Speaker

Abstract: A speaker having a voice coil bobbin wound around with the voice coil and a detection coil together. The detection coil is formed by a wire whose diameter is smaller than one fourth of that of the wire used for the voice coil, and wound in a space among the voice coil wires. In other example, the voice coil and the detection coil are formed using a flat type wire. In a speaker made in accordance with the present invention, outer diameter of the whole coil structure containing a voice coil and a detection coil does not increase; as a result, decrement of the magnetic flux density in magnetic gap does not occur. Thus, the signals that proportionately represent the speaker vibration are made available without inviting deterioration in the efficiency of a speaker, nor an increased Q 0 .

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speaker having a function for delivering a signal that is proportionate to vibration of the diaphragm. 2. Description of the Prior Art In order to see the state of a vibrating speaker diaphragm, it is sometime necessary to pick up a signal that is proportionate to vibration of the diaphragm. A conventional speaker provided with a detection coil wound around voice coil bobbin for obtaining such proportionate signal is illustrated in FIG. 8, or disclosed in JP 09 289 699 A. Magnetic circuit 5 of the speaker is formed of a ring-shape magnet 3 disposed on a plate 2 having a center pole 1, and an upper plate 4. A frame 11 is connected on the magnetic circuit 5, and a cone-shape diaphragm 13 is adhered to the peripheral part of the frame 11 via an edge 12. A voice coil bobbin 9 wound around with a voice coil 7 and a detection coil 8 is connected to the diaphragm 13 at the center, the bobbin at its middle part is connected also to the frame 11 via a damper 10. The diaphragm 13 is attached in the center with a dust cap 14. Terminals 16, 18 provided on the frame 11 are attached respectively with flexible wires 15, 17; the respective other ends of the flexible wires 15, 17 are connected to the voice coil 7 and the detection coil 8 at a place in the middle of the voice coil bobbin 9. When an electric signal is applied to the terminal 16, the voice coil 7 disposed in a gap 6 of the magnetic circuit 5 moves in accordance with Fleming's left-hand rule to vibrate the diaphragm 13, which is connected with the voice coil bobbin 9. As a result, the diaphragm 13 generates a sound. As a result, in accordance with Fleming's right-hand rule, an electric signal is induced in the detection coil 8 in proportion to the motion of voice coil 7. The electric signal is delivered outside through the terminal 18. In the conventional speaker of the above configuration, which has a detection coil 8 wound around voice coil bobbin 9 for delivering the proportionate signals out , both the detection coil 8 and the voice coil 7 are formed with a same diameter wire having round cross section in two winding layers respectively, as illustrated in FIG. 9. This structure makes outer diameter of the whole coil structure greater, which eventually requires making the gap 6 proportionately wider. This causes problems; namely, the magnetic flux density in the magnetic gap 6 decreases, efficiency of the speaker deteriorates, furthermore, the Q 0 (sharpness of resonance) increases. SUMMARY OF THE INVENTION The present invention addresses the above problems. A speaker of the present invention, as claimed, forms a detection coil with a wire thinner than one fourth the diameter of that of voice coil wound around by making use of a space existing among the coiled wire of the voice coil. Other speaker of the present invention forms both the voice coil and the detection coil with a flat type wire, for obtaining the same sound output and the same detection capability as the conventional without inviting an increased overall dimensions of the whole coil structure. In accordance with the structure of the present invention, the outer diameter of a coil containing a voice coil and a detection coil does not increase, the density of magnetic flux in the magnetic gap does not decrease. Thus a signal that proportionately represents the vibration of diaphragm is made available without inviting deteriorated speaker efficiency and an increased Q 0 . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view of a speaker in accordance with a first embodiment of the present invention. FIG. 2 is a magnified cross sectional view of the voice coil portion in the first embodiment. FIG. 3 is a cross sectional view showing details of the voice coil portion of a comparative example which is not claimed. FIG. 4 is a cross sectional view of a voice coil wire in the comparative example. FIG. 5 is a cross sectional view showing details of the voice coil portion in a second embodiment. FIG. 6 is a cross sectional view showing details of the voice coil portion of a comparative example which is not claimed. FIG. 7 is a cross sectional view showing details of the voice coil portion of a comparative example which is not claimed. FIG. 8 is a cross sectional view showing the structure of a conventional speaker. FIG. 9 is a magnified cross sectional view of the voice coil portion of a conventional speaker. DETAILED DESCRIPTION OF THE INVENTION Speakers in accordance with exemplary embodiments of the present invention and comparative examples are described in the following with reference to the drawings. First embodiment FIG. 1 shows a cross sectional view of a speaker in a first exemplary embodiment of the present invention. Magnetic circuit 25 in the present embodiment is formed of a plate 22 having a center pole 21, a ring-shape magnet 23, and a ring-shape upper plate 24 disposed on the magnet 23. These are connected together with an adhesive. On the top of the upper plate 24, a frame 31 is connected by welding or by adhering, and the frame 31 is connected at the circumference to an edge 32. The edge 32 is made of a flexible and elastic material, and is connected with the peripheral part of a diaphragm 33. A voice coil bobbin 29 is connected with the diaphragm 33 at the center, which voice coil bobbin 29 is wound around at the lower part with a voice coil 27 and a detection coil 28. The voice coil bobbin 29 is held in a magnetic gap 26 of the magnetic circuit 25 without an eccentricity, and supported at the middle part by a damper 30. The damper 30 is connected at the circumference to the frame 31. The voice coil bobbin 29 disposed at the center of the diaphragm 33 is capped at the top with a dust cap 34. The voice coil 27 is connected to a terminal 36 with flexible wires 35, while the detection coil 28 is connected to a terminal 38 with flexible wires 37. Operation of the speaker is described next. Electric signal applied to the terminal 36 are delivered to the voice coil 27 via the flexible wires 35. The voice coil bobbin 29 makes a piston motion driven in accordance with Fleming's left-hand rule by the magnetic flux in the magnetic gap 26 and the electric current flowing in the voice coil 27. The piston motion moves the diaphragm 33, and the diaphragm outputs sound in accordance with the electric signal. Now, in accordance with Fleming's right-hand rule, an electromotive force is induced in the detection coil 28. The electromotive force flows through the flexible wire 37 to be picked up from the terminal 38. The driving force F (unit : N) generated in voice coil 27 by the electric signal delivered to the voice coil 27 is represented by equation 1 below. Where; "I" is electric current in the voice coil 27 (unit : A), "l" is length of the voice coil 27 disposed in the magnetic gap 26, "B" is density of magnetic flux in the magnetic gap 26 (unit: Web/m 2 ). The electromotive force E (unit : V) induced in the detection coil 28 by the motion of the voice coil bobbin 29 is represented by equation 2 below. Where; "V" is velocity of the motion of voice coil bobbin 29 (unit : m/s). Either of the driving force F and the electromotive force E are in proportion to the magnetic flux density in the magnetic gap 26. The Q 0 of a speaker is inversely proportionate to the square of the magnetic flux density in the magnetic gap 26. F = B l I E = B l V The detection coil 28 in a speaker of the present embodiment is formed by a wire whose diameter is less than one fourth of that of the wire of voice coil 27, and is wound by making use of a space existing among the coiled wire of the voice coil 27. With the above structure, outer diameter of the whole coil structure formed of the voice coil 27 and the detection coil 28 remains the same as that without having the detection coil 28. Therefore, in designing a speaker, there is no need of expanding the magnetic gap 26; hence, there is no decrease in the density of magnetic flux in the magnetic gap 26. As described in the above, a speaker in the present embodiment enables to pick up electric signals that are in proportion to the vibration of diaphragm, without inviting deteriorated speaker efficiency, nor an increased Q 0 . Thus the state of diaphragm vibration can be precisely detected without causing deterioration in the speaker efficiency. Comparative example A speaker of a comparative example which is not claimed is described with reference to FIG. 3 and FIG. 4. A speaker in the present example differs from that of the first embodiment in the following three points: (1) A flat type wire is used for the voice coil 27, in place of the round wire used in embodiment 1. Cross sectional shape of the flat type wire is a rectangle having the same area as that of a round wire whose cross sectional area is complying in calculation with the electric current of the speaker, and the width of the flat type wire being the same as diameter of the round wire as shown in Fig. 4. (2) A detection coil 28 is formed with a flat type wire. Thickness of the flat type wire is equivalent to a value obtained by subtracting