Abstract:
An apparatus and method for optimizing a parametric emitter system having a pot core inductive device coupled between an amplifier and emitter. The pot core inductive device allows for adjustments of the air gap formed between the two halves of the pot core structure to adjust its inductive value. This post-manufacture adjustability allows for corrections of differences caused by operations of other components in the audio system and to account for slight differences in the electrical circuit of different amplifier/emitter combinations. As efficiency of the system is dependent on the functional relationship between the amplifier, inductive device, and emitter, this allows for fine tuning of the signal to obtain high quality.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of and claims priority to U.S. patent application Ser. No. 14/035,789, filed on Sep. 24, 2013, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to parametric audio systems. More particularly, some embodiments relate to inductive devices employed with ultrasonic emitters. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    Non-linear transduction results from the introduction of sufficiently intense, audio modulated ultrasonic signals into an air column. Self-demodulation, or down-conversion, occurs along the air column resulting in the production of an audible acoustic signal. This process occurs because of the known physical principle that when two sound waves with different frequencies are radiated simultaneously in the same medium, a modulated waveform including the sum and difference of the two frequencies is produced by the non-linear (parametric) interaction of the two sound waves. Parametric audio reproduction systems produce sound through the heterodyning of two acoustic signals in a non-linear process that occurs in a medium such as air. The acoustic signals are typically in the ultrasound frequency range. The non-linearity of the medium results in acoustic signals produced by the medium that are the sum and difference of the acoustic signals. Thus, two ultrasound signals that are separated in frequency can result in a difference tone that is within the 60 hz to 20,000 Hz range of human hearing. 
         [0004]    While the theory of non-linear transduction has been addressed in numerous publications, commercial attempts to capitalize on this intriguing phenomenon have largely failed. Most of the basic concepts integral to such technology, while relatively easy to implement and demonstrate in laboratory conditions, do not lend themselves to applications where relatively high volume outputs are necessary. As the technologies characteristic of the prior art have been applied to commercial or industrial applications requiring high volume levels, distortion of the parametrically produced sound output has resulted in inadequate systems. Whether the emitter is a piezoelectric emitter or PVDF film or electrostatic emitter, in order to achieve volume levels of useful magnitude, conventional systems often required that the emitter be driven at intense levels. These intense levels have often been greater than the physical limitation of the emitter device, resulting in high levels of distortion or high rates of emitter failure, or both, without achieving the magnitude required for many commercial applications. 
         [0005]    Efforts to address these problems include such techniques as square rooting the audio signal, utilization of Single Side Band (“SSB”) amplitude modulation at low volume levels with a transition to Double Side Band (“DSB”) amplitude modulation at higher volumes, and recursive error correction techniques. While each of these techniques has proven to have some merit, they have not separately, nor in combination, allowed for the creation of a parametric emitter system with high quality, low distortion, and high output volume. The present inventor has found, in fact, that under certain conditions some of the techniques described above actually cause more measured distortion than does a refined system of like components without the presence of these prior art techniques. 
       SUMMARY 
       [0006]    Embodiments of the technology described herein include a pot core inductive device for use in ultrasonic audio systems. Although the embodiments are discussed in regards to ultrasonic audio systems, the embodiments are applicable for use in any system requiring an inductive device; particularly systems where electrical resonance is important for optimal performance. In various embodiments, the device includes a non-conductive or ferromagnetic housing composed of an iron or ferrite material and comprising two sections, a coil support member, a coil structure, and an elastomeric material. The two sections of the housing are configured to define a cavity within the housing. The coil support member and elastomeric material are disposed within the cavity. The device also comprises an adjustment mechanism configured to adjust an air gap, formed between the two sections of the housing, to achieve an optimal or near optimal inductive value. An adjustable means for securing the two halves may also be present. 
         [0007]    Other features and aspects of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features in accordance with embodiments of the invention. The summary is not intended to limit the scope of the invention, which is defined solely by the claims attached hereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict typical or example embodiments of the invention. These drawings are provided to facilitate the reader&#39;s understanding of the invention and shall not be considered limiting of the breadth, scope, or applicability of the invention. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale. 
