Abstract:
A ribbon microphone unit includes: an electrode lead portion for conducting an electric signal which a ribbon diaphragm generates cooperating with a magnet; a tightening member for securing the ribbon diaphragm; and a screw for crimping the tightening member, wherein the tightening member is crimped via the ribbon diaphragm and the electrode lead portion by the screw, and wherein the ribbon diaphragm includes a portion sandwiched by the tightening member, and the portion is formed in an irregular shape in the thickness direction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to ribbon microphones and ribbon microphone units. 
     2. Related Background of the Invention 
     A ribbon microphone includes a magnet for forming a magnetic field and a ribbon diaphragm, as the main component members. The magnet is disposed on both sides of the ribbon diaphragm to sandwich the same, whereby a magnetic field is formed between the magnets on the both sides. The ribbon diaphragm is given an appropriate tension and disposed within the magnetic field while the both longitudinal ends are held down. In response to a sound wave, the ribbon diaphragm vibrates within the magnetic field and thereby a current corresponding to the sound wave flows through the ribbon diaphragm and thus the sound wave is converted into an electric signal. Typically, an aluminum foil is used as the material of the ribbon diaphragm. Since aluminium has a small conductive resistance as compared with other metallic materials and also has a low specific gravity, aluminium is suitable as the ribbon diaphragm of the ribbon microphone. 
     An electric signal which the ribbon diaphragm generates cooperating with the field is weak. Accordingly, the ribbon microphone commonly known includes a transformer to boost the voltage of a weak electric signal. However, since the electric signal flows, as a weak electric signal as is, on an electric circuit from the ribbon diaphragm to the transformer, the conductive resistance needs to be reduced as much as possible. If the conductive resistance is large, the sensibility of the electric signal will decrease and the expected acoustic characteristics cannot be obtained. 
       FIG. 5  shows an example of a typical ribbon microphone.  FIG. 6  shows an example of a ribbon microphone unit built in this ribbon microphone. In  FIG. 5 , in a ribbon microphone  1 , a housing of the microphone comprises a cylindrical base  6  and a microphone case  2  connected to the top end of the base  6 . Inside this housing, a ribbon microphone unit  3  is assembled to a suitable support member that is secured to the base  6 . The microphone unit  3  is covered with the microphone case  2 . The bottom end of the base  6  is a connector portion  16 , to which a microphone cable for delivering the output signal of the microphone to an external circuit is connected. 
     As also shown in  FIG. 6 , the ribbon microphone unit  3  includes a frame  7  formed in a rectangular frame shape that is long in the longitudinal direction. On both sides of the inner surface of the frame  7 , a pair of permanent magnets  4 ,  4  are fixed along the longitudinal direction, with a predetermined spacing between the both permanent magnets  4 ,  4 . The permanent magnets  4 ,  4  are magnetized in the width direction (horizontal direction in  FIG. 6 ), and the directions of the magnetization of the pair of permanent magnets  4 ,  4  are the same. Accordingly, the parallel field is formed between the permanent magnets  4 ,  4 . 
