Patent Grant
6934402
1. Field of the Invention
The present invention relates generally to improvements in planar-magnetic speakers. More particularly, the invention relates to magnetic circuit configurations for single-ended and double-ended devices.
2. Background
Two general fields of loudspeaker design comprise (i) dynamic, cone devices and (ii) electrostatic thin-film devices. A third, heretofore less-exploited area of acoustic reproduction technology is that of thin-film, fringe-field, planar-magnetic speakers.
This third area represents a bridging technology between these two previously recognized areas of speaker design; combining a magnetic motor of the dynamic/cone transducer with the film-type diaphragm of the electrostatic device. However, it has not heretofore produced conventional planar-magnetic speakers, which, as a group, have achieved a significant level of market acceptance over the past 40-plus years of evolution. Indeed, planar-magnetic speakers currently comprise well under 1% of the total loudspeaker market. It is a field of acoustic technology which has remained exploratory, and embodied in only a limited number of relatively high-priced commercial products over this time period.
As with market acceptance of any speaker, competitive issues are usually controlling. In addition to providing performance and quality, a truly competitive speaker must be reasonable in price, practical in size and weight, and must be robust and reliable. Assuming that two different speakers provide comparable audio output, the deciding factors in realizing a successful market penetration will usually include price, convenience, and aesthetic appearance. Price is obviously primarily a function of market factors such as cost of materials and cost of assembly, perceived desirability from the consumer's standpoint (as distinguished from actual quality and performance), demand for the product, and supply of the product. Convenience embodies considerations of adaptation of the product for how the speaker will be used, such as mobility, weight, size, and suitability for a customer-desired location of use. Finally, the aesthetic aspects of the speaker will be of consumer interest; including considerations of appeal of the design, compatibility with decor, size, and simply its appearance in relation to the surroundings at the point of sale and at the location of use. If planar-magnetic speakers can be advanced so as to compare favorably with conventional electrodynamic and electrostatic speakers in these areas of consideration, further market penetration can be possible, as reasonable consumers should adopt the product that provides the most value (bearing in mind the aforesaid factors, for example) for the purchase price paid.
A discussion of the relative successes and failures of conventional planar-magnetic speakers, and design goals and desired traits of operation will be set forth. It is interesting to note that the category of fringe-field, planar-magnetic speakers has evolved around two basic categories: single-ended; and, symmetrical double-ended designs, the latter sometimes being called “push-pull.”
A conventional double-ended, or push-pull, device is illustrated in FIG. 1. 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 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 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. Also, they have certain performance limitations stemming from the formation of cavity resonances arising from passage of sound waves through cavities or channels 16 formed by the spacing of the magnets of the magnet arrays 10,11 and the holes 15 in the substrates 14, 24. This can cause resonant peaks and band-limiting attenuation at certain frequencies or frequency ranges.
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.
As mentioned, another category of planar-magnetic speakers comprises single-ended devices. With reference to
Conventional single-ended devices have had to be quite large to work effectively; and even so, were less efficient than standard electrostatic and electro-dynamic cone-type loudspeaker designs mentioned above. Small, or even average-sized single-ended planar-magnetic devices (compared to standard sizes of conventional speakers) have not effectively participated in the loudspeaker market in the time since introduction of planar-magnetic speakers. Very large devices, generally greater than 300 square inches, have been available to the consumers in the speaker market; and these exhibit limited competitiveness. That is to say, they are on par with standard speakers in terms of acceptance, suitability for certain applications, cost, and performance. But again, prior single-ended planar-magnetic devices with such large diaphragm areas require correspondingly relatively large, expensive structures; and, such relatively large speakers can be cumbersome to place in some domestic environments. They have relatively low efficiencies as well, compared with conventional electrostatic and dynamic transducers, requiring more powerful, and hence more expensive, amplifiers to provide adequate signal strength to drive them.
At first impression, a single-ended device might appear to be simpler and cheaper to build than a double-ended design. The same amount of magnet material can be used by doubling the thickness of the magnets to correspond to the combined thickness of a double-ended array of magnets. Because magnets which are twice as thick are cheaper than twice as many magnets half as thick in a double-ended device, there should be significant savings in a single-ended configuration. Furthermore, the structural complexity is significantly less with regard to single-ended designs, further adding to expected cost savings.
However, doubling the depth of the magnets from that of most designs does not achieve the desired design goal of providing twice the magnetic energy in the gap between the diaphragm and the array of magnets using conventional ferrite magnets used in prior planar-magnetic devices. Accordingly, the expectation for lower cost and better performance in the single-ended device has not been realized. Some attempts to improve the design of single-ended planar-magnetic devices have involved the use of many, very closely spaced, magnets, to have high enough magnetic energy. Even then, however, the planar area must be very large, using even more magnets to generate enough sensitivity and acoustic output. For at least these reasons, prior attempts to develop a commercially acceptable single-ended planar-magnetic device have not achieved the desired lower-cost design goals. This is true even though the basic form of their structure would seem to be simpler than push-pull devices.