           [0009]    Some of the figures included herein illustrate various embodiments of the invention from different viewing angles. Although the accompanying descriptive text may refer to such views as “top,” “bottom,” or “side” of an apparatus, such references are merely descriptive and do not imply or require that the invention be implemented or used in a particular spatial orientation unless explicitly stated otherwise. 
           [0010]      FIG. 1  is a diagram illustrating an ultrasonic sound system suitable for use with the inductive device described herein. 
           [0011]      FIG. 2  is a diagram illustrating an amplifier and emitter system utilizing a pot core inductive device in accordance with an embodiment of the technology disclosed herein. 
           [0012]      FIG. 3  is a diagram illustrating an amplifier and transducer system utilizing a pot core inductive device in accordance with an embodiment of the technology disclosed herein. 
           [0013]      FIG. 4  is a diagram illustrating an amplifier and transducer system utilizing a pot core inductive device in accordance with an embodiment of the technology disclosed herein. 
           [0014]      FIG. 5  is a cross-sectional view of a typical pot core structure. 
           [0015]      FIG. 6  is a flow diagram illustrating a method of optimizing a parametric transducer system in accordance with an embodiment of the technology disclosed herein. 
           [0016]      FIG. 7  is a cross-sectional view of a pot core inductive device in accordance with an embodiment of the technology disclosed herein. 
           [0017]      FIG. 8  is a diagram illustrating an exploded view of a pot core inductive device in accordance with an embodiment of the technology disclosed herein. 
           [0018]      FIG. 9  is a diagram illustrating a pot core structure in accordance with an embodiment of the technology disclosed herein. 
           [0019]      FIG. 10  is a diagram illustrating an assembled pot-core conductor in accordance with one embodiment of the technology disclosed herein. 
           [0020]      FIG. 11  is a diagram illustrating an assembled pot-core conductor in accordance with one embodiment of the technology disclosed herein. 
       
    
    
       [0021]    The figures are not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration, and that the invention be limited only by the claims and the equivalents thereof. 
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0022]    The present disclosure represents an improvement on a transducer system for use in ultrasonic audio production described in U.S. Pat. No. 8,391,514, issued Mar. 5, 2013 to the present inventor, which is herein incorporated by reference. Transducers convert a signal from one form of energy to another. In ultrasonic audio production, an audio system comprises an amplifier, processor circuitry, an inductive device, and an emitter coupled in an electrical circuit to convert an electrical signal into an acoustic signal, or sound. As discussed above, the present inventor discovered that many of the conventional methods for increasing the output of an ultrasonic emitter created greater distortion in the resultant audio signal. This distortion makes creation of a high quality parametric audio system difficult. 
         [0023]    The present inventor discovered that by redesigning the transformer, electrical resonance could be achieved between an inductive device and an emitter, increasing the accuracy of the match between the electronic circuits and the emitters, thus eliminating much of the distortion resulting from physical limitations of conventional transducer devices. In one embodiment of the invention of U.S. Pat. No. 8,391,514, the invention utilized an inductive device housed within a pot core structure. Use of a pot core allowed for the inductive device to be physically located closer to the emitter, allowing the system to operate at a more efficient level by reducing the interference of the magnetic field of the inductive device with the emitter. At the same time, physically locating the inductive device closer to the emitter reduced the need for long runs of high voltage wiring to couple the inductive device to the emitter. 
         [0024]    Although the patented design allowed for the production of a higher quality ultrasonic audio signal, the conventional design of a pot core structure limited the ability to fine-tune the resonant circuit for optimal audio output. The improvements described herein can be configured to provide a more responsive transducer to achieve the optimal output audio signal. 
         [0025]      FIG. 1  illustrates a non-limiting signal processing system  10  that may be used with an embodiment of the invention. In this embodiment, various processing circuits or components are illustrated in the order (relative to the processing path of the signal) in which they are arranged according to one implementation. It is to be understood that the components of the processing circuit can vary, as can the order in which the input signal is processed by each circuit or component. The processing  10  can include more or fewer components or circuits than those shown. 
         [0026]    A stereo audio signal enters the signal processing system  10  through audio inputs  12   a ,  12   b . The source of the audio signal may be a microphone, memory, a data storage device, streaming media source, CD, DVD or other audio source. The audio content may be decoded and converted from digital to analog form, depending on the source. Equalizing networks  14   a ,  14   b  provide equalization of the signal. The equalization networks can, for example, boost or suppress predetermined frequencies or frequency ranges to increase the benefit provided naturally by the emitter/inductor combination of a transducer device. 
         [0027]    Compressor circuits  16   a ,  16   b  compress the dynamic range of the incoming signal, effectively raising the amplitude of certain portions of the incoming signals and lowering the amplitude of certain other portions of the incoming signals. More particularly, compressor circuits  16   a ,  16   b  can be included to narrow the range of audio amplitudes. In one aspect, the compressors lessen the peak-to-peak amplitude of the input signals by a ratio of not less than about 2:1. Adjusting the input signals to a narrower range of amplitude can be done to minimize distortion, which is characteristic of the limited dynamic range of this class of modulation systems. The order of the compression and equalization circuits can be reversed. 
         [0028]    Low pass filter circuits  18   a ,  18   b  can be included to provide a cutoff of high portions of the signal. High pass filter circuits  20   a ,  20   b  can provide a cutoff of low portions of the audio signals. The high pass filters  20   a ,  20   b  can be configured to eliminate low frequencies that, after modulation, would result in deviation of carrier frequency (e.g., those portions of the modulated signal that are closest to the carrier frequency). Also, some low frequencies are difficult for the system to reproduce efficiently and, as a result, much energy can be wasted trying to reproduce these frequencies. The low pass filters  18   a ,  18   b  can be configured to eliminate higher frequencies that, after modulation, could result in the creation of an audible beat signal with the carrier. 
         [0029]    After passing through the low pass and high pass filter circuits, modulators  22   a ,  22   b  modulate the audio signals with a carrier signal generated by oscillator  23 . Use of a single oscillator to drive both modulators  22   a ,  22   b  allows an identical carrier frequency to be used for multiple channels, lessening the risk that any audible beat frequencies may occur. High pass filters  27   a ,  27   b  can be used to pass the modulated ultrasonic carrier signal to filter out remaining unwanted signals below a certain frequency. The resultant signal then reaches the amplifier through signal processing system outputs  24   a ,  24   b.    
         [0030]      FIG. 2  is a diagram illustrating an amplifier and emitter system utilizing a pot core inductive device in accordance with an embodiment of the technology disclosed herein. Referring now to  FIG. 2 , the diagram illustrates an amplifier  26   a , a pot core inductor  28   a  (configured as a transformer in this example), and an ultrasonic emitter  3   a  four one channel of the audio system. Many conventional systems utilize a transducer system with an inductive device oriented in series with the emitter. The disadvantage to this arrangement is that such a resonant circuit must necessarily cause wasted current to flow through the inductor. The emitter  30   a  will perform best at—or near—the point where electrical resonance is achieved in the circuit. The amplifier (e.g., amplifier  26   a  in  FIG. 2 ), however, introduces changes in the circuit, which can vary based on factors including temperature, signal variance, and system performance. These effects make it more difficult to achieve and maintain stable resonance in the circuit when an inductor is coupled in series with the emitter  30   a  ( FIG. 2 ). 
         [0031]    A variety of inductive devices are known to those having ordinary skill in the art. Physical limitations of inductive devices, however, cause difficulties in a conventional parametric system. Inductive devices generate magnetic fields, which may “leak” beyond the confines of the inductor. Accordingly, they may interfere with the operation and response of a parametric emitter if positioned in proximity thereto. 
         [0032]    For at least these reasons, most conventional parametric systems physically locate the inductive device a considerable distance from the emitter. This distance between the inductive device and the emitter requires longer wires for connecting the inductive device and emitter. A significant complication resulting from this physical limitation arises from the fact that a high voltage is generally required to carry the signal from the inductive device to the emitter. In certain installations, long “runs” of high voltage wiring may be necessary, which can be dangerous and interfere with communication systems not related to the transducer. 
         [0033]    The relationship between the amplifier and the emitter adds an additional obstacle to designing an optimized and efficient transducer. Generally, the higher a frequency that is processed by an amplifier, the higher impedance at which the amplifier is best suited to operate. In the present case, the impedance experienced by the amplifier is the result of the load introduced by the inductive device and emitter pair, and by the overall transducer. In the case of parametric sound production, the operative signal is generally in the range of 40 kHz or greater. Amplifiers working with frequencies in this range generally operate more optimally when experiencing load impedances on the order of 8-12 Ohms. 