the length of shorter side of the flat type wire from a diameter of the round wire of the voice coil 27. (3) First, a detection coil 28 is formed by winding the flat type wire around the voice coil bobbin 29 in a manner that the direction of thickness of the flat type wire (direction of shorter side of the cross sectional rectangle) is perpendicular to the outer surface of voice coil bobbin 29. Next, a voice coil 27 is formed on the outer surface of the detection coil 28 by winding the flat type wire so that the direction of thickness of the flat type wire is perpendicular to the outer surface of the voice coil bobbin 29. Second embodiment A speaker in a second exemplary embodiment is described with reference to FIG. 5. A speaker in the second embodiment uses the same flat type wire as that in the comparative example. The flat type wire is wound around with the thickness direction of wire in parallel with the outer surface of the voice coil bobbin 29 as shown in Fig. 5. Respective wires of voice coil 27 and detection coil 28 are wound stacking one after another in the axial direction of voice coil bobbin 29. The above described structure provides the same effect as that in the first embodiment. Furthermore, since the flat type wire is wound around in the direction of the wider width, mechanical strength of the voice coil 27 is enhanced to increase a reliability of the voice coil 27. Comparative example A speaker in a further comparative example, which is not claimed, is described with reference to FIG. 6. A voice coil bobbin 29 of a speaker in the further comparative example is formed of a metal foil tape 39 for reinforcement wound spirally with a gap, which metal foil tape 39 is adhered and sandwiched with insulating sheets 40, made of paper or resin, on both surfaces. Signals generated in proportion to the motion of voice coil bobbin can be taken out from both ends of the metal foil tape 39. Namely, a spirally-wound tape 39 of metal foil is used for the detection coil 28 in the present embodiment. The above described structure provides the effect that the mechanical strength of the voice coil bobbin 29 can be enhanced. Furthermore, since a speaker in the present example does not require any modification in the manufacturing process steps of conventional speakers, a possible increase in the manufacturing cost which could be incurred with the present speaker may be suppressed. Comparative example A speaker in a further comparative example, which is not claimed, is described with reference to FIG. 7. A speaker in the comparative example differs from that in the previous comparative example in that a flexible printed circuit board having an insulating layer on both surfaces rounded into a cylindrical form is used for the voice coil bobbin 29 in the present speaker. The flexible printed circuit board is shaped into a cylindrical form so that a conductive foil contained therein constitute a spiral along the axial direction of the cylinder. Signals generated in proportion to the motion of voice coil bobbin 29 are taken out from both ends of the conductive foil. The above described structure provides the same effect as that in the previous comparative example, and the structure controls a possible increase in the weight of the vibrating parts of a speaker to the smallest. As described in the above, a speaker of the present invention enables to deliver electric signals that are in proportion with the vibration of diaphragm, without inviting such drawbacks as a deteriorated speaker efficiency or an increased Q 0 .

Claims: A speaker comprising a voice coil (27) and a detection coil (28) each being formed of a wire having a round cross-section and wound together around a voice coil bobbin (29), characterised in that said detection coil(28) is formed with a wire having a diameter of less than one fourth of a diameter of said voice coil wire, the voice coil (27) is wound around the bobbin (29) thus forming voice coil wire windings such that there is a space formed between the voice coil wire windings, and the wire of said detection coil (28) is wound around the voice coil bobbin (29) in the space of the voice coil wire windings and among the voice coil wire windings. A speaker comprising a voice coil (27) and a detection coil (28) each being formed of a flat type wire having a rectangular cross-section and wound together around a voice coil bobbin (29), characterised in that said voice coil (27) is wound with the shorter side of the cross sectional rectanglein parallel with the outer surface of said voice coil bobbin (29), and respective wires of said voice coil (27) and said detection coil(28) are wound alternately one after the other in the axial direction on said voice coil bobbin (29).

Inventors: HASEGAWA AKINORI, KONNO FUMIYASU, ONISHI MASAHIDE, HASEGAWA,AKINORI, KONNO, FUMIYASU, ONISHI, MASAHIDE
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 2000
Main classification: H04R9
IPC codes: H04R9