Patent Publication Number: US-7912241-B1

Title: Field serviceable planar loudspeaker

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to planar-magnetic loudspeakers and more particularly to a push-pull, planar-magnetic loudspeaker allowing field replacement of the diaphragm. 
     2. Description of the Problem 
       FIG. 1  illustrates a double-ended, or push-pull, magnetic-planar transducer  20 , conventional in the prior art. This structure is characterized by two magnetic arrays  10  and  11  supported by perforate substrates  14 ,  24  positioned on opposite sides of a flexible diaphragm  12 , which includes a conductive coil  13 . The film is tensioned into a planar configuration. An audio frequency drive signal is supplied to the coil  13 , and a variable voltage and current thereby provided in the coil gives rise to a variable magnetic field, which interacts with the fixed magnetic field set up by and between the magnet arrays  10  and  11 . The diaphragm is displaced in accordance with the audio frequency drive signal, thereby generating a desired acoustic output. An example representing this art area is found in U.S. Pat. No. 4,156,801 issued to Whelan. 
     Because of a doubled-up, front/back magnet layout of the prior art push-pull magnetic structures, double-ended systems have been generally regarded as more efficient, but also as more complex to build. Double-ended designs are also particularly sensitive to deformation from repulsive magnetic forces that tend to deform the devices outward. Outward bowing draws the edges of the diaphragm closer together, and alters the tension of the diaphragm. This can seriously degrade performance and, over time, can render the speaker unusable necessitating disposal or repair of the unit. 
     Assembly of push-pull structures presents its own difficulties. As observed in U.S. Pat. No. 6,934,402 issued to Croft III, et al., the magnetic circuits of the front and back magnetic structures interact. The repulsion forces make it difficult to have a stable mechanical structure, while providing a focused field and making better use of magnetic material than single-ended devices. Assembly of push-pull structures presents its own difficulties. Like magnetic poles are brought into close proximity, requiring substantial force to bring the assembly together. 
     In U.S. Pat. No. 5,850,461 it was further observed that in the field of planar magnetic acoustic transducers and related flat type transducers utilized for sound reproduction, the tensioning of the sound producing diaphragms is important to obtain uniform sound reproduction. The proper tensioning of a diaphragm within a support frame has created difficulty in manufacturing processes. In planar magnetic transducers, if sufficient diaphragm tensioning is not provided, the diaphragm may vibrate into one of the stators formed by spaced magnets mounted within a support frame in spaced relationship with respect to an electrical circuit applied to the diaphragm. Improper tensioning throughout the diaphragm also results in changes in the vibrational characteristics of the diaphragm throughout its “sound producing” or “active” area which is generally that area defined internally of the diaphragm support frame. 
     SUMMARY OF THE INVENTION 
     According to the invention a push-pull, planar-magnetic acoustic transducer comprises a front panel incorporating an array of magnets set in an aperture and a back panel including an array of magnets set in an aperture, where upon assembly the front and back panels are held parallel to one another in close proximity with like polarity poles of the magnets aligned on one another. The front and back panels are coupled together along one major side of each on a pivot/hinge bar. The pivot bar extends through slots in alternating sections of the front and back panels where the slots through the sections of one of either the front or back panels are elongated in the front to back direction of the panel. Set screws are fitted to hold the front and back panels together in the facing, parallel assembly. 
     Additional effects, features and advantages will be apparent in the written description that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional fragmentary view of a prior art push-pull planar-magnetic transducer; 
         FIG. 2  is a perspective view of a planar magnetic transducer according to the invention opened for replacement of its diaphragm; 
         FIG. 3  is a top plan view of a planar-magnetic transducer in accordance with the invention; 
         FIG. 4  is a top plan view of a diaphragm for the planar-magnetic transducer of  FIG. 3 ; 
         FIG. 5  is a top plan view of a base plate for the planar-magnetic transducer of  FIG. 3 ; 
         FIG. 6  is a cross sectional view of the planar-magnetic transducer of  FIG. 3  taken along section lines  6 - 6 ; 
         FIG. 7  is a cross sectional view of the planar-magnetic transducer with set screws released; and 
         FIG. 8  is a cross sectional view of the planar-magnetic transducer opened for replacement of a diaphragm. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures and in particular to  FIG. 2  an opened clam shell  30  for use in constructing a double-ended, or push-pull, magnetic-planar transducer is shown. Clam-shell  30  comprises a front panel  22  and a back panel  24  which are linked by a hinge structure  42  along one of major (i.e. longer) edges of each panel. Front panel  22  and back panel  24  include central apertures  40  and  38  respectively, in which may be placed any preferred arrangement of magnets. Central apertures  40 ,  38  connect opposite major surfaces of the front and back panels  22 ,  24 . A diaphragm  26  (shown more particularly in  FIG. 4 ) for introduction to the clam shell  30  as indicated by arrows A is placed on the forward major surface  28  to be pressed between the front panel  22  and back panel  24  upon closure of clam shell  30 . 