     Within the parallel field, a ribbon diaphragm (hereinafter, may be referred to simply as a “ribbon”)  5  combining a diaphragm with a conductor is disposed. As shown in  FIG. 10 , the ribbon  5  forms a long and slender band shape, and both longitudinal ends thereof are secured to electrode lead portions  18 ,  18  provided on both longitudinal ends of the frame  7 . The electrode lead portions  18 ,  18  are insulated from the frame  7 , and are conducted to the ribbon  5  by sandwiching both ends of the ribbon  5  using tightening members comprising pressure plates  8 ,  8  and support plates  81 ,  81 . Moreover, the electrode lead portions  18 ,  18  hold the ribbon  5  in a state where the ribbon  5  is given an appropriate tension. In the ribbon  5 , portions  51 ,  51  other than the portions corresponding to the electrode lead portions  18 ,  18  are formed in the shape of a triangular wave by being alternately folded at fixed intervals. The direction of lines formed by the folding, i.e., the direction of the lines which the top and the bottom of the triangular wave draw are the width direction of the ribbon  5 , and these lines are formed at fixed intervals. Hereinafter, both corrugated ends of the ribbon  5  are referred to as a corrugated end  51 ,  51 , respectively. Terminal strips  9 ,  9  are overlapped onto the electrode lead portions  18 ,  18 , respectively, and onto each terminal strip  9  the pressure plate  8  is overlapped sandwiching the end of the ribbon  5 . These terminal strips  9 ,  9  are electrically conducted to each end of the ribbon  5  via the pressure plates  8 ,  8  so that a signal from the ribbon microphone unit  3  may be output from each of the terminal strips  9 ,  9 . The intermediate portion in the longitudinal direction of the ribbon  5  is a corrugated intermediate portion  52 , in which the top and the bottom of a triangular wave are formed along the line (i.e., line in the longitudinal direction of the ribbon  5 ) in the direction perpendicular to the direction of lines which the top and the bottom of the triangular wave of the corrugated ends  51 ,  51  draw. The both longitudinal ends  54 ,  54  of the ribbon  5  are flat, not having corrugated irregularities formed therein. 
     The ribbon  5  vibrates in response to a sound wave and in accordance with the sound wave. This vibration direction is the direction intersecting the magnetic flux between the permanent magnets  4 ,  4 , and the ribbon  5  made of a conductor intersects the magnetic flux to thereby generate electric power, whereby an electric signal is generated between the both longitudinal ends of the ribbon  5 , accordingly between the electrode lead portions  18 ,  18 . Since this electric signal turns into a signal having a frequency and amplitude corresponding to the frequency and amplitude of the ribbon  5 , a sound wave which hits the ribbon  5  will be converted into an electric signal corresponding to the sound wave. Since the ribbon microphone is an inertia control system, the resonance frequency of the ribbon  5  needs to be no greater than the low frequency of sound waves to be collected, in other words, needs to be a frequency lower than the lowest frequency of a frequency band in which sounds can be collected. For this reason, the tension of the ribbon  5  is set extremely low. As described above, in the ribbon  5 , the corrugated ends  51 ,  51  are formed by the both ends being folded, whereby a low tension is realized. 
     In the example of the ribbon microphone described above, the intermediate portion in the longitudinal direction of the ribbon  5  is the corrugated intermediate portion  52 , in which the top and the bottom of a triangular wave are formed along the longitudinal line of the ribbon  5 . The ribbon of most of the conventional ribbon microphones is formed so that the direction of the lines, which the top and the bottom of the triangular wave draw, is the width direction of the ribbon, and the triangular wave travels across the longitudinal direction.  FIG. 7 ,  FIG. 8 , and  FIG. 9  show enlarged views of the electrode lead portion  18  having the ribbon diaphragm  5  and the pressure plate  8  in the ribbon microphone unit shown in  FIG. 6 . In  FIGS. 7A and 7B , the both longitudinal ends of the ribbon diaphragm  5  are sandwiched by the support plates  81 ,  81  and the pressure plates  8 , 8 , and are secured by fastening the both ends of the pressure plate  8  to the support plate  81  with screws  10 ,  10  respectively. As shown in  FIG. 8 , when the screw  10 ,  10  are tightly fastened, the pressure plate  8  is bend-deformed so as to surround the ribbon diaphragm  5  in the width direction, in other words, the pressure plate  8  is bend-deformed in such direction that the both ends rather than the center portion in the width direction of the diaphragm  5  come closer to the diaphragm  5 . Because the pressure plate  8  is bend-deformed in this manner, the pressure in the center portion in the width direction of the ribbon diaphragm  5  is weak and only the both ends contact the pressure plate  8 . Accordingly, the conductive resistance of the ribbon diaphragm  5  will increase. Then, as shown in  FIG. 9 , the pressure plate  8  is bent in a direction opposite to the above-described bending direction in advance, so that the ribbon diaphragm  5  may uniformly contact the pressure plate  8  when the both ends of the opposing pressure plate  8  are fastened. However, in order to deform the pressure plate  8  so that the both ends of the ribbon diaphragm  5  become flat and uniformly contact the pressure plate  8 , expert skills and experiences of the operator are required. Moreover, even if the pressure plate  8  is deformed as described above, problems as described below cannot be resolved. 
     As shown in  FIG. 10 , the both longitudinal ends  54 ,  54  of the ribbon diaphragm  5  are flat planes. In the maintenance of the ribbon microphone, when replacing the ribbon diaphragm  5 , as shown in  FIG. 6 , the both ends of the ribbon diaphragm  5  should be disposed in the electrode lead portions  18 ,  18  that are formed in the frame  7  of the ribbon microphone unit  3 . However, since the both ends  54 ,  54  of the ribbon diaphragm  5  are flat planes, they are elastically weak and wobble and thus the position in attaching the both ends  54 ,  54  to the electrode lead portion  18  becomes unstable, and the attachment work of the diaphragm becomes difficult. Moreover, if the both ends of the ribbon diaphragm  5  are disposed in the electrode lead portions  18 ,  18  and then fastened with the screws  10 ,  10  via the pressure plate  8 , a stress caused by fastening the screws  10 ,  10  transmits to the pressure plate  8  and twists the ribbon diaphragm  5 . This stress on the diaphragm does not allow the diaphragm to vibrate faithfully to sound waves. If a microscopic rotational stress due to the screw occurs, the diaphragm assembly work needs to be done again. The rate that the assembly should be carried out again is called a failure rate, and the shape of the conventional ribbon diaphragm has a drawback of increasing the failure rate at the time of assembling. 
     Next, the invention described in a patent document related to the present invention is described. The invention described in Patent Document 1 relates to a method of manufacturing a ribbon microphone, and in particular, relates to a method of manufacturing the ribbon microphone capable of adjusting the tension of the ribbon diaphragm while observing the same. In the ribbon diaphragm described in Patent Document 1, both longitudinal ends are flat planes, and corrugated irregularities are formed continuously in an intermediate portion in the longitudinal direction. The both ends of the ribbon diaphragm are flat planes, and the both flat ends are crimped between presser plates and support plates by fastening screws, respectively.
     [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-319595   

     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     As the ribbon diaphragm of the conventional ribbon microphone, there is the one, wherein in order to provide an elastic strength, i.e., stiffness, an intermediate portion in the longitudinal direction except the both longitudinal ends is formed in such a corrugated shape that a line, which the top of a wave draws, is in the longitudinal direction of the diaphragm. According to the ribbon diaphragm having such a configuration, during assembly and also during the maintenance, such as the replacement of the ribbon diaphragm, it is possible to prevent the ribbon diaphragm from folding due to external factors, such as gravity and a wind force. This has an effect of facilitating the maintenance. However, in the conventional example shown in  FIG. 5  to  FIG. 10 , and the invention described in Patent Document 1, the both ends of the ribbon diaphragm are flat and elastically weak, so the both ends of the ribbon diaphragm wobble during the assembly or maintenance and thus the operability is poor. 
     Moreover, in the ribbon diaphragm of the conventional ribbon microphone, since the both ends of the ribbon diaphragm, i.e., the electrode securing portions, are flat, a rotational stress caused by fastening the screw for securing the ribbon diaphragm causes a torsion in the ribbon diaphragm, which increases the failure rate in assembling the ribbon diaphragm. 
     In view of the prior arts described above, it is an object of the present invention to provide a ribbon microphone and a ribbon microphone unit, which can reduce a conductive resistance by forming a plurality of irregularities in the thickness direction in a portion for securing a ribbon diaphragm thereto, and thereby strengthening the contact between a secured portion of the ribbon diaphragm and a member for securing the ribbon diaphragm, and which further can facilitate the assembly of the ribbon diaphragm and the maintenance, such as the replacement, tension adjustment, or the like, by giving a rigidity to both ends of the ribbon diaphragm. 
     Means for Solving the Problems 
     According to a main feature of the present invention, a ribbon microphone unit comprises: a magnet for forming a magnetic gap; a ribbon diaphragm that is disposed inside the magnetic gap and vibrates in response to a sound wave, an electrode lead portion for outputting an electric signal that is generated by the ribbon diaphragm vibrating inside the magnetic gap; a frame provided with the magnet and the electrode lead portion; a tightening member which sandwiches both longitudinal ends of the ribbon diaphragm so as to be secured; and a screw for crimping the tightening member to the electrode lead portion of the frame, wherein the tightening member crimps the both longitudinal ends of the ribbon diaphragm by fastening a screw, the both longitudinal ends abutting against the electrode lead portion, and wherein the ribbon diaphragm includes a portion sandwiched by the tightening member, and the portion is formed in an irregular shape in the thickness direction. 
     Advantages of the Invention 
     By forming the irregularities in the thickness direction in the portion in contact with the tightening member on both ends of the ribbon diaphragm, microscopic contact is strengthened. This reduces the conductive resistance and thereby excellent acoustic characteristics can be obtained. Moreover, by giving a rigidity to the both ends of the ribbon diaphragm by forming the irregularities, the assembly of the ribbon diaphragm, and the maintenance, such as the replacement, tension adjustment, or the like, can be facilitated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example of a secured portion of a ribbon diaphragm used for a ribbon microphone according to the present invention, wherein  FIG. 1A  is an enlarged sectional view,  FIG. 1B  is an enlarged front view, and  FIG. 1C  is an enlarged side view. 
         FIG. 2  shows the ribbon diaphragm in the above-described embodiment, wherein  FIG. 2A  is a front view, and  FIG. 2B  is a side view. 
         FIG. 3  shows an intermediate process of a maintenance related to the above-described embodiment, wherein  FIG. 3A  is a front view, and  FIG. 3B  is a side sectional view. 
         FIG. 4  shows a ribbon microphone unit according to the above-described embodiment, wherein  FIG. 4A  is a front view, and  FIG. 4B  is a side sectional view. 
         FIG. 5  is a partial front sectional view showing an example of a conventional ribbon microphone. 
         FIG. 6  shows an example of a conventional ribbon microphone unit, wherein  FIG. 6A  is a front view, and  FIG. 6B  is a side sectional view. 
         FIG. 7  shows a first example of a secured portion of a conventional ribbon diaphragm, wherein  FIG. 7A  is an enlarged sectional view, and  FIG. 7B  is an enlarged side sectional view. 
         FIG. 8  is an enlarged sectional view illustrating a state where a screw is fastened in the above-described conventional example. 
         FIG. 9  is an enlarged sectional view illustrating a second example of the secured portion of the conventional ribbon diaphragm. 
         FIG. 10  shows an example of the conventional ribbon diaphragm, wherein  FIG. 10A  is a front view, and  FIG. 10B  is a side view. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of a ribbon microphone unit according to the present invention will be described with reference to the accompanying drawings.  FIGS. 4A and 4B  show an embodiment of the ribbon microphone unit according to the present invention. The ribbon microphone unit shown in  FIG. 4A  comprises a frame  7 , a magnet  4 , an electrode lead portion  18 , a terminal strip  9 , a tightening member comprising a pressure plate  8  and a support plate  81 , a screw  10 , and a ribbon diaphragm  60 . The frame  7  is formed in a rectangular frame shape that is long in the longitudinal direction, and a screw hole for securing to the microphone case  1  is formed at four corners. On the inner surface of the frame  7 , a pair of permanent magnets  4 ,  4  is fixed on both sides along the longitudinal direction, with a predetermined spacing between the both permanent magnets  4 ,  4 . The frame  7  is made of a magnetic material, functions as a yoke, and constitutes a magnetic circuit that goes out of the permanent magnets  4 ,  4  and returns to the permanent magnets  4 ,  4 . The magnetization directions of the permanent magnets  4 ,  4  are the same. Accordingly, the parallel field is formed between the permanent magnets  4 ,  4 . The ribbon diaphragm  60  is disposed within the parallel magnetic field. 