         [0034]    To account for this, it would be desirable to match the resonance of the inductive device and emitter pair to improve the performance of the system. Limited available parametric emitter designs, however, hinder the ability to adjust the load presented by the inductive device and emitter pair. This, in turn, hinders the ability to obtain optimum resonance between the inductive device/emitter pair without adversely affecting performance of the unit as a whole. 
         [0035]    The present inventor discovered and invented several amplifier and emitter systems utilizing an inductive device coupled in parallel with the emitter. Exemplary systems are described in detail in U.S. Pat. No. 8,391,514, which is incorporated herein by reference in its entirety. By configuring the inductive device in parallel with the emitter, the current circulates through the inductive device and emitter, as represented by circulating current path  40  in  FIG. 2 . Such a configuration results in more stable and predictable performance of the emitter, and significantly less power being wasted as compared to conventional series resonant circuits. 
         [0036]    Use of a “pot core” to house the inductive device further alleviates the need for the inductive device to be physically located a distance from the emitter. It is possible to capitalize on the characteristics of a pot core structure to create achieve electrical resonance in the inductive device/emitter circuit, while simultaneously achieving sufficient impedance for optimal operation of the amplifier. Although not optimal, use of a pot core inductive device in accordance with the present invention may also be coupled in series with the emitter. 
         [0037]      FIG. 5  illustrates a cross sectional view of one embodiment of a pot core structure in accordance with the technology described in U.S. Pat. No. 8,391,514. The inset at the bottom right of the drawing illustrates an external view of the 2 halves shown in the example of  FIG. 5 . 
         [0038]    Two ferrite halves  50 ,  51  define a cavity  52  within which an inductive device is disposed. Current passing through the inductive device generates a magnetic field, which could interfere with the functionality of the emitter. The ferrite material of the pot core halves  50 ,  51  serves to contain this magnetic field so that it does not “leak” into the system and cause distortion. Although ferrite is the most common material for pot core structures, the structure may be composed of other materials, such as vitreous metal, carbonyl iron, laminated silicon steel, or any other material capable of shielding magnetic fields. The selection of the pot core material depends on a number of factors, including but not limited to the geometry of the core, the potential size of the air gap, and the permeability of the material chosen. 
         [0039]    The two halves  50 ,  51  each comprise and outer wall  53   a ,  53   b  which substantially encloses the inductive device, and an inner wall  53   b ,  54   b . An air gap  55  between the inner walls  53   b ,  54   b  increases the permeability of the pot core: the larger the air gap  55 , the greater the permeability. The number of windings of the inductive device (wound about the core formed by inner walls  53   b ,  54   b ) required to maintain the same inductance, however, increases with the size of the air gap  55 . At the same time, this greater number of windings increases the impedance of the system. Therefore, by adjusting the air gap  55  in the pot core, one can maintain the same inductance to achieve electrical resonance with the emitter while simultaneously increasing the load seen by the amplifier, i.e. increasing the impedance of the system. 
         [0040]      FIG. 2  illustrates one embodiment of a transducer system disclosed in U.S. Pat. No. 8,391,514 and applicable for use with an embodiment of the present invention. Signal processing system outputs  24   a ,  24   b  are coupled to an amplifier  26   a . After amplification, the signal is delivered to an inductive device/emitter assembly  32   a . The emitter  30   a  is operable at ultrasonic levels. The inductive device  28   a  is coupled in parallel with the emitter  30   a . The inductive device  28   a  in this embodiment is an inductor element held within a pot core. 
         [0041]      FIG. 3  illustrates another embodiment of a transducer system disclosed in U.S. Pat. No. 8,391,514, wherein a transformer configuration is employed. The transformer  39  comprises a pair of inductor elements. The inductor element, or winding,  42  serves as the primary winding of the transformer and is connected to the amplifier  26   a . The inductor element, or winding,  41  serves as the secondary winding of the transformer and is connected to the emitter  30   a . As current passes through the primary winding  42  a voltage is induced in the secondary winding  41 . In one embodiment, both the primary and secondary windings are contained within the pot core. 
