen teils eines elektroakustischen wandlers
WO2008125141A1 (de) * 2007-04-13 2008-10-23 Anocsys Ag Vorrichtung mit einem elektro-akustischen wandler
US20150086027A1 (en) * 2012-03-23 2015-03-26 Audi Ag Method for operating a loudspeaker device, loudspeaker device, and device for noise compensation
US20160302018A1 (en) * 2015-04-09 2016-10-13 Audera Acoustics Inc. Acoustic transducer systems with position sensing
US10516957B2 (en) 2014-11-28 2019-12-24 Audera Acoustics Inc. High displacement acoustic transducer systems
US20210021918A1 (en) * 2018-09-06 2021-01-21 Goertek Inc. Method for displacement measurement in a driver and speaker

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS55138998A (en) * 1979-04-16 1980-10-30 Matsushita Electric Ind Co Ltd Speaker
JPS55153495A (en) * 1979-05-17 1980-11-29 Sony Corp Motional feedback speaker
EP0048116A1 (de) * 1980-09-04 1982-03-24 The Rank Organisation Limited Lautsprecher mit Schwingspule
US4606642A (en) * 1983-07-16 1986-08-19 Dr. Johannes Heidenhain Gmbh Measuring arrangement for the clear scanning of at least one reference mark allocated to a graduation
JPH06284492A (ja) * 1993-03-30 1994-10-07 Kenwood Corp スピーカの振動検出装置
US5418362A (en) * 1993-05-27 1995-05-23 Lusby; Brett L. Encoder for determining absolute linear and rotational positions
US6445456B2 (en) * 1996-12-17 2002-09-03 Dr. Johannas Heidenhain Gmbh Photoelectric position measuring device
US20030111537A1 (en) * 2001-12-19 2003-06-19 Kai-Yuan Tien Light source mechanism of barcode scanner

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS55138998A (en) * 1979-04-16 1980-10-30 Matsushita Electric Ind Co Ltd Speaker
JPS55153495A (en) * 1979-05-17 1980-11-29 Sony Corp Motional feedback speaker
EP0048116A1 (de) * 1980-09-04 1982-03-24 The Rank Organisation Limited Lautsprecher mit Schwingspule
US4606642A (en) * 1983-07-16 1986-08-19 Dr. Johannes Heidenhain Gmbh Measuring arrangement for the clear scanning of at least one reference mark allocated to a graduation
JPH06284492A (ja) * 1993-03-30 1994-10-07 Kenwood Corp スピーカの振動検出装置
US5418362A (en) * 1993-05-27 1995-05-23 Lusby; Brett L. Encoder for determining absolute linear and rotational positions
US6445456B2 (en) * 1996-12-17 2002-09-03 Dr. Johannas Heidenhain Gmbh Photoelectric position measuring device
US20030111537A1 (en) * 2001-12-19 2003-06-19 Kai-Yuan Tien Light source mechanism of barcode scanner

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 005, no. 011 (E - 042) 23 January 1981 (1981-01-23) *
PATENT ABSTRACTS OF JAPAN vol. 0050, no. 27 (E - 046) 18 February 1981 (1981-02-18) *
PATENT ABSTRACTS OF JAPAN vol. 1995, no. 01 28 February 1995 (1995-02-28) *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007110252A1 (de) * 2006-01-20 2007-10-04 Anocsys Ag Verfahren zur bestimmung der position eines beweglichen teils eines elektroakustischen wandlers
WO2008125141A1 (de) * 2007-04-13 2008-10-23 Anocsys Ag Vorrichtung mit einem elektro-akustischen wandler
US20150086027A1 (en) * 2012-03-23 2015-03-26 Audi Ag Method for operating a loudspeaker device, loudspeaker device, and device for noise compensation
US10516957B2 (en) 2014-11-28 2019-12-24 Audera Acoustics Inc. High displacement acoustic transducer systems
US20160302018A1 (en) * 2015-04-09 2016-10-13 Audera Acoustics Inc. Acoustic transducer systems with position sensing
US10034109B2 (en) * 2015-04-09 2018-07-24 Audera Acoustics Inc. Acoustic transducer systems with position sensing
US20180376269A1 (en) * 2015-04-09 2018-12-27 Audera Acoustics Inc. Acoustic transducer systems with position sensing
US20210021918A1 (en) * 2018-09-06 2021-01-21 Goertek Inc. Method for displacement measurement in a driver and speaker

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