     The ribbon diaphragm  60  forms a long and slender band shape, as shown in  FIGS. 2A and 2B , and comprises, in the longitudinal direction, a corrugated center portion  152  formed in the center portion, a corrugated connecting portion  151  continuously formed on both sides of the corrugated center portion  152 , and both irregular-shaped ends  62  formed on the both longitudinal ends of the ribbon diaphragm  60  following the corrugated connecting sections  151 . The corrugated center portion  152 , the corrugated connecting portion  151 , and the both irregularly-shaped ends  62  are formed in a different corrugated shape, respectively, as follows. The corrugated center portion  152  is formed in a corrugated shape in the longitudinal direction of the diaphragm  60  as the corrugated intermediate portion  52  in the conventional example shown in  FIG. 10  is. The corrugated connecting portion  151  of the ribbon diaphragm  60  is formed in a corrugated shape in the width direction of the diaphragm  60  as the corrugated end  51  in the conventional example shown in  FIG. 10  is. The both irregularly-shaped ends  62  of the ribbon diaphragm  60  are formed in an irregular shape in the thickness direction. The irregularities of the both ends  62  are triangular wave-like irregularities formed by being alternately folded at fixed intervals, and the direction of lines, which the top and the bottom of the triangular wave draw, is the longitudinal direction of the ribbon diaphragm  60 . 
     The irregularities of the both ends  62  of the ribbon diaphragm  60  may be a plurality of stripe-like irregularities such as the illustrated example, or may be a plurality of broken-line-like irregularities. Due to the formation of the irregularities on the both ends  62 , during the assembly of the ribbon diaphragm  60  or the maintenance, such as the replacement or tension adjustment, the elasticity and rigidity of the both ends  62  can be kept strong, and also the operability of the assembly or the maintenance can be improved. Moreover, by forming the both ends  62  of the ribbon diaphragm  60  in an irregular shape, the contact to the electrode lead portion  18 , which will be described below, can be strengthened, and the electric resistance can be reduced. As long as the operability improvement in the assembly or maintenance and the reduction in the electric resistance as described above can be obtained, any irregular shape of the both ends  62  of the ribbon diaphragm  60  is employed. 
     Next, the configuration of the electrode lead portion  18  is described with reference to  FIG. 1 ,  FIG. 3  and  FIG. 4 . The both ends  62  of the ribbon diaphragm  60  are positioned in the electrode lead portion  18  of the frame  7 . The electrode lead portion  18  integrally includes support plates  81 ,  81  near the both longitudinal ends of the frame  7 , wherein each of presser plates  8 ,  8  is disposed on one side of these support plates  81 ,  81 . The support plates  81 ,  81  and the presser plates  8 ,  8  have a rectangular shape that is long in the width direction of the frame  7 , and each of the presser plates  8 ,  8  is adapted to be secured to the support plates  81 ,  81  by fastening the screw  10 , respectively. 