         [0042]      FIG. 4  illustrates another embodiment, wherein the primary and secondary windings are combined in what is commonly known as an autotransformer  39 ′, showing the secondary winding  41 ′ and the primary winding  42 ′ contained in a single winding. The operation and function of an autotransformer will be readily appreciated by one of ordinary skill in the art having possession of this disclosure. The autotransformer can be configured such that its windings can easily be contained within the pot core. 
         [0043]    The use of a step-up transformer provides additional advantages to the present system. Because the transformer “steps-up” from the direction of the amplifier to the emitter, it necessarily “steps-down” from the direction of the emitter to the amplifier. The step-down process, minimizing the effect of any such event on the amplifier and the system in general, therefore reduces any negative feedback that might otherwise travel from the inductor and emitter pair to the amplifier. 
         [0044]    The characteristics and dimensions of the pot core structure and inductive device utilized in U.S. Pat. No. 8,391,514 can be determined in accordance with the exemplary method of optimizing a parametric system illustrated in  FIG. 6 . The method is applicable with the presently disclosed technology, as well. The first step  60  is determining the number of turns in the primary winding required to obtain the impedance load that is best for optimal amplifier performance. Once the number of windings required is known, the pot core structure may be designed to take advantage of the size of the air gap, as discussed above. For embodiments of the present invention that are configured to act as an inductor only—and, therefore, have only one winding—the first step  60  is not applicable and, instead, one would start on the second step  62 . The second step  62  is to select the number of turns required in the secondary winding required to achieve electrical resonance between the secondary winding and the emitter. The third step  64  is to determine the optimal physical size of the pot core to contain the inductive device. The form factor of the entire parametric audio system will influence the size limitations of the device. The fourth step  66  is to select a size of the air gap  55  between the inner walls  54   a ,  54   b  required to decrease the overall physical size of the pot core while avoiding saturation of the inductive device during operation of the emitter, and to fine tune the inductive device. 
         [0045]    In the typical pot core structure utilized in embodiments of U.S. Pat. No. 8,391,514, the determination of the fourth step  66  cannot be changed once the pot core structure has been manufactured. As a result, any distortion of the resultant signal caused by imperfections in the transducer circuit or unforeseen artifacts from miscalculation of the required number of turns cannot be addressed without re-manufacturing the structure. The presently disclosed technology improves upon the typical pot core structure, allowing for adjustments in the size of the air gap  55  in the pot core structure to compensate for these types of distortions. This adjustment allows for additional tuning of the audio system to achieve the optimal sound, with reduced distortion caused by the intense levels at which ultrasonic emitters are operated. 
         [0046]    In various embodiments, the pot core inductive device includes an adjustment mechanism that allows adjustment of the air gap.  FIG. 7  is a cross-sectional view of an example embodiment providing such adjustability.  FIG. 8  is a diagram illustrating an exploded view of a pot core inductive device such as that shown in  FIG. 7 . Like the typical pot core structure, the structure in this embodiment comprises two halves  70 ,  71  that define a cavity  72 . Although ferrite is the most common material for pot core structures, use of other suitable materials is possible, as discussed above. Each half  70 ,  71  comprises an outer wall  73   a ,  74   a  and an inner wall  73   b ,  74   b . Disposed inside the cavity  72  is a coil support structure  75 . A coil structure, or inductor element,  76  is wound around the coil support structure  75 . This coil structure  76  can be configured as an inductor, transformer, or autotransformer. The type of coil structure  76  utilized will depend on the type of inductive device is optimal for the user, depending on desired performance, cost of construction, and level of quality of the resultant audio signal. The air gap  77  is formed in the void between the inner walls  73   b ,  74   b  of the two halves  70 ,  71 . 
         [0047]    In various embodiments, an adjustment mechanism  78  is provided to adjust the positions of halves  70 ,  71  relative to one another. For example, the adjustment mechanism can be provided to allow adjustment or setting of the spacing between halves  70 ,  71 . In other words, the adjustment mechanism can be used to adjust the volume of cavity  72  and the air gap  77  formed between inner walls  73   b ,  74   b . In some embodiments, an additional air gap  79  may be formed between outer walls  73   a ,  74   a , which may also be adjusted by the adjustment mechanism  78 . In other embodiments, the two halves  70 ,  71  may be constructed such that a projection  85  from the outer wall of one half  73   a  slots inside the outer wall of the other half  74   a , such that the cavity  72  is completely enclosed by the outer walls  73   a ,  74   a . An example of this is illustrated in  FIG. 9 . 
