Patent Publication Number: US-2019182602-A1

Title: Sound-producing device

Description:
CLAIM OF PRIORITY 
     This application is a Continuation of International Application No. PCT/JP2017/008268 filed on Mar. 2, 2017, which claims benefit of Japanese Patent Application No. 2016-159667 filed on Aug. 16, 2016. The entire contents of each application noted above are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sound-producing device that includes an armature extending through a coil and facing a magnet supported by a yoke and that produces a sound as vibrations of the armature are transmitted to a vibrator. 
     2. Description of the Related Art 
     Japanese Unexamined Patent Application Publication No. 2013-138292 discloses an invention related to a sound-producing device (electroacoustic transducer). 
     This sound-producing device includes a direct-current magnetic field generator. The direct-current magnetic field generator includes a first yoke, a second yoke, and a pair of permanent magnets supported by the respective yokes. An air core coil is disposed adjacent to the yokes, and the armature is disposed between the pair of opposing permanent magnets and inside the air core coil. 
     The armature is coupled to a vibrating plate by a rod. The armature vibrates in response to a current supplied to the coil, and these vibrations are transmitted to a vibrator, thus producing a sound. 
     The above publication discloses that the yokes are formed of PB permalloy (40-50% Ni—Fe). 
     PB permalloy (40-50% Ni—Fe) is used for the yokes supporting the permanent magnets of the sound-producing device (electroacoustic transducer) disclosed in the above publication. PB permalloy, which has a high magnetic saturation, i.e., 1.5 T or more, and good soft magnetic properties, is commonly used for various magnetic circuits. 
     However, it is not necessarily the best to select PB permalloy as a soft magnetic material for the yokes of a sound-producing device (electroacoustic transducer). 
     As described later with reference to  FIGS. 8A and 8B , the sound pressure level (SPL) of a sound-producing device including yokes formed of PB permalloy tends to show relatively large ripple noise at high frequencies of 2 kHz or more. It can be assumed that this is partly because an increased amount of heat is generated from the coil at high frequencies and increases the temperature of the yokes, which are adjacent to the coil in a narrow case. It is also assumed that ripple noise tends to occur at high frequencies when the ambient temperature increases. 
     As described later with reference to  FIG. 7 , PB permalloy has a linear expansion coefficient α of more than 10×10 −6 . Thus, as an increased amount of heat is generated from the coil and heats the yokes, the yoke size changes, which tends to vary the distance between the opposing magnets. 
     It is possible that this distance variation results in unnecessary vibrations of the armature. 
     It is also assumed that another cause is as follows. As an increased amount of heat is generated from the coil and changes the yoke size, the internal stress at the junctions between the magnets and the yokes and the junction between the yokes increases. As a result, when the magnetic flux generated from the magnets is transmitted to the armature, the flow regularity of the magnetic flux passing inside the yokes is degraded. 
     SUMMARY OF THE INVENTION 
     The present invention provides a sound-producing device that exhibits a stable sound pressure level at high frequencies. 
     A sound-producing device according to an aspect of the present invention includes, in a case, a yoke formed of a magnetic material, a magnet supported by the yoke, a coil, an armature extending through the coil and facing the magnet, and a vibrator configured to vibrate in response to operation of the armature. The yoke is formed of an Fe—Ni alloy containing 32% by mass to 40% by mass of Ni. 
     In the sound-producing device according to the above aspect, the Fe—Ni alloy preferably contains 36% by mass of Ni. 
     The sound-producing device according to the above aspect may be configured such that the magnet is secured to each of opposing inner surfaces of the yoke, the armature being located between the opposing magnets. 
     The sound-producing device according to the above aspect preferably has a frame disposed in the case, the vibrator being supported on one side of the frame, the yoke being secured to another side of the frame. 
     Furthermore, the case of the sound-producing device according to the above aspect is preferably composed of first and second cases combined together, the frame being held and secured between the first and second cases. 
