Abstract:
A frame is provided with an opening allowing insertion of a jig for setting an inner rim of a suspension holder to a proper position. The jig ensures positive alignment of the suspension holder when making connection to the frame. The jig also ensures reliable bonding of a diaphragm to the suspension holder with a bonding agent, since it steadily supports the suspension holder in position during the bonding process. The positioning of the bobbin and a voice coil is thus reliable when being assembled, thereby improving acoustic performance of a speaker.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a speaker having a suspension holder, and a method of manufacturing the same.  
         [0003]     2. Background Art  
         [0004]      FIG. 17  is a sectional view of a conventional speaker. This speaker has magnetic circuit  55 , bobbin  58 , diaphragm  59 , frame  62  and suspension holder  63 . Magnetic circuit  55  is constructed of annular magnet  51 , annular plate  52 , discoid yoke  53  and cylindrical pole  54 . Bobbin  58  has voice coil  57  placed inside magnetic gap  56 . An inner perimeter of diaphragm  59  is connected to an outer periphery of bobbin  58 . An outer perimeter of diaphragm  59  is connected to frame  62  through first surround  60 . Suspension holder  63  supports diaphragm  59  and is connected to frame  62  through second surround  61 .  
         [0005]     This structure can substantially reduce a weight of suspension holder  63 . That is, an overall area of suspension holder  63  can be decreased because it is connected to diaphragm  59 , instead of it being connected directly to bobbin  58 . As a result, the weight of suspension holder  63  is substantially lightened. A speaker of such kind is disclosed in Japanese Patent Unexamined Publication, No. 2004-7331,for example.  
         [0006]     In the conventional structure described above, however, the presence of diaphragm  59  obstructs a worker from observing an area where diaphragm  59  and suspension holder  63  are bonded with adhesive when assembling the speaker. This gives rise to a possibility of causing misalignment of a certain extent in position of voice coil  58  in relation to diaphragm  59 . If there is a positional misalignment of bobbin  58  connected to diaphragm  59  or voice coil  57  disposed to bobbin  58  as stated above, it results in degradation of acoustic characteristic of the speaker.  
       SUMMARY OF THE INVENTION  
       [0007]     A speaker of the present invention has a magnetic circuit having a magnetic gap, a bobbin, a diaphragm, a frame, a suspension holder, a bonding agent, a first surround and a second surround. The bobbin has a voice coil disposed inside the magnetic gap. An inner perimeter of the diaphragm is bonded to an outer periphery of the bobbin. An outer perimeter of the diaphragm is connected to the frame via the first surround. The suspension holder supports the diaphragm on its inner rim, and an outer rim is connected to the frame via the second surround. The bonding agent bonds the inner rim of the suspension holder to the diaphragm. The frame has an opening in a position corresponding to an area of the bonding agent. In this structure, the opening provided in the frame allows insertion of a jig for guiding the inner rim of the suspension holder to a proper position. As a result, the suspension holder is properly aligned when it is connected to the frame, and the suspension holder thus stays steady when the diaphragm is fixed to it with the bonding agent. This ensures accurate positioning of the bobbin and the voice coil when being fixed, so as to prevent degradation of the acoustic characteristic of the speaker. In addition, since this structure brings a phase of the diaphragm into substantially equal to that of the suspension holder, it can reduce resonance distortion in the mid- to low-frequency ranges, which is attributable to a difference between their phases, and flatten the frequency characteristic. Accordingly, the present invention can improve the acoustic characteristic of the speaker. In addition, this invention discloses a method of manufacturing the speaker using the jig inserted through the opening as discussed above. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a sectional view of a speaker according to a first exemplary embodiment of the present invention.  
         [0009]      FIG. 2  is an enlarged sectional view of the speaker shown in  FIG. 1 , depicting a portion where a diaphragm and a suspension holder are bonded.  
         [0010]      FIG. 3  is a rear view of the speaker shown in  FIG. 1 .  
         [0011]      FIG. 4  is a graph representing a characteristic of power linearity of the speaker shown in  FIG. 1 .  
         [0012]      FIG. 5  is a graph representing characteristics of output sound pressure and harmonic distortion of the speaker shown in  FIG. 1 .  
         [0013]      FIG. 6  is a sectional view of the speaker showing a method of manufacturing the same according to the first exemplary embodiment of this invention.  
         [0014]      FIG. 7A  is a perspective view of a jig shown in  FIG. 6 .  
         [0015]      FIG. 7B  is an enlarged view of a protruding portion of the jig shown in  FIG. 6 .  
         [0016]      FIG. 8  is a sectional view of a speaker according to a second exemplary embodiment of the present invention.  
         [0017]      FIG. 9  is an exploded side view of a speaker according to a third exemplary embodiment of the present invention.  
         [0018]      FIG. 10  is a side view of a speaker according to a fourth exemplary embodiment of the present invention.  
         [0019]      FIG. 11  is a sectional view of a speaker according to a fifth exemplary embodiment of the present invention.  
         [0020]      FIG. 12  is an enlarged sectional view of a portion of a speaker where a second surround and a suspension holder are bonded, according to a sixth exemplary embodiment of the present invention.  
         [0021]      FIG. 13  is an enlarged sectional view of a portion of a speaker where a second surround and a suspension holder are bonded, according to a seventh exemplary embodiment of the present invention.  
         [0022]      FIG. 14  is an enlarged sectional view of a portion of a speaker where a second surround and a suspension holder are bonded, according to an eighth exemplary embodiment of the present invention.  
         [0023]      FIG. 15  is an enlarged sectional view of a portion of a speaker where a diaphragm and a suspension holder are bonded, according to a ninth exemplary embodiment of the present invention.  
         [0024]      FIG. 16  is a sectional view of a speaker according to a tenth exemplary embodiment of the present invention.  
         [0025]      FIG. 17  is a sectional view of a conventional speaker. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     Description is provided hereinafter of exemplary embodiments of the present invention with reference to the accompanying drawings. In each of the exemplary embodiments, same reference numerals are used throughout to designate components of like structures and like functions as those of the preceding exemplary embodiment(s), and detailed description of them will be omitted.  
       FIRST EXEMPLARY EMBODIMENT  
       [0027]      FIG. 1  is a sectional view of a speaker according to the first exemplary embodiment of this invention.  FIG. 2  is an enlarged sectional view of the speaker shown in  FIG. 1 , depicting a portion and the vicinity where diaphragm  9  and suspension holder  13  are bonded. The speaker of this exemplary embodiment has magnetic circuit  5 , bobbin  8 , diaphragm  9 , frame  12 , suspension holder  13  and bonding agent  14 . Magnetic circuit  5  has discoid magnet  1 , discoid plate  2 , discoid yoke  3  and cylindrical pole  4 . Bobbin  8  is provided on its inner periphery with voice coil  7  disposed in magnetic gap  6 . An inner perimeter of saucer-like diaphragm  9  is connected to an outer periphery of bobbin  8 . Cylindrical frame  12  having a closed bottom makes up an exterior enclosure of the speaker, retains magnetic circuit  5  therein, and is connected to an outer perimeter of diaphragm  9  through first surround  10 . Suspension holder  13  of generally a cylindrical shape having a smaller diameter at the upper side than the lower side is located inside frame  12 , and supports diaphragm  9  with its inner rim  13 A while its outer rim  13 B is connected to frame  12  through second surround  11 . Bonding agent  14  composed of adhesive or the like material secures inner rim  13 A of suspension holder  13  to diaphragm  9 . Besides, frame  12  has openings  15  in positions of the bottom area corresponding to bonding agent  14  for insertion of a jig.  
         [0028]     It is desirable that both first surround  10  and second surround  11  are substantially similar in shape and arranged symmetrically with respect to each other across a mid space between them. In this exemplary embodiment, first surround  10  is formed to bulge in a direction opposite magnetic circuit  5 , and second surround  11  is formed to bulge in a direction toward the bottom side of magnetic circuit  5 . In this case, it is desirable that both first surround  10  and second surround  11  are substantially equal in their modulus of elasticity.  
         [0029]     Inner rim  13 A (i.e., the upper side having a smaller diameter) of suspension holder  13  is bonded to bonding portion  16  on a lower surface at a mid area of diaphragm  9 . This can achieve a substantial reduction in weight of suspension holder  13  as compared to the conventional structure in which a suspension holder is bonded directly to a bobbin. Besides, bonding agent  14  is used to bond the two components. It is desirable that the bonding is made primarily in an area around outer boundary of inner rim  13 A of suspension holder  13  closer to the side of frame  12 . This arrangement prevents bonding agent  14 , normally of a fluid adhesive, from getting into magnetic gap  6  even if it drips down below. Furthermore, bonding portion  16  may be located even more close toward diaphragm  9  than that shown in  FIG. 2 . It is also desirable that bonding agent  14  is made of a silicone-base adhesive.  
         [0030]     Outer rim  13 B (i.e., the lower side having a larger diameter) of suspension holder  13  is connected to frame  12  through second surround  11  at the side corresponding to the bottom of yoke  3  rather than the side near plate  2 . There is dustproof net  18  placed between suspension holder  13  and magnetic circuit  5 .  FIG. 3  is a rear view of the speaker shown in  FIG. 1 . Openings  15  of frame  12  are covered with dustproof nets  18 .  
         [0031]      FIG. 4  is a graph representing a characteristic of power linearity of the speaker shown in  FIG. 1 . That is,  FIG. 4  shows vibrating amplitude of diaphragm  9  in response to input signal. Curve  31  indicates a characteristic of vibrating amplitude versus input signal of a polarity for driving diaphragm  9  toward the rear side of the speaker. Curve  32  indicates another characteristic of vibrating amplitude versus input signal of an opposite polarity for driving diaphragm  9  toward the front side of the speaker.  
         [0032]      FIG. 5  is a graph representing characteristics of output sound pressure and harmonic distortion of the speaker shown in  FIG. 1 . In  FIG. 5 , what is shown is the fact that the larger the dynamic range of output sound pressure and harmonic distortion, the smaller the harmonic distortion the speaker produces. Curve  33  indicates the characteristic of output sound pressure, curve  34  indicates the characteristic of second harmonic distortion, and curve  35  indicates the characteristic of third harmonic distortion.  
         [0033]     The speaker constructed as described above has the first through the seventh features described hereinafter.  
         [0034]     First, frame  12  is provided with openings  15 , which make possible to have jig  24  inserted therethrough to guide inner rim  13 A of suspension holder  13  into proper position (to be described later with reference to  FIG. 6 ). Therefore, suspension holders  13  can be aligned properly when it is connected to frame  12 . In addition, suspension holder  13  is kept steady while diaphragm  9  is being bonded to it securely with bonding agent  14 . This structure can thus ensure accurate positioning of bobbin  8  and voice coil  7  when fixed, so as to prevent degradation of acoustic characteristics of the speaker.  
         [0035]     In addition, since this structure brings a phase of diaphragm  9  into substantially same phase with suspension holder  13 , it can reduce a resonance distortion in the mid- to low-frequency ranges which is attributable to a difference between the phases of diaphragm  9  and suspension holder  13 , and flatten the frequency characteristic. As a result, it can further improve the acoustic characteristics of the speaker.  
         [0036]     Secondly, bonding agent  14  of the silicon-base adhesive used between diaphragm  9  and suspension holder  13  can accurately secure suspension holder  13  to diaphragm  9 , and avoid diaphragm  9  from shifting in position. In other words, this method of bonding positively prevents bobbin  8  connected to diaphragm  9  and voice coil  7  attached to bobbin  8  from shifting in their positions, and thereby it improves the acoustic characteristics of the speaker.  
         [0037]     Both diaphragm  9  and suspension holder  13  individually have dimensional variations resulted in the course of manufacturing. They may cause a gap between diaphragm  9  and suspension holder  13  at bonding portion. The use of bonding agent  14  can fill up this gap. Moreover, elasticity of bonding agent  14  prevents diaphragm  9  and suspension holder  13  from structural deformation, and thereby improves the acoustic characteristics of the speaker.  
         [0038]     It is desirable that bonding portion  16  is located near the outer peripheral side of diaphragm  9 . In this way, there improves rigidness of diaphragm  9  because the location of bonding portion  16  is close to a boundary of diaphragm  9  where the rigidity generally decreases.  
         [0039]     Thirdly, suspension holder  13  and second surround  11  in combination with first surround  10  compose a suspension between bobbin  8  and frame  12 . In other words, magnetic circuit  5  is composed of plate  2 , magnet  1  and yoke  3  laid up in this order from the side of diaphragm  9 , and outer rim  13 B of suspension holder  13  is connected through second surround  11  to frame  12  at a position closer to the bottom side of yoke  3  and farther than the plate  2  side of magnetic circuit  5 . This structure can prevent rolling motion of voice coil  7  when it is driven. For this reason, this structure does not require a damper, which is normally employed in the conventional suspension, and thereby it can eliminate the primary cause of nonlinearity and asymmetry.  
         [0040]     Fourthly, first surround  10  bulges in the direction opposite magnetic circuit  5 , and second surround  11  bulges toward the bottom side of magnetic circuit  5 . This structure thus cancels the asymmetry in shape between first surround  10  and second surround  11 . Therefore, the structure fundamentally solves problems associated with nonlinearity and asymmetry of the suspension as is evident from the curves  31  and  32  in  FIG. 4 . In addition, the structures of first surround  10  and second surround  11  can avoid them from coming in contact with each other in their vibrating motion even if they are physically located in close proximity to each other. They therefore provide an enough space for large amplitude of vibrations, which can increase the maximum level of sound pressure producible by the speaker.  
         [0041]     Fifthly, both first surround  10  and second surround  11  are made substantially equal in the modulus of elasticity. Therefore, second surround  11  accurately cancels the nonlinearity of first surround  10 . This greatly rectifies the asymmetry of the suspension, decreases harmonic distortion of the speaker attributable to it, and improves the power linearity.  
         [0042]     It is also desirable that diaphragm  9  is so made that the outer side from bonding portion  16  linking diaphragm  9  to suspension holder  13  has a lower density than that of the inner side. Since this keeps a good balance between rigidity and a mass of diaphragm  9  as a whole, it can reduce the weight while maintaining the rigidity. As a result, it obviates degradation in efficiency (i.e., decrease in sound pressure) of the speaker.  
         [0043]     Sixthly, dustproof net  18  provided between suspension holder  13  and magnetic circuit  5  keeps dust and the like from getting into magnetic gap  6 .  
         [0044]     Seventhly, the outer rim of suspension holder  13  is connected to frame  12  through second surround  11  at the side corresponding to the bottom of yoke  3  rather than the upper side of plate  2 . This structure improves the acoustic characteristics of the speaker. In other words, the structure can prevent rolling motion of voice coil  7  to the maximum extent possible when being driven since it can make use of a full dimension of the speaker to maintain a distance between fulcrums of first surround  10  and second surround  11 . A original point of moving bobbin  8  lies between the two fulcrums of bobbin  8 , of which one is a connecting point of first surround  10  to frame  12  and the other is a connecting point of second surround  11  to frame  12 . Since moving bobbin  8  and these fulcrums form a triangle, this structure can stably support the bobbin  8  when being driven.  
         [0045]     Because of the reasons described above, the speaker of this exemplary embodiment has a high degree of acoustic characteristics as shown in  FIG. 5 . This feature is apparent from the curve  33 . In addition, the speaker of this exemplary embodiment achieves reduction of harmonic distortion attributable to the nonlinearity and asymmetry of the suspension, as shown by the curves  34  and  35 .  
         [0046]     Description is provided next of materials used for the individual components of the speaker according to this exemplary embodiment.  
         [0047]     First surround  10  and second surround  11  can be made by using such materials as urethane, rubber, foamed rubber, cloth and the like. In this exemplary embodiment here, they are made of urethane formed into a ridge having a semispherical shape in cross section. Frame  12  is cylindrical in shape with a closed bottom, and uses any of machine-pressed steel plate, molded plastic resin, die-cast aluminum and the like. To produce bobbin  8 , any material is suitable such as paper, plastic resin, metallic material like aluminum and the like. Suspension holder  13  can be produced with any of pulp, plastic resin and metallic materials. It is also desirable to use a silicone-base adhesive for bonding agent  14 , as stated previously.  
