Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R29/00—Monitoring arrangements; Testing arrangements
  • H04R29/001—Monitoring arrangements; Testing arrangements for loudspeakers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
  • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
  • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
  • G01D5/241—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes
  • G01D5/2412—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes by varying overlap
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
  • H04R3/00—Circuits for transducers
  • H04R3/002—Damping circuit arrangements for transducers, e.g. motional feedback circuits

Definitions

• the present invention relates to a loudspeaker equipped with measurement of the movement of the loudspeaker unit, which loudspeaker includes
• the invention also relates to a method for measuring the movement of the loudspeaker unit in a loudspeaker.
• Typical dynamic loudspeakers have various drawbacks, which cause undesirable characteristics in the sound produced by the loudspeaker, such as harmonic distortion, uneven frequency response, and ringing. Attempts have been made to eliminate these problems by implementing various methods, which have been used to measure the sound produced by the loudspeaker in reality and to correct it to correspond as closely as possible to the desired sound.
• One way of measuring the sound produced by a loudspeaker is to measure the movement of the sound- producing unit (usually a cone) and to use the result obtained as a basis to correspondingly correct the control signal fed to the loudspeaker.
• the present invention is intended to create a new type of loudspeaker equipped with measurement of the movement of the loudspeaker unit, which has a simple construction and precise operation.
• the invention is intended to create a new type of method for measuring the movement of the loudspeaker unit in a loudspeaker, by means of which the problems appearing in previous measurement based on the change in capacitance can be avoided.
• the loudspeaker according to the invention is characterized by what is stated in the accompanying Claim 1.
• the method according to the invention is characterized by what is stated in the accompanying Claim 7.
• the capacitor is arranged in such a way that its capacitance is directly proportional to the deflection of the cone.
• the value of the capacitance is also bigger than in previously used loudspeakers.
• the said loudspeaker is created in such a way that the conducting surfaces of the capacitor are positioned parallel to the direction of movement of the loudspeaker unit and the value of the capacitor is altered either by changing the surface area between the plate-like conducting surfaces, or by moving the insulating material between the plate-like conducting surfaces.
• Other possible construction solutions for implementing the loudspeaker and method according to the invention are also itemized later.
• Figure 1 shows a cross-section of the loudspeaker according to the invention
• Figure 2 shows part of the circuit diagram of the loudspeaker according to the invention, for exploiting the measurement signal in the motional feedback of the loudspeaker.
• Figure 1 shows the loudspeaker unit according to the invention, which is constructed from a magnet 1, a front plate 2, a combined rear plate and centre piece 3, a component 4 arranged to vibrate, the component's outer suspension 5, the component's inner suspension ⁇ , a voice coil 7 moving in a magnetic field,
• a dynamic loudspeaker is created by fitting the loudspeaker unit according to the invention into a loudspeaker cabinet.
• the component arranged to vibrate is constructed from a cone and a dust cap.
• a cylindrical measurement capacitor is added to the centre of this loudspeaker.
• the conducting surface 9 of this capacitor connected to the constant voltage, in the case of the example 1200 V, is insulated by insulation
• the voice-coil cylinder 8 made of electrically conductive material, but is, however, mechanically connected to the movement of the cylinder.
• the voice-coil cylinder 8 is made from aluminium and is connected to a voltage of 0 V, i.e. to earth.
• the capacitor is formed of a cylindrical conducting surface 11, made from a conductive material and attached mechanically to the centre piece of the magnet, and which is electrically insulated from both the centre piece 3 of the magnet and the interference protection 12 connected to the constant voltage.
• the inner conducting surface 11 of the capacitor i.e. the cylinder, is connected to an operational amplifier 13, which, being equipped with suitable component values, produces a reference signal 14 proportional to the velocity of the cone 4.
• the usable frequency range of the measurement depends on the values of the feedback resistor and capacitor. In the case of the example, the value of the resistor is 1 M ⁇ and that of the capacitor 100 pF.
• a capacitor is also created between the cylinder 8 and centre piece of the voice coil, the capacitance of which changes on the basis of the movements of the cone 4. The change in this capacitor too can be used for measurement purposes. In the case of the example, however, this possibility is not used.