     The yoke of the sound-producing device according to the above aspect is formed of an Fe—Ni alloy containing 32% by mass to 40% by mass of Ni. As shown in  FIG. 7 , Fe—Ni alloys containing Ni in amounts within this range have low linear expansion coefficients α. As shown in  FIGS. 8A and 8B , a sound-producing device including this yoke exhibits an improvement in terms of nipple noise at high frequencies. 
     According to the above aspect, even if an increased amount of heat is generated from the coil at high frequencies and increases the temperature of the yoke, which is housed in a narrow case, the change in yoke size can be reduced through the use of a yoke containing Ni in an amount within the above range. As a result, less variation occurs in the distance between the opposing magnets, and an increase in internal stress at the junctions between the yoke and the magnets and the junction between different parts of the yoke can be more easily prevented. The change in yoke size can also be reduced when the ambient temperature increases, and therefore, an increase in internal stress can be more easily prevented. 
     Thus, the sound pressure level at high frequencies of 2 kHz or more can be stabilized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the external appearance of a sound-producing device according to an embodiment of the present invention; 
         FIG. 2  is an exploded perspective view showing the sound-producing device according to the embodiment of the present invention; 
         FIG. 3  is a sectional view, taken along line III-III, of the sound-producing device shown in  FIG. 1 ; 
         FIG. 4  is a sectional view showing the sound-producing device shown in  FIG. 3  in a disassembled state; 
         FIG. 5  is a plan view of a frame of the sound-producing device according to the embodiment, with a vibrating plate, a first yoke, and an armature mounted thereon; 
         FIG. 6  is a sectional view, taken along line VI-VI, of the sound-producing device shown in  FIG. 3 ; 
         FIG. 7  is a graph showing the relationship between the Ni content and linear expansion coefficient of Fe—Ni alloys for forming yokes (source: PHYSICS &amp; APPLICATIONS OF PROPERTIES OF INVAR ALLOYS, P4 (Maruzen Publishing Co., Ltd.)); 
         FIG. 8A  is a characteristic graph showing the relationship between frequency and SPL for the Example; and 
         FIG. 8B  is a characteristic graph showing the relationship between frequency and SPL for the Comparative Example. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in, for example,  FIGS. 1 and 2 , a sound-producing device  1  according to an embodiment of the present invention includes a case  2 . The case  2  is composed of a first case  3  and a second case  4 . The first case  3  is a lower case, whereas the second case  4  is an upper case. Both cases  3  and  4  are formed from a nonmagnetic metal plate or a magnetic metal plate by press forming. 
     As shown in  FIG. 2 , the first case  3  has a bottom  3   a , a sidewall  3   b  enclosing the four sides thereof, and an opening edge  3   c  at the upper end of the sidewall  3   b . The second case  4  has a ceiling  4   a , a sidewall  4   b  enclosing the four sides thereof, and an opening edge  4   c  at the lower end of the sidewall  4   b . The first case  3  has a larger inner space than the second case  4 , which functions as a lid for the first case  3 . 
     As shown in  FIGS. 3 and 6 , a frame  5  is held between the opening edge  3   c  of the first case  3  and the opening edge  4   c  of the second case  4 . As shown in  FIG. 2 , the frame  5  is formed from a nonmagnetic or magnetic metal plate with uniform thickness in the Z direction. The frame  5  has an opening  5   c  formed through the center thereof from top to bottom. The opening  5   c  is a rectangular hole. 
     The frame  5  has a vibrator-mounting surface  5   b  around the opening  5   c  in the upper surface thereof as shown in the figures. The vibrator-mounting surface  5   b  is a frame-shaped flat surface. The frame  5  has a held portion  6  with reduced thickness that is integrally formed around the entire periphery of the vibrator-mounting surface  5   b . As shown in  FIGS. 3, 4, and 6 , the upper surface of the held portion  6  oriented in the same direction as the vibrator-mounting surface  5   b  is an upper joining contact surface  6   b . A step  7  is formed between the vibrator-mounting surface  5   b  and the upper joining contact surface  6   b.    
     This frame  5  is manufactured by press-forming a metal plate with uniform thickness. The opening  5   c  is formed by punching the metal plate. The held portion  6  is formed by pressing the periphery of the vibrator-mounting surface  5   b  so that its thickness in the Z direction is reduced. This pressing not only forms the held portion  6 , but also increases the rigidity of the frame  5 . 
     The lower surface, as shown in the figures, around the opening  5   c  in the frame  5  is a drive-mechanism mounting surface  5   a , and the surface of the held portion  6  facing downward as shown in the figures is a lower joining contact surface  6   a . The drive-mechanism mounting surface  5   a  and the lower joining contact surface  6   a  are the same flat surface. Alternatively, there may be a step between the drive-mechanism mounting surface  5   a  and the lower joining contact surface  6   a.    
     As shown in  FIGS. 3 and 4 , a vibrator  10  is mounted on the vibrator-mounting surface  5   b  of the frame  5 , which faces upward as shown in the figures. The vibrator  10  is composed of a vibrating plate  11  and a vibration support sheet  12 . The vibrating plate  11  is formed from a thin plate of a metal material such as aluminum or SUS304, optionally with a rib formed by press forming to enhance the bending strength. Although raised ribs are shown in  FIG. 6 , the ribs are omitted from  FIG. 2 . The vibration support sheet  12  is more flexible than the vibrating plate  11  and is formed from, for example, a sheet (film) of a resin such as polyethylene terephthalate (PET), nylon, or polyurethane. 
     The vibrating plate  11  and the vibration support sheet  12  are rectangular. The area of the vibrating plate  11  is smaller than the opening area of the opening  5   c  in the frame  5 , and the area of the vibration support sheet  12  is larger than the area of the vibrating plate  11 . As shown in  FIG. 6 , the vibrating plate  11  is secured to the lower surface of the vibration support sheet  12  by bonding with an adhesive. The outer periphery  12   a  of the vibration support sheet  12  is located outside the outer periphery of the vibrating plate  11 . This outer periphery  12   a  is secured to the frame-shaped upper surface of the frame  5 , i.e., the vibrator-mounting surface  5   b , with an adhesive therebetween. The bending and elasticity of the vibration support sheet  12  allow the vibrating plate  11  to vibrate while being fixed at a fixed end  11   c  thereof such that a free end  11   b  thereof is displaced in the Z direction. The fixed end  11   c  and the free end  11   b  are shown in  FIGS. 2, 3, and 4 . 
     As shown in  FIGS. 3 and 4 , a magnetic-field generating unit  20 , a coil  27 , and an armature  32  are mounted on the frame  5 . The magnetic-field generating unit  20  includes a first yoke  21  and a second yoke  22 . The soft magnetic material forming the first yoke  21  and the second yoke  22  is a Ni—Fe alloy containing 32% by mass to 40% by mass of Ni. 
     As shown in  FIG. 2 , the second yoke  22  is bent into a U-shape and has a bottom  22   a  and a pair of sides  22   b  and  22   b  bent upward on both sides in the X direction. The upper ends of the sides  22   b  and  22   b  are joined to the inner surface  21   a  of the first yoke  21 , which has a flat shape. The first yoke  21  and the second yoke  22  are secured together by a technique such as laser spot welding. When the first yoke  21  and the second yoke  22  are secured together, the inner surface of the bottom  22   a  of the second yoke  22  faces the inner surface  21   a  of the first yoke  21  so as to be parallel thereto. 
     As shown in  FIGS. 2, 4, and 6 , the magnetic-field generating unit  20  has a first magnet  24  secured to the inner surface  21   a  of the first yoke  21  and a second magnet  25  secured to the inner surface of the bottom  22   a  of the second yoke  22 . The magnets  24  and  25  are magnetized such that a magnetized surface  24   a  of the first magnet  24  is of opposite polarity to a magnetized surface  25   a  of the second magnet  25 . A gap δ is defined between the magnetized surface  24   a  of the first magnet  24  and the magnetized surface  25   a  of the second magnet  25  in the Z direction. 
     As shown in  FIGS. 2 and 3 , the coil  27  is disposed beside the magnetic-field generating unit  20 . The coil  27  is a covered conductor wound multiple turns about a winding axis extending in the Y direction. A winding end  27   a  of the coil  27  oriented in the Y direction is secured to the first yoke  21  and the second yoke  22  by bonding. Alternatively, a support plate formed of a nonmagnetic material may be secured to the downward-facing outer surface of the first yoke  21 , and the downward-facing outer winding portion of the coil  27  may be bonded to the support plate. 
     As shown in  FIGS. 2, 3, and 4 , the armature  32  is disposed in the sound-producing device  1 . The armature  32  is formed from a plate of a magnetic material with uniform thickness, for example, a Ni—Fe alloy. The armature  32  is press-formed into a U-shape having a movable portion  32   a , a base  32   b , and a bend  32   c . As shown in  FIG. 2 , a leading end  32   d  of the movable portion  32   a  of the armature  32  facing the free end side has a reduced width in the X direction and has a coupling hole  32   e  formed therethrough from top to bottom. 
     As shown in  FIGS. 3, 4, and 5 , the base  32   b  of the armature  32  is secured to an upward-facing outer surface  21   b  of the first yoke  21 . The movable portion  32   a  of the armature  32  is inserted into the winding space  27   c  of the coil  27  and is also inserted into the gap δ between the first magnet  24  and the second magnet  25 . The leading end  32   d  of the armature  32  protrudes out of the gap δ to the left as shown in the figures. 
     As shown in  FIGS. 3 and 4 , the upward-facing outer surface  21   b  of the first yoke  21  is joined and secured to the lower surface of the frame  5 , i.e., the drive-mechanism mounting surface  5   a . As shown in  FIGS. 5 and 6 , the first yoke  21  is disposed so as to cross the opening  5   c  in the frame  5  in the X direction, and both ends of the first yoke  21  in the X direction are joined to the drive-mechanism mounting surface  5   a  of the frame  5 . The first yoke  21  and the frame  5  are secured together by laser spot welding. By securing together the first yoke  21  and the frame  5 , the magnetic-field generating unit  20  is retained with respect to the drive-mechanism mounting surface  5   a  of the frame  5 . 
     As shown in  FIG. 5 , the base  32   b  of the armature  32  is smaller than the opening area of the opening  5   c  in the frame  5 . Thus, as shown in  FIG. 6 , when the outer surface  21   b  of the first yoke  21  is secured to the lower surface of the frame  5 , i.e., the drive-mechanism mounting surface  5   a , the base  32   b  of the armature  32 , which is secured to the outer surface  21   b , enters the opening  5   c  in the frame  5 . The thickness of the base  32   b  in the Z direction is smaller than the thickness of the frame  5  in the Z direction. Thus, a gap is formed between the vibrating plate  11 , which is also located in the opening  5   c , and the base  32   b  of the armature  32  in the Z direction so that the vibrating plate  11  can vibrate in the Z direction. 
     As shown in  FIG. 3 , the free end  11   b  of the vibrating plate  11  is coupled to the leading end  32   d  of the armature  32  by a transmitter  33 . The transmitter  33  is a needle-shaped member formed of a metal or a synthetic resin, for example, an SUS202 pin. An upper end  33   a  of the transmitter  33  is inserted into a mounting hole  11   e  formed in the vibrating plate  11 , and the vibrating plate  11  and the transmitter  33  are secured together with an adhesive or solder. A lower end  33   b  of the transmitter  33  is inserted into the coupling hole  32   e  formed in the leading end  32   d  of the armature  32 , and the transmitter  33  and the leading end  32   d  are secured together by laser spot welding or with an adhesive or solder. The transmitter  33  extends through the opening  5   c  in the frame  5  from top to bottom, and a portion of the transmitter  33  is located in the opening  5   c.    
