Abstract:
A microphone has first and second differentially interconnected capsules angularly and linearly displaced from each other by a predetermined amount.

Description:
[0001]    The present invention relates in general to microphoning and more particularly concerns a novel differentially combined two-capsule microphone.  
         BACKGROUND OF THE INVENTION  
         [0002]    For background reference is made to the Microphone Handbook, pp. 81-82.  
           [0003]    It is an important object of the invention to provide an improved differentially combined dual-capsule microphone.  
         SUMMARY OF THE INVENTION  
         [0004]    A microphone according to the invention comprises differentially-combined first and second angularly and linearly displaced capsules. An advantage of the invention is reduced temporal and spectral distortion and higher gain before feedback.  
           [0005]    In one form there is a hand-held version especially suitable for vocalists, preferably constructed and arranged to fit the hand and upon standard microphone clips that in turn fit on standard microphone stands and hardware. In another form there is a stand-mount version for vocalists and instrumentalists with the acoustical element permanently attached to a microphone clip that fits standard microphone stands and hardware. In another form there is a clamp-clip embodiment constructed and arranged for attachment to musical instruments, such as wind instruments and drums. The acoustical element for the clamp-clip embodiment is typically the same as for the stand-mount version except with a microphone cable, typically about eight meters long, permanently attached to the assembly and terminating in a standard male XLR connector.  
           [0006]    In a specific form the spacing between capsules is greater than ½″. Preferably there is a puff filter on one or both capsules with the distance between puff filter and capsule being less than about ⅛″, an advantageous puff filter being disclosed in U.S. Pat. No. 4,975,966.  
           [0007]    According to an aspect of the invention, the two differentially combined capsules are constructed and arranged with variable spacing between the capsules, typically within a range of ½″ to 5″.  
           [0008]    Other features, objects and advantages of the invention will become apparent from the following detailed description when read in connection with accompany drawing in which: 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0009]    [0009]FIG. 1 is a pictorial representation of an embodiment of the invention;  
         [0010]    [0010]FIG. 2 is a schematic circuit diagram showing the differential combination of the transduced signals from the dual capsules;  
         [0011]    [0011]FIG. 3 is a simplified schematic of the microphone system;  
         [0012]    [0012]FIG. 4 shows a suitable stand with a boom and extendable shaft;  
         [0013]    [0013]FIG. 5 shows a flexible support;  
         [0014]    [0014]FIG. 6 shows a clip mount;  
         [0015]    [0015]FIG. 7 shows a hand-held arrangement;  
         [0016]    [0016]FIG. 8 is a perspective view of an actual handheld embodiment of the invention;  
         [0017]    [0017]FIG. 9 is a perspective view of an actual stand-mount embodiment of the invention;  
         [0018]    [0018]FIGS. 10A and 10B are perspective views of actual clamp mount embodiments of the invention suitable for mounting on drums and brass instruments;  
         [0019]    [0019]FIG. 11A showing the embodiment of FIGS. 10A and 10B mounted on the rim of a drum;  
         [0020]    [0020]FIG. 11B is a pictorial representation showing how the embodiment of FIGS. 10A and 10B may be mounted on the bell of a wind instrument;  
         [0021]    [0021]FIG. 12A is a side view of the embodiment shown in FIGS. 11A and 11B in the clamped position; and  
         [0022]    [0022]FIG. 12B is a side view of the embodiment shown in FIGS. 11A and 11B in the unclamped position. 
     
    
     DETAILED DESCRIPTION  
       [0023]    With reference now to the drawing and more particularly FIG. 1, there is shown a pictorial representation of an embodiment of the invention. The microphone  100  includes dual differentially-combined capsules  102  and  104  angularly and linearly displaced with capsule  102  along the axis of the cylindrical support  102  and capsule  104  perpendicular to this axis. The spacing between capsules  102  and  104  is typically 3.3 inch. A three-terminal jack  114  receives leads from capsules  102  and  104  and a common lead. Flexible extension  110  may also attach to a microphone stand, as shown in FIG. 5. A flexible extension of this type is typical of a head-worn “boom” or drummer&#39;s microphone.  
         [0024]    Referring to FIG. 2, there is shown a schematic circuit diagram of a system including the embodiment of FIG. 1. The two leads from capsules  102  are connected to terminals  3  and  1  across resistor  308 . Two leads from capsule  104  are connected to terminals  2  and  1  respectively across resistor  310 . Batteries B 1  and B 2  furnish biasing potential to capsules  102  and  104  respectively through resistors R 1  and R 2  respectively. Capacitors C 1  and C 2  couple the outputs of capsules  102  and  104  respectively to the + and − inputs of differential combiner  312  whose output is coupled to the rest of the mixer (not shown).  
         [0025]    Referring to FIG. 3, there is shown a schematic circuit diagram illustrating how outputs from capsules  102  and  104  are differentially combined. B a  and B b  are batteries supplying DC power; R a  and R b  are resistors furnishing bias to the capsules; C a  and C b  are DC blocking capacitors; and  102  and  104  are the capsules (which have internal transistor amplifier circuits inside).  
         [0026]    Referring to FIG. 4, there is shown a suitable microphone stand including a base  410  having an XLR socket  411  carrying support  110 ′ that is extendable with a boom  412  having a three-pin socket  413  for receiving the microphone. Sockets  413  and  411  are electrically connected by wires running inside the microphone stand and boom.  