         [0048]     The individual components produced with the materials described above provide the following features. While it is important for first surround  10  and second surround  11  not to impress an undue load on the moving motion of diaphragm  9 , use of urethane can improve efficiency of the speaker since this material can make elastic deformation and remove an extra weight from the vibration system. Alternatively, first surround  10  and second surround  11  may be made with common rubber or foam rubber. In this case, a level of compliancy of first surround  10  and second surround  11  can be controlled freely even if the speaker has no damper, so as to adjust the lowest resonance frequency “fo” to an optimum value.  
         [0049]     Frame  12  can be formed into any complex shape to meet the necessity by using the machine-pressed steel plate, molded plastic resin, die-cast aluminum and the like.  
         [0050]     Suspension holder  13  made of such material as pulp and plastic resin achieves both high rigidity and optimum level of internal loss. Use of a lightweight material as mentioned above can limit an increase in weight of the speaker even though it has first surround  10  and second surround  11 . As a result, this improves an efficiency of the speaker. Moreover, a metallic material of high thermal conductivity such as aluminum, when used for bobbin  8  and suspension holder  13 , efficiently dissipates heat generated by voice coil  7  through bobbin  8  and suspension holder  13 . It therefore increases the maximum permissible power input to the speaker.  
         [0051]     Although the speaker of this exemplary embodiment is illustrated as having magnetic circuit  5  of an inner magnet structure, it may be of an outer magnet structure.  
         [0052]     Referring now to  FIG. 6 ,  FIG. 7A  and  FIG. 7B , description is provided hereinafter of a method of manufacturing the speaker according to this exemplary embodiment.  FIG. 6  is a sectional view of the speaker representing the manufacturing method,  FIG. 7A  is a perspective view of a jig shown in  FIG. 6 , and  FIG. 7B  is an enlarged view of a protruding portion of the jig.  
         [0053]     In the method of manufacturing the speaker according to this exemplary embodiment, frame  12  is secured first to jig  24  by inserting jig  24  into openings  15  of frame  12 . An open area of each of openings  15  is larger than a sectional area of a head of each of protruding portions of jig  24  so as to facilitate insertion of jig  24 . This also prevents jig  24  from being damaged by burrs and the like around openings  15  when it is inserted through openings  15 , and thereby it improves productivity of the speaker. Next, while inner rim  13 A of suspension holder  13  is kept supported on jig  24 , outer rim  13 B of suspension holder  13  is fixed to frame  12  through second surround  11 . Magnetic circuit  5  is now inserted in the central space of frame  12 , and bobbin  8  is placed in a manner that voice coil  7  is situated inside magnetic gap  6 . Following the above process, bonding agent  14  is applied to an upper part of suspension holder  13  supported by jig  24 . Afterwards, diaphragm  9  is placed on suspension holder  13 , and diaphragm  9  is bonded to suspension holder  13  with bonding agent  14 . Each head  24 B of jig  24  has a shape analogous in cross section to a curved portion of inner rim  13 A of suspension holder  13 .  
         [0054]     Description is now given of a material of jig  24 . An exterior side of each head  24 B is formed of a resin material having adhesive repelling property such as polyacetal resin. Heads  24 B of jig  24  are formed of a material that is harder than frame  12 , such as metal.  
         [0055]     Bottom part  24 A of jig  24  is L-shaped, and is secured in position by peripheral wall  12 A of frame  12  covering the side of magnetic circuit  5  and back wall  12 B covering the bottom of magnetic circuit  5 .  
         [0056]     The speaker manufactured according to the above processes can achieve high acoustic characteristics.  
         [0057]     The first reason is that jig  24  can stabilize positioning of the individual components. In other words, openings  15  provided in frame  12  allow insertion of jig  24  for setting inner rim  13 A of suspension holder  13  to the predetermined position. As a result, suspension holder  13  can be aligned properly when it is connected to frame  12 . Suspension holder  13  is also kept steady when diaphragm  9  is bonded to it with bonding agent  14 . For the above reasons, positions of bobbin  8  and voice coil  7  fixed to diaphragm  9  are kept steady within magnetic gap  6 , which obviates degradation of the acoustic characteristics of the speaker.  
         [0058]     Furthermore, since this method makes diaphragm  9  and suspension holder  13  into substantially same phase with each other, it reduces a resonance distortion in the mid- to low-frequency ranges which is attributed to a difference in the phase between diaphragm  9  and suspension holder  13 . It thus flattens the frequency characteristic. As stated, the reliable positioning of the components attained by jig  24  provides the speaker with high acoustic characteristics.  
         [0059]     The second reason is the shape of the heads of jig  24  which ensures steadiness in the positioning. In other words, each head  24 B of jig  24  is formed into a ridge-like shape so as to fit the curved portion of inner rim  13 A of suspension holder  13 , and to locate precisely the bonding portion  16  where diaphragm  9  is bonded to suspension holder  13 . As a result, this improves the acoustic characteristics.  
         [0060]     The third reason is the shape of bottom part  24 A of jig  24  which ensures proper positioning of it with respect to the bottom surface of frame  12 . That is, bottom part  24 A of jig  24  is L-shaped, as shown in  FIG. 6 , and is secured in position by two sides, each abutting on peripheral wall  12 A and back wall  12 B of frame  12  covering the magnetic circuit  5 . Therefore, jig  24  and frame  12  fit securely with each other.  
         [0061]     Jig  24  has a shape to stay standing as shown in  FIG. 6  and  FIG. 7A . Therefore, jig  24  can be moved while securely holding frame  12 . In other words, frame  12  can be placed securely on fixed self-standing jig  24 , since jig  24  has catches  26  for holding frame  12 . Because of this structure, jig  24  can be moved from one workstation to another while keeping frame  12  held connected to jig  24  when they are transferred through different assembling processes, for instance. Accordingly, this movability in the process of assembly can improve productivity of the speaker of high acoustic characteristics.  
         [0062]     It is desirable that the exterior sides of heads  24 B of jig  24  are formed of polyacetal resin which is a resin material having adhesive repelling property. This material can prevent undesirable adhesion of a nearby component to jig  24  due to accidental contact with bonding agent  14  when bonding agent  14  is applied to bonding portion  16  of diaphragm  9  and suspension holder  13 . It is also desirable that heads  24 B of jig  24  are formed of a material that is harder than frame  12 . Such material also improves productivity of the speaker. That is, jig  24  is not likely to get damaged if it is made of a harder material than frame  12 , even after use in the manufacturing of a large number of speakers, and thereby this improves the productivity.  
         [0063]     Described next pertains to the shape of heads  24 B of jig  24 . It is desirable that jig  24  has catch  26  on each of protruding portions  25  as shown in  FIG. 7B . In  FIG. 6 , jig  24  is set first into openings  15  of frame  12 , and jig  24  is then turned toward a predetermined direction. Jig  24  is thus secured to frame  12  with catches  26  engaged to upper edges of openings  15 .  
         [0064]     Jig  24  and frame  12  are secured together by the engagement of catches  26  with openings  15  in the above manner. As a result, the speaker of this exemplary embodiment can be moved from one workstation to another while being secured to jig  24  when it is transferred through different assembling processes. It thus improves productivity of the speaker.  
         [0065]     It is desirable in view of the manufacturing that annular-shaped magnetic body  27  of substantially equal diameter as protruding portions  25  of jig  24  is placed on top of diaphragm  9 , as shown in  FIG. 6 , when diaphragm  9  is bonded to suspension holder  13 . Magnetic body  27  placed in this manner holds diaphragm  9  on suspension holder  13 . In other words, bonding between diaphragm  9  and suspension holder  13  can be made securely by bonding agent  14  since attractive force acting between magnetic body  27  and magnetic circuit  5  depresses diaphragm  9  against suspension holder  13  supported on jig  24 . Magnetic body  27  can thus improve the productivity.  
       SECOND EXEMPLARY EMBODIMENT  
       [0066]      FIG. 8  is a sectional view of a speaker according to the second exemplary embodiment of the present invention. Although the speaker of this exemplary embodiment is basically analogous to the speaker of the first exemplary embodiment, it differs from that of the first exemplary embodiment in respect of the directions to which first surround  10  and second surround  11  are formed to bulge. In the speaker of this exemplary embodiment, first surround  10  bulges in the direction toward the bottom side of magnetic circuit  5 , and second surround  11  bulges toward diaphragm  9 .  
         [0067]     In the above structure, first surround  10  does not become obstructive to mounting the speaker even if there is no spatial margin in front of first surround  10  (i.e., upper side of the speaker drawn in  FIG. 8 ). In an apparatus provided with a perforated net over and in close proximity of a sound opening where the speaker is mounted, for example, this structure can avoid first surround  10  from coming in contact with the perforated net even if the speaker is driven to a large amplitude of vibrations. This structure can thus increase the maximum sound pressure while achieving a low profile of the speaker.  
       THIRD EXEMPLARY EMBODIMENT  
       [0068]      FIG. 9  is an exploded side view of a speaker according to the third exemplary embodiment of this invention. The speaker of this exemplary embodiment differs from that of the first exemplary embodiment in respect that suspension holder  13  is provided with openings  28  in its wall between the inner rim and the outer rim. Other components are analogous to those of the first exemplary embodiment.  
         [0069]     These openings reduce an undesired sound output in the mid- to high-frequency ranges from suspension holder  13 , and prevent degradation of acoustic characteristics of the speaker due to interference of the sound output of suspension holder  13  with sound of diaphragm  9 . They can therefore improve the acoustic characteristics of the speaker.  
       FOURTH EXEMPLARY EMBODIMENT  
       [0070]      FIG. 10  is a side view of a speaker according to the fourth exemplary embodiment of this invention. The speaker of this exemplary embodiment differs from that of the first exemplary embodiment in respect that frame  12  is provided with openings  29  in its sidewall facing a wall between the inner and outer rims of suspension holder  13 . Other components are analogous to those of the first exemplary embodiment.  
         [0071]     These openings break confinement of an inner chamber formed by diaphragm  9 , first surround  10 , second surround  11 , frame  12  and suspension holder  13 . This inner chamber, if closed, causes sound output of suspension holder  13  to interfere with the sound of diaphragm  9 , and degrades the acoustic characteristics of the speaker. The openings prevent the interference and thereby improve the acoustic characteristics of the speaker.  
       FIFTH EXEMPLARY EMBODIMENT  
       [0072]      FIG. 11  is a sectional view of a speaker according to the fifth exemplary embodiment of this invention. The speaker of this exemplary embodiment differs from that of the first exemplary embodiment in respect that a wall between the inner and outer rims of suspension holder  13  is outwardly curved. Other components are analogous to those of the first exemplary embodiment. Arrows in  FIG. 11  indicate directions outward of suspension holder  13 .  
         [0073]     This structure improves rigidness of suspension holder  13  since the outwardly curved wall disperses the stress that tends to act upon suspension holder  13  in the outward direction. Consequentially, this structure improves the acoustic characteristics of the speaker. As an alternate structure, the wall between the inner and outer rims of suspension holder  13  may be curved inwardly to achieve the like advantageous effect.  
       SIXTH EXEMPLARY EMBODIMENT  
       [0074]      FIG. 12  is an enlarged sectional view of a portion of a speaker where second surround  11  and suspension holder  13  are connected according to the sixth exemplary embodiment of this invention. The speaker of this exemplary embodiment differs from that of the first exemplary embodiment in respect that outer rim  13 B of suspension holder  13  is bent into a shape of the letter L, and flat part  19  of this bottom end is connected in a face-to-face abutment to second surround  11 . Other components are analogous to those of the first exemplary embodiment.  
         [0075]     This structure increases rigidness of the connected portion, and improves the effect of dispersing a physical stress applied to the connected portion between suspension holder  13  and second surround  11 . This improves performance of the speaker to high input power and the acoustic characteristics of the speaker as a result.  