     As shown in  FIGS. 3 and 6 , the held portion  6  integrally formed around the periphery of the frame  5  is held and secured between the opening edge  3   c  of the first case  3  and the opening edge  4   c  of the second case  4 . The opening edge  3   c  of the first case  3  abuts the lower surface of the held portion  6 , i.e., the lower joining contact surface  6   a , whereas the opening edge  4   c  of the second case  4  abuts the upper surface of the held portion  6 , i.e., the upper joining contact surface  6   b . The first case  3  and the second case  4  are secured to the held portion  6  by laser spot welding. Thus, the sound-producing device  1  shown in  FIG. 1  is finished. 
     The held portion  6  is integrally formed around the entire periphery of the frame  5 , and the step  7  is formed between the vibrator-mounting surface  5   b  and the upper surface of the held portion  6 , i.e., the upper joining contact surface  6   b . Thus, the junction between the upper joining contact surface  6   b  and the opening edge  4   c  of the second case  4  is discontinuous with the vibrator-mounting surface  5   b  at the step  7 . The presence of the step  7  prevents the adhesive for bonding the outer periphery  12   a  of the vibration support sheet  12  to the vibrator-mounting surface  5   b  from adhering to the junction between the upper joining contact surface  6   b  and the opening edge  4   c.    
     When the frame  5  is held and secured between the first case  3  and the second case  4 , the vibrating plate  11  and the vibration support sheet  12  divide the inner space of the case  2  into upper and lower spaces. The inner space of the second case  4  above the vibrating plate  11  and the vibration support sheet  12  is a sound-producing space. The sound-producing space leads to the outer space through a sound outlet opening  4   d  formed in the sidewall  4   b  of the second case  4 . 
     As shown in  FIG. 3 , a sound outlet nozzle  41  leading to the sound outlet opening  4   d  is secured outside the case  2 . As shown in  FIGS. 2 and 3 , an air inlet/outlet opening  3   d  is formed in the bottom of the first case  3 , and the inner space of the first case  3  below the vibrating plate  11  and the vibration support sheet  12  leads to the outside atmosphere through the air inlet/outlet opening  3   d . As shown in  FIG. 2 , a pair of wire holes  3   e  are formed in the sidewall  3   b  of the first case  3 . As shown in  FIG. 3 , a pair of terminal portions  27   b  of the conductor forming the coil  27  are routed outside through the wire holes  3   e . A substrate  42  is secured outside the sidewall  3   b  of the first case  3 , and the terminal portions  27   b  pass through small holes formed in the substrate  42 . By closing these small holes, the wire holes  3   e  are closed off from the outside. 
     The operation of the sound-producing device  1  will be described next. 
     When a voice current is supplied to the coil  27 , a magnetic field induced by the coil  27  and a magnetic field generated between the magnetized surface  24   a  of the first magnet  24  and the magnetized surface  25   a  of the second magnet  25  exert a vibrating force on the movable portion  32   a  of the armature  32  in the Z direction. These vibrations are transmitted through the transmitter  33  to the vibrating plate  11 . The vibrating plate  11 , which is supported by the vibration support sheet  12 , vibrates while being fixed at the fixed end  11   c  thereof such that the free end  11   b  thereof oscillates in the Z direction. These vibrations are transmitted to the vibrating plate  11 , thus producing a sound pressure in the inner sound-producing space of the second case  4 . This sound pressure is output from the sound outlet opening  4   d  to the outside. 
     The features of the sound-producing device  1  are as follows. 
     The first yoke  21  and the second yoke  22  of the sound-producing device  1  according to the embodiment are formed of an Fe—Ni alloy containing 32% by mass to 40% by mass of Ni. A feature of this Fe—Ni alloy is that it has a low linear expansion coefficient α. 
     “Fe—Ni alloy” as used herein refers to an alloy based on iron (Fe) and nickel (Ni). It should be understood that this term also encompasses alloys containing other minor constituents. Typically, in addition to Fe and Ni, about 0.7% by mass of manganese (Mn) and less than 0.2% by mass of carbon (C) are present as minor constituents. 