     An important characteristic of front and rear panels  22 ,  24  are threaded holes  34 ,  32 , visible on the rearward facing major surface  23  and the forward facing surface  28  of the front and back panels, respectively. Upon assembly the alignment holes  36  of diaphragm  26  align on and between threaded holes  34 ,  32 . Upon placement of diaphragm  26  on the forward face  28  alignment holes  36  must be brought into precise alignment with alignment holes  32 . 
     Hinge  42  is constructed between interlaced blocks  44 ,  46 . Four blocks  44  extend downwardly from rearward surface  23  into gaps  67  between blocks  46  extending outwardly from the relatively rear surface of back panel  24 . In this way the blocks  44 ,  46  of the respective panels alternate in sequence along a major edge of each of the panels. The hinge itself, as described below, allows the front panel  22  to translate or move front to back or back to front a short distance while the panels remain in a flat, parallel orientation with respect to each other. That is to say, the direction of movement of the front panel  22  may upon opening be kept perpendicular to the panel&#39;s major surfaces for a short distance. Conversely, upon closure, the front panel  22  may be brought into a parallel, facing position with the back panel  24  manually at a spacing where the repulsive force generated by the magnets is not too strong to prevent such movement. 
     Referring to  FIG. 3 , a planar-magnetic transducer  18  is shown constructed in accordance with the invention from clamshell  30 . Bar magnets  52  are placed in aperture  40  and the clamshell  30  is held closed by set screws threaded into the alignment holes  34 ,  32  of the front and back panels  22 ,  24 . Front panel  22  is linked to back panel  24  by a hinge bar  54  located in the gaps  67  between the blocks  46  and which passes through blocks  44 . The relatively elongated heads  50  of the set screws enables turning the set screws to bring the front and back panels  22 ,  24  into closer proximity against the strong repulsive force of the magnets. 
     Referring to  FIG. 5 , a hinge bar  54  is shown inserted through slots  55  in blocks  46  of back panel  24 . Normally the hinge bar  54  is normally inserted to attach a front panel to the back panel. Magnets  56  are also illustrated placed in aperture  38 . 
     Referring to  FIG. 6  planar-magnetic transducer  18  is shown in a cross sectional view with front panel  22  clamping diaphragm  26  against rear panel  24 . The panels are held against each other by ten set-screws  58  which have been inserted into alignment holes  34  and tightened only fully inserted. In order to maintain the panels in a nearly parallel alignment, and to enable closure of the panels against one another against the repulsive force generated by the magnets  56 ,  58 , the pitch of the threads is shallow and the screws are inserted nearly synchronously, or in alternating partial turns. An oblong or elongated slot  60  is visible through block  44  into which hinge bar  54  has been inserted. When panel  22  is fully pressed against diaphragm  26  and back panel  24 , hinge bar  54  is pressed against the “upper” end of the elongated slot  60 . It will be understood that bar  54  corresponds almost exactly in diameter to slot  55  through blocks  46 . The direction of elongation is parallel to the front to back direction of the panel in the assembled transducer  18 . 
     With removal of threaded set-screws  58  front panel  22  moves away from back panel  24 , as is shown by the gap between diaphragm  26  and front panel  22 , and by the illustration of hinge bar  54  being located at the bottom of elongated slot  60  as shown in  FIG. 7 . It is desirable for assembly and disassembly that C-clamps or similar devices are used as restraints while the set screws are inserted and removed do to the powerful repulsive forces generated by the opposed magnets. As illustrated in  FIG. 8 , this allows top panel  22  to be pivoted away from back panel  24 . 
     The invention provides a field serviceable push-pull magnetic-planar transducer which allows field replacement of diaphragms. 
     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.