         [0027]    Referring to FIG. 5, there is shown a variation of the embodiment of FIG. 4 having a flexible support  512  instead of boom  412 .  
         [0028]    Referring to FIG. 6, there is shown an embodiment with a clamp structure  712  supporting the microphone.  
         [0029]    Referring to FIG. 7, there is shown a variation of a hand-held embodiment having a handle  812 .  
         [0030]    Referring to FIG. 8, there is shown a perspective view of an actual hand held embodiment of a microphone according to the invention;  
         [0031]    Referring to FIG. 9, there is shown a perspective view of an actual stand-mount embodiment according to the invention.  
         [0032]    Referring to FIGS. 10A and 10B, there are shown perspective views of an actual embodiment of the invention suitable for clamping to the rim of a drum or the bell of a wind instrument;  
         [0033]    Referring to FIG. 11A, there is shown a pictorial view illustrating how the embodiment of FIGS. 12A and 12B may be clamped to the rim of a drum.  
         [0034]    Referring to FIG. 11B, there is shown a pictorial view illustrating how the embodiment of FIGS. 12A and 12B may be clamped to the bell of a wind instrument.  
         [0035]    Referring to FIG. 12A, there is shown a side view of a clamp mount embodiment of the invention with the jaws  1201  and  1202  closed when button  1203  is slid to the left.  
         [0036]    Referring to FIG. 12B, there is shown a side view of the clamp mount embodiment of FIG. 12A with jaws  1201  and  1202  separated when button  1203  is slid to the right.  
         [0037]    The clamp structure preferably includes a quick release feature and is adjustable so that it can attach a wide range of structures with adjustable clamping force and can accommodate a wide range of clamp widths with constant level of clamp force, if desired.  
         [0038]    A specific clamp arrangement for a wind instrument may comprise having the primary microphone capsule, such as  102  constructed and arranged so that it is oriented in the bell of the instrument, such as a brass instrument, and the canceling capsule, such as  104 , located outside the bell, away from the direct radiation path of the instrument. Stated in other words, the primary capsule is on the instrument axis, and the canceling capsule is off axis.  
         [0039]    A system according to the invention includes a plurality of dual element differential microphones, used with a plurality of line arrays for a plurality of performers. Preferably, each microphone is oriented with the axis of the target capsule perpendicular to the line arrays.  
         [0040]    A feature of an aspect of the invention resides in having the individual capsules angularly and linearly displaced. In a specific form the primary capsule is located in the head of the support structure with the auxiliary or canceling capsule located on the outer circumference of the support structure.  
         [0041]    The housing structure is constructed and arranged to encourage the user to grasp the microphone away from the location of the canceling capsule, typically by having ridges or other structures. Preferably, the geometry is arranged so that it is difficult for a user to inadvertently cover the auxiliary canceling capsule. The structure may have a recess accommodating the canceling capsule to prevent covering completely.  
         [0042]    Variable spacing between capsules may be affected with a flexible connection between the two capsules to allow for easy adjustment of the spacing between.  
         [0043]    The microphone system according to the invention typically includes a head assembly, a system of utility fixtures to which the head is attached and structure connecting the head to the fixtures, both electrically and mechanically. The head assembly has two capsules, such as  102  and  104 . In a specific form, these capsules are commercially available, Panasonic 60A92 electret elements typical of many small (4-8 mm) onmidirectional electret microphone capsules.  
         [0044]    One element, such as  102 , is the target element and the other, such as  104 , is the canceling element. The target and canceling elements are linearly spaced from each other, typically 3.30″ (a three point 8 mm). The target element is fixed to the physical end or extremity of the head assembly. A two-stage pop or puff filter is typically assembled over the acoustical entrance to the target element. In a specific form this filter is a relatively close-fitting stainless steel resistive mesh cup and then a larger 100 PPI reticulated urethane foam pop-filter that fits over the target-element/mesh assembly. In a specific form, a simple, minimum-envelope, acoustically transparent grill fits over the canceling element, or both the target and canceling elements to conceal and protect both elements and to provide an esthetically pleasing appearance.  
         [0045]    The two elements are wired out of phase as indicated above while still providing a phantom voltage (typically 48 or 24 VDC) to both in a specific form. In a specific form each element is wired to legs of a typical XLR connector.  
         [0046]    Preferably the sensitivity of the first and second capsules is substantially the same. Matching can be achieved by sorting, varying the resistance of the biasing resistors, or other suitable means so that the ratio of electrical output to acoustic pressure input for both capsules is substantially the same.  
         [0047]    Any means of providing DC bias, such as a battery or external supply and any means of providing a differential mixing circuit may be used within the principles of the invention.  
         [0048]    Parallel dropping resistors furnish specific phantom voltages less than 48 or 24 VDC for both microphone elements. An acoustic signal, such as a human voice, that is close to the target element provides a transduced signal that is greater than that generated by the relatively distant canceling element and passes through the microphone system as the dominant target-generated signal. The far-field signals that arrive at both elements with substantially the same sound pressure level produce canceling transduced signals.  
         [0049]    There has been described novel apparatus and techniques for microphoning. It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific apparatus and techniques herein disclosed without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of the appended claims.