         [0048]    Adjustment mechanism  78  can comprise any of a number of mechanisms to allow the halves  70 ,  71  to be adjusted relative to one another. Preferably, the adjustment mechanism  78  also allows the positioning to be maintained over time, for example by using an elastomeric member  80  to maintain pressure against the adjustment mechanism as explained below. 
         [0049]    In the example illustrated in  FIG. 7 , adjustment mechanism  78  can include a male threaded member  81  configured to mate with a female threaded member  82  to adjust the spatial relation of halves  70 ,  71 . Tightening the threaded members  81 ,  82  would cause halves  70 ,  71  to move closer together and close the air gap  77 , while loosening threaded members  81 ,  82  would cause halves  70 ,  71  to move farther apart thereby widening the air gap  77 . 
         [0050]    In yet another embodiment, the adjustment mechanism  78  can comprise a threaded elongated member (e.g., a bolt or other like configuration) and the inner walls  73   b ,  74   b  can be provided with complementary threads so that female threaded member is not required. The threads presented by half  71  can be threaded in reverse as compared to the threads presented by half  70  such that, turning threaded member  81  causes halves  70 ,  71  to move in opposite directions to or from one another. In another embodiment, only one half is threaded, and it can be moved along threaded member  81  relative to the other half. 
         [0051]    In various embodiments, an adjustable means for securing the two halves may be used. The adjustable means may comprise a clamp attached externally to the two halves  70 ,  71 , or similar structures. Means may also include locking channels disposed on the external sides of the two halves  70 ,  71  that function to hold the halves  70 ,  71  together, or similar structures. In some embodiments, the adjustment mechanism  78  and the adjustable means for securing the two halves  70 ,  71  may be the same component. 
         [0052]    The components of the adjustment mechanism can be made from a nonconductive, ferromagnetic material so as not to interfere with the electrical properties of the transductor. For example, the components of the adjustment mechanism can be made from various plastics, polyester, nylon, phenolic, and other nonconductive materials. 
         [0053]    In embodiments where the spacing between halves  70 ,  71  are fixed at a known predetermined dimension, coil support structure  75  can be dimensioned to have a tight fit within the cavity  72 . However, where the spatial relation between halves  70 ,  71  is adjustable (such as, for example, via an adjustment mechanism  78 ) coil support structure  75  cannot be dimensioned for a tight fit within the cavity  72  throughout the range of adjustment. Accordingly, elastomeric member  80  can be included to provide a snug or tight fit for support structure  75  within cavity  72 . Elastomeric member  80  can be provided at a thickness so as to prevent support structure  75  from moving inside the cavity  72 . 
         [0054]    In various embodiments, elastomeric member  80  can be disposed on a first inner surface  83  of cavity  72  and be configured to expand to apply pressure on coil support structure  75  against the opposite inner surface  84  of cavity  72 . In other embodiments, to elastomeric members  80  can be provided, one on each of the top and bottom inner surfaces. For example, as illustrated in  FIG. 7 , elastomeric member  80  is placed in the bottom of cavity  72 , on inner surface  83 , and is configured to expand in height, H, to hold coil support structure  75  against the upper inner surface  84  of cavity  72 . Elastomeric member  80  is further configured to be compressible in the dimension H such that when the adjustment mechanism  78  is adjusted to bring halves  70 ,  71  closer together, elastomeric member  80  compresses (decreases in height, H), allowing the height of the cavity  72  to be decreased. Conversely, when the adjustment mechanism  78  is adjusted to increase the separation between halves  70 ,  71 , elastomeric member  80  can expand in height, H, maintaining a tight fit of coil support structure  75  within cavity  72 . In other embodiments, one or more elastomeric members  80  may be positioned in the top or bottom of cavity  72 . Still further embodiments could employ more than one elastomeric member  80 , with at least one disposed in each of the bottom and top of cavity  72 . The elastomeric member(s)  80  may be secured in place using a glue, epoxy, tape, or other nonconductive adhesives or fixation mechanisms. In other embodiments, the elastomeric member  80  could be designed as a removable element to allow repair or replacement of the elastomeric member  80 , or to allow a selectable number of members  80  to be utilized. 
         [0055]    In further embodiments, elastomeric member  80  can be configured to provide sufficient expansive force to cause halves  70 ,  71  to exert pressure against the adjustment mechanism  78  to maintain spatial relation there between as set by the adjustment mechanism  78 . In this respect, elastomeric member  80  can be configured to act like a spring applying an outward pressure against halves  70 ,  71  against the adjustment mechanism  78 . Elastomeric member  80  can be ring- or donut-shaped to conform to the inner dimensions of half  70  (or  71 ) on the lower surface of cavity  72 . Elastomeric member  80  can be made using open- or closed-cell foams or other elastomeric materials having a spring-like property. Preferably, elastomeric member  80  is made of a nonconductive material so as to not interfere with the electrical characteristics of the inductive device. 
         [0056]    As the above-described example embodiments illustrate, the pot core inductive device may include an adjustment mechanism, which can be configured to allow the air gap  77  to be increased or decreased to tune its inductance and achieve resonance with the emitter. 
         [0057]    Employing the pot core inductive device in place of a typical pot core structure allows tuning of the amplifier and emitter system. This can be particularly useful, for example, in situations where other components of the audio system might not be tightly controlled. For example, the coil structure  76  within support structure  75  may come from the manufacturer or supplier to varying degrees of tolerance. In situations where the air gap  77  and the relation between halves  70 ,  71  is fixed, variations in the coil structure  76  from one device to the next will result in variations in the inductance value from one device to the next. This, in turn, can impact the ability of these devices to create a resonant circuit with the emitter. Accordingly, providing an adjustable inductive device, with an adjustment mechanism  78  allows the inductance value to be brought to specification to account for variations in the coil structure  76 . 
         [0058]    After selecting the pot core in accordance with the method illustrated in  FIG. 6 , dynamic adjustments are possible by changing the air gap  77  in response to distortion in the audio signal. When the air gap  77  needs to be decreased, the adjustment mechanism  78  compresses the elastomeric material  80  to allow the two halves  70 ,  71  to adjust the size of the air gap  77 . When the air gap  77  needs to be increased, the adjustment mechanism  78  is reversed and the elastomeric material  80  decompresses, allowing the two halves  70 ,  71  to move apart and increase the size of the air gap  77 . 
         [0059]    In various embodiments, the transductor half  71  and member  82  may be secured such that they do not need to be separately held in place when adjustment mechanism  78  is turned to adjust the spacing. For example, transductor half  71  can be glued, adhered, affixed with screws or other fasteners, or otherwise secured to the printed circuit board on which it is mounted so that it doesn&#39;t rotate in response to torque applied to adjustment mechanism  78 . Similarly, member  82  could likewise be secured to the printed circuit board. Alternatively, member  82  could be disposed in a complementary recess (not shown) in transductor half  71  to hold member  82  in place when torque is applied to member  78 . 
         [0060]      FIG. 10  is a diagram illustrating a view of an assembled pot core inductor in accordance with one embodiment of the technology disclosed herein. In this diagram, the first and second halves of the ferromagnetic housing are shown as being disposed in an opposing configuration, and partially enclosing the wire windings of an inductive element wound around a support structure or bobbin. The adjustment mechanism, which in this embodiment is a nylon screw, is shown to the left of the assembled pot core structure and is not yet in place.  FIG. 11 , illustrates a similar pot core structure in accordance with one embodiment, but with a nylon screw in place and being adjusted by the tip of a flat blade screwdriver. 
         [0061]    While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. Likewise, the various diagrams may depict an example configuration for the invention, which is done to aid in understanding the features and functionality that can be included in the invention. The invention is not restricted to the illustrated example configurations, but the desired features can be implemented using a variety of alternative configurations. Indeed, it will be apparent to one of skill in the art how alternative configurations can be implemented to implement the desired features of the present invention. 
         [0062]    Although the invention is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations, to one or more of the other embodiments of the invention, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments. 
         [0063]    Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: adjectives such as “conventional” and “typical” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future.