     Between the support plates  81 ,  81  and the presser plates  8 ,  8 , circuit boards  9 ,  9  and each of the ends  62 ,  62  of the ribbon diaphragm  60  are interposed, respectively. The both ends  62 ,  62  of the ribbon diaphragm  60  are sandwiched by the circuit boards  9 ,  9  and the presser plates  8 ,  8 , respectively. If the screw  10  is loosened to loosen the compressive force caused by the presser plates  8 ,  8 , the tension of the ribbon diaphragm  60  will be loosened. If one presser plate  8  is loosened and one side of the ribbon diaphragm  60  is pulled outwardly, a tension can be applied to the ribbon diaphragm  60 . If the screw  10  is fastened in a state where an appropriate tension is given to the ribbon diaphragm  60 , the presser plates  8 ,  8  can press the ends  62 ,  62  of the ribbon diaphragm  60  against the support plates  81 ,  81 , respectively, to secure the ribbon diaphragm  60 . The presser plates  8 ,  8  paired with each of the support plates  81 ,  81  constitute tightening members for securing the both longitudinal ends  62 ,  62  of the ribbon diaphragm  60 . 
     A predetermined circuit pattern is formed in the circuit boards  9 ,  9 , and the both ends  62 ,  62  of the ribbon diaphragm  60  are pressed against this circuit pattern, and the circuit pattern of the circuit boards  9 ,  9  and the ends  62 ,  62  of the ribbon diaphragm  60  are electrically conducted. A part of the circuit boards  9 ,  9  projects outwardly from the both longitudinal ends of the frame  7 , and electrodes  91 ,  91  are formed in these projecting portions. The electrodes  91 ,  91  function as an output terminal for sound signals, respectively. 
       FIGS. 3A and 3B  show one process of the ribbon microphone unit assembly. The both ends  62 ,  62  of the ribbon diaphragm  60  extend outwardly in the longitudinal direction of the frame  7 . In order to assemble the ribbon diaphragm  60  into the frame  7 , the both ends  62  of the ribbon diaphragm  60  are disposed in the electrode lead portion  18 , and then each of the screws  10 ,  10  inserted in a hole of each of the presser plates  8 ,  8  is screwed into each of the support plates  81 ,  81 , thereby securing the ribbon diaphragm  60 . However, the tension of the ribbon diaphragm  60  is adjusted after the fastening force by the screw  10  is loosened, and then while being adjusted to an appropriate tension, the screw  10  is fastened to secure the both ends  62 ,  62  of the ribbon diaphragm  60 . Next, a portion of each of the both ends  62 ,  62  of the ribbon diaphragm  60 , the portion extending from the presser plate  8 , is cut off. In the both ends  62 ,  62  of the ribbon diaphragm  60 , as described above, at least a portion that is sandwiched by the support plates  81 ,  81  and the presser plates  8 ,  8 , respectively, as the tightening members is formed in an irregular shape in the thickness direction. 
     According to the embodiment described above, as shown in  FIG. 1C , the both ends  62 ,  62  of the ribbon diaphragm  60  are formed in an irregular shape in the thickness direction, and thereby these become highly rigid as well as highly elastic. This stabilizes the positions of the both ends  62 ,  62  of the ribbon diaphragm  60 , and facilitates the work in securing the ribbon diaphragm  60  to the electrode lead portion  18  or the work in replacing the ribbon diaphragm  60  by the maintenance. Moreover, since both irregularly-shaped ends  62 ,  62  formed in the ribbon diaphragm  60  are highly elastic as described above, by fastening the screw  10  to the ribbon diaphragm  60  an effect of countering a rotational stress applied to the tightening member is obtained, and the torsion of the ribbon diaphragm  60  can be reduced. 
     Moreover, according to the above-described embodiment, as shown in  FIG. 1A , the both ends  62 ,  62  of the ribbon diaphragm  60  are formed in an irregular shape, and thereby the contact to the electrode lead portion  18  is strengthened. Accordingly, the contact resistance between the ribbon diaphragm  60  and the electrode lead portion  18  can be reduced, and excellent output characteristics can be obtained without degrading the acoustic characteristics of the electric signal that is generated by the ribbon diaphragm  60  cooperating with the magnetic field. 
     By assembling the ribbon microphone unit according to the above-described embodiment into a microphone case, and then providing in a microphone case a connector for outputting an output signal from the microphone unit to an external circuit, the ribbon microphone unit can constitutes a ribbon microphone.