• the capacitor is generally connected to voltage with a magnitude of 500 - 5000 V. According to the invention, the mutual distance between the conducting surfaces of the capacitor remains the same, despite the movement of the loudspeaker unit. Even a high voltage can then be used, without the danger of punch-through or corona discharge.
• the reference signal obtained is typically exploited by using it to correct the non-ideal characteristics of the loudspeaker, for example, to eliminate distortion and to create the desired frequency response.
• a control signal 17 is produced for the loudspeaker with the aid of the sound signal 15 fed in and the correction circuit 16.
• the implementation of this correction circuit 16 depends a greatly on both the loudspeaker unit and the cabinet used.
• Figure 2 shows one possible example of a circuit.
• Figure 2 also shows the actual operational amplifier 13.
• the sound signal 15 fed in is first taken to an integrator-high-pass filter made around the operational amplifier 18, which alters the sound signal to correspond to the desired velocity of the loudspeaker unit.
• the circuit filters out frequencies of less than about 16 Hz, with a steepness of 12 dB/octave.
• the reference signal 14 depicting the velocity of the cone 4 is obtained from the operational amplifier 13, to the input of which the inner conducting surface 11 of the capacitor, i.e. in this case the cylinder, is connected.
• the outer conducting surface 9 is connected to a constant voltage, obtained from a voltage source 22.
• the signal 19 depicting the desired velocity and the reference signal 14 corresponding to the velocity of the measured unit are taken to a differential amplifier 20, which produces a signal 21 depicting the error in the velocity.
• the loudspeaker unit control signal 17 is obtained from this signal, either directly with the aid of a booster amplifier or by otherwise processing it. It may be necessary to process the control signal, for example, to eliminate vibration in the system caused by excessive phase shift in the feedback loop.
• a signal 21 directly depict- ing the error in the velocity is used as the control signal 17, however, after being taken through an amplifier stage with a current output sufficient to drive the loudspeaker unit.
• the value of the capacitance is also directly proportional to the deflection of the cone.
• the gap between the conducting surfaces of the capacitor may be quite small (in the order of millimetres) , in order for the change in the capacitance of the capacitor to be sufficiently great for the measurement to be sufficiently reliable and free of disturbance.
• the capacitor can be envisaged as being implemented in very many different ways.
• the capacitor need not have cylindrically shaped conducting surfaces, but can be implemented using, for example, a honeycomb or other similar shape, which will provide a greater capacitance per unit of length of the movement of the loudspeaker.
• the capacitor can also be implemented in such a way that the conducting surfaces of the actual capacitor remain stationary, but that the insulating material between them, which is connected to the movements of the cone, is moved. In this case it will be advantageous, in terms of obtaining a measurement result that is proportional to the deflection, that the amount of insulating material between the conducting surfaces will change in direct proportion to the deflection of the vibrating piece.
• the capacitor in terms of the method according to the invention, it will also be advantageous for the capacitor to be constructed in such a way that the normals of the conducting surfaces of the capacitor are sufficiently at right angles to the direction of movement of the vibrating piece, for the change in capacitance to be proportional to the deflection of the cone, to the required degree of accuracy.
• the capacitor can be used as part of an electronic vibration circuit, which has a natural frequency that is influenced by the capacitance of the capacitor, or else the impedance of the capacitor can be measured using the alternating voltage or current.
• a combination of the methods referred to above may also be considered, for example, if is wished to know the precise value of the deflection of the cone, for example, in order to limit the deviation of movement and at the same time the velocity or acceleration of the cone.
• the same method can also be used in other types of loudspeaker.
• the measurement results can also be used in very many different ways. For example, the measurement can be used to implement protection of the loudspeaker against excessive deflection values.

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Power Engineering (AREA)
• General Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Circuit For Audible Band Transducer (AREA)
• Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)

Applications Claiming Priority (3)

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• 2003
  • 2003-03-12 FI FI20030364A patent/FI118030B/fi active IP Right Grant
• 2004
  • 2004-03-11 EP EP04719481A patent/EP1606971A1/de not_active Withdrawn
  • 2004-03-11 WO PCT/FI2004/050027 patent/WO2004082330A1/en not_active Ceased

Non-Patent Citations (1)

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