       SEVENTH EXEMPLARY EMBODIMENT  
       [0076]      FIG. 13  is an enlarged sectional view of a portion of a speaker where second surround  11  and suspension holder  13  are connected according to the seventh exemplary embodiment of this invention. The speaker of this seventh exemplary embodiment differs from that of the first exemplary embodiment in respect that outer rim  13 B of suspension holder  13  is bent into a shape of the letter L, and both faces of flat part  19  and angled adjoining part  20  are connected to second surround  11 . Other components are analogous to those of the first exemplary embodiment.  
         [0077]     This structure greatly increases the effect of dispersing the physical stress applied to the connected portion between suspension holder  13  and second surround  11 . This improves performance of the speaker to high input power, and thus the acoustic characteristics of the speaker.  
       EIGHTH EXEMPLARY EMBODIMENT  
       [0078]      FIG. 14  is an enlarged sectional view of a portion of a speaker where second surround  11  and suspension holder  13  are connected according to the eighth exemplary embodiment of this invention. The speaker of this exemplary embodiment differs from that of the first exemplary embodiment in respect that suspension holder  13  is connected to second surround  11  in a manner that outer rim  13 B is sandwiched between divided end flaps  21  of second surround  11 . Other components are analogous to those of the first exemplary embodiment.  
         [0079]     This structure also increases the effect of dispersing the physical stress applied to the connected portion between suspension holder  13  and second surround  11 , and improves performance of the speaker to high input power. As a result, it improves the acoustic characteristics of the speaker.  
       NINTH EXEMPLARY EMBODIMENT  
       [0080]      FIG. 15  is an enlarged sectional view of a portion of a speaker where diaphragm  9  and suspension holder  13  are bonded, according to the ninth exemplary embodiment of this invention. Although the speaker of this exemplary embodiment is basically analogous to that of the first exemplary embodiment, it differs in respect that outer side  9 A of diaphragm  9  is formed low in density than inner side  9 B. There is also a difference in respect that inner side  9 B of diaphragm  9  is formed flat. In addition, outer side  9 A of diaphragm.  9  is extended to form exterior rim  9 C which is connected to first surround  10 .  
         [0081]     According to this structure in which density of outer side  9 A from bonding portion  16  linking diaphragm  9  to suspension holder  13  is decreased as compared to density of inner side  9 B, diaphragm  9  can be lightened in weight without sacrificing the rigidness. The structure can thus improve the acoustic characteristics of the speaker.  
         [0082]     Moreover, inner side  9 B of diaphragm  9  is formed flat. This can reduce a front-to-back height of diaphragm  9 , thereby achieving low-profiling of the speaker.  
         [0083]     Furthermore, diaphragm  9  is provided with obtusely angled exterior rim  9 C throughout the perimeter of outer side  9 A, and inner edge  10 A of first surround  10  is also obtusely angled as shown in  FIG. 15 . Since these portions become substantially similar in shape to the connecting portion between suspension holder  13  and second surround  11 , they improve the acoustic characteristics of the speaker.  
       TENTH EXEMPLARY EMBODIMENT  
       [0084]      FIG. 16  is a sectional view of a speaker according to the tenth exemplary embodiment of this invention. The speaker of this tenth exemplary embodiment differs from that of the first exemplary embodiment in respect that it is provided with dust cap  23 . Other components are analogous to those of the first exemplary embodiment.  
         [0085]     Dust cap  23  is bonded to both bobbin  8  and diaphragm  9  with adhesive (not show in the figure) in a manner to cover the connected area between bobbin  8  and diaphragm  9 . Dust cap  23  is made primarily of pulp or plastic resin, and the adhesive used here is generally any of acrylic-base, silicone-base, rubber-base, and the like material.  
         [0086]     The above structure prevents dust and the like from getting into magnetic gap  6  within magnetic circuit  5 . It also increases a bonding strength between bobbin  8  and diaphragm  9 , which improves a dynamic balance of bobbin  8  in the moving directions toward the inside and the outside of magnetic circuit  5 . Since this structure accurately transmits a driving force of voice coil  7  to diaphragm  9 , it decreases a level of distortion and improves the acoustic characteristics of the speaker.  
         [0087]     As discussed above, the present invention can provide the speaker of high acoustic performance which is useful for a variety of acoustic apparatuses in all fields.