     As shown in  FIG. 7 , Fe—Ni alloys containing 32% by mass to 40% by mass of Ni have linear expansion coefficients α of 5×10 −6  or less, which are significantly lower than that of, for example, PB permalloy, which contains about 45% by mass of Ni. 
     As shown in  FIG. 3 , the sound-producing device  1  has the yokes  21  and  22  disposed adjacent to the coil  27  within the sealed narrow space of the case  2 . Thus, for example, when a drive current with a high frequency of 2 kHz or more is supplied to the coil  27 , the coil  27  generates an increased amount of heat, and this heat increases the temperature of the yokes  21  and  22  disposed adjacent thereto within the narrow space. 
     However, the yokes  21  and  22 , which are formed of the Fe—Ni alloy described above, have a low linear expansion coefficient and thus deform only slightly at elevated temperatures. Thus, the distance δ between the first magnet  24  and the second magnet  25  varies only a little at elevated temperatures, so that unnecessary vibrations and resonance of the armature  32  due to the variation in distance δ can be suppressed. Since the yokes  21  and  22  deform only slightly, stress concentration at the junctions between the magnets  24  and  25  and the yokes  21  and  22  and stress concentration at the junction between the first yoke  21  and the second yoke  22  can be alleviated. Thus, the flow regularity of the magnetic flux generated by the magnets  24  and  25  and flowing from the first yoke  21  to the armature  32  is not impaired, and as shown in  FIG. 8A , the ripple noise level R 1  of the sound pressure level at high frequencies of 2 kHz or more can be reduced. 
     Although the magnetic-field generating unit  20  in the embodiment is composed of the first yoke  21  and the U-shaped second yoke  22 , it is also possible to use a magnetic-field generating unit composed of a flat upper yoke, a flat lower yoke, and a pair of flat side yokes joined to the upper and lower yokes, that is, a total of four yokes. 
     EXAMPLES 
     (1) Example 
     A sound-producing device  1  serving as an Example included a first yoke  21  and a second yoke  22  that were formed of an Fe—Ni alloy containing 36% by mass of Ni. The plate thickness was 0.35 mm. A bulk of this alloy has a magnetic saturation of about 1.2 T. The width W 1  of the yokes  21  and  22  shown in  FIG. 2  in the Y direction was 1.6 mm, the width W 2  of the second yoke  22  in the X direction was 2.7 mm, and the height H of the magnetic-field generating unit  20  in the Z direction was 1.8 mm. 
     The first magnet  24  and the second magnet  25  were AlNiCo magnets. 
     The number of turns of the coil  27  was 200 turns. 
     The armature  32  was formed of PB permalloy, i.e., an Fe—Ni alloy containing 45% by mass of Ni, and had a plate thickness of 0.15 mm. 
     The vibrating plate  11  was formed of aluminum and had a plate thickness of 0.05 mm. 
     (2) Comparative Example 
     The first yoke  21  and the second yoke  22  were formed of PB permalloy, i.e., an Fe—Ni alloy containing 45% by mass of Ni. A bulk of PB permalloy has a magnetic saturation of about 1.5 T. The sizes of the first yoke  21  and the second yoke  22  and the structures of the magnetic-field generating unit  20  and the coil  27  were identical to those of the Example. 
     (3) Sound Pressure Level (SPL) Measurement 
     SPL was measured with a model 5265-2A sound analyzer (available from Etani Electronics Co., Ltd.). A coupler compliant to IEC 60318-4 was used. 
     The sound pressure level was measured with a power of 1 mW at 1 kHz (constant applied voltage) in the range from 10 Hz to 100 kHz. 
       FIG. 8A  shows the SPL measurement results for the Example, whereas  FIG. 8B  shows the SPL measurement results for the Comparative Example. Whereas the sound pressure levels in  FIGS. 8A and 8B  were similar over a wide range of frequencies of 2 kHz or more, the ripple noise level R 1  of the Example in  FIG. 8A  was nearly half the ripple noise level R 2  of the Comparative Example in  FIG. 8B .