The architecture of the double-ended planar-magnetic loudspeaker is quite different from that of a single-ended design. For example, the magnetic circuits of the front and back magnetic structures interact, and require a different set of parameters, spacing, and relationships between the essential elements to be optimized, for best results. This double-ended magnetic relationship causes greater repulsion forces, making it more difficult to have a stable mechanical structure, but also gives a more focused field, which can make for better utilization of magnetic material. Very few of those interactive relationships are transferable in relation to design of single-ended transducers, which have their own unique set of optimal relationships between the essential elements involved.
As mentioned, prior planar-magnetic speakers, particularly prior art single-ended devices, have utilized rows of magnets placed closely, side by side. The magnets are oriented with alternating polarities facing the film diaphragm, which includes conductive wires or strips 18 substantially centered between the magnets. Such prior devices further illustrate that the magnet energy to be captured by the conductive strips is a shared magnetic field with lines of force arching between adjacent magnets. In such prior devices, the magnetic force is assumed to be at a maximum at a point halfway between two adjacent magnets of opposite polarity orientation and, correspondingly, centered placement of the conductive strips in the field at that location is typical. To achieve this maximized flux density at the position centered between the magnets, it has been shown that (i) not only does the total size of the system need to be increased; but, (ii) the magnet placement must be much closer together and more plentiful in a single-ended device than in a push-pull planar-magnetic transducer.
Further, in contrast with standard, dynamic cone-type speakers, thin film planar loudspeakers have a critical parameter that must be optimized for proper functionality. The parameter is film diaphragm tension. (See, for example, U.S. Pat. No. 4,803,733) Proper, consistent and long-term stable tensioning of the diaphragm in a planar device is very important to the performance of the loudspeaker. This has been a problematic area for thin-film planar devices for many years, and it is a problem in the design and manufacture of current thin-film devices. Even the most carefully adjusted device can meet short-term specification requirements, but can still have long-term problems with tension changes due to the dimensional instability of the diaphragm material and/or diaphragm mounting structure. Compounding this problem is force interaction within the magnet array structure. Due to close magnet spacing of single-ended magnetic structures, the magnetic forces generated by adjacent rows of magnets can interact and attract/repel each other to a greater or lesser degree, depending upon factors such as the inter-magnet spacing and polarity relationship of the magnets. This interaction, over time, can cause materials to deform; and can impose changes on the film tension. This can degrade the performance of the speakers over time. Electrostatic loudspeakers have critical diaphragm tension issues, but they do not have relatively large magnetic forces working to change the tension in the same way or to the same degree. Dynamic cone-type speakers have magnetics and strong related forces, but generally do not utilize tensioned diaphragms. Planar-magnetic speakers pose unique challenges with respect to long-term stability for diaphragm tensioning.
With conventional planar-magnetics an increase in magnetic energy derived by increasing the number, or the strength, or both, of the magnets in the magnetic structure further exacerbates the problem of magnetic forces interference with calibrated film tension. Per the foregoing, this is true particularly over time. These and other problems are known in the art. An example of a prior art single-sided planar-magnetic device is set forth in U.S. Pat. No. 3,919,499 to Winey.
Turning now more particularly to consideration of the magnets themselves, the selection of proper magnets for planar-magnetic speakers is an important consideration. High-energy neodymium magnets have been available for over ten years, and have been used in electrodynamic cone-type speakers. As will be appreciated, however, such speakers do not employ magnetic materials structures, and supporting structures to support the magnets; and, at the same time, maintain a tension on the diaphragm that can be influenced by deformation, which can, in turn, be caused by the magnets. Such relatively more high-energy neodymium magnets have not been effectively applied to single-ended planar-magnetic transducers over this past decade, although they have been widely available. This is true even though there has been a great need for an improved magnetic circuit to enhance speaker output and reduce size.
With current magnetic structure designs having very close side-to-side spacing, a perceived problem with high-energy magnets is that the attractive forces would appear to be too intense, to a point of not only potentially distorting the supporting structure and affecting diaphragm tension, but even affecting stability of existing magnet attachment means. For these and other reasons such high-strength magnets have not been used in commercial conventional planar-magnetic transducer design.
As mentioned, particularly with double-ended devices, cavity resonances and other distortion problems arise due to the narrow channels between magnets, radiating to the outside through holes in the support structure. Single-ended devices, particularly where the magnet spacing is close, and the cavities between the magnets is relatively deep and narrow, also have been subject to distortions, particularly at the high and low frequency portion of their performance envelope. At least in part, this is also due to the close spacing of the magnets in prior devices, with attendant band limiting attenuation and resonances arising from the geometry of the cavities and holes through the supporting structure.
Also important is the magnetic circuit configuration and its relationship to the diaphragm conductive regions. The maximization of the interaction between coil and magnetic structure is key to gaining better efficiency, and can improve response, particularly at lower frequencies. Also, thermal and dimensional stability of the diaphragm material is important to performance, particularly over a long time of product use. Likewise the incorporation of the coil in or on the diaphragm is important. If the coil conductors de-bond, develop an open circuit (for example by fatigue failure), speaker performance is compromised. With both single- and double-ended devices, other considerations apply, but these give some background as to the design challenges faced. Single-ended and double-ended devices both have drawbacks and advantages relative to each other and overall both have previously been perceived to have both advantages and disadvantages compared with conventional electrostatic and electrodynamic cone-type devices. However, both single- and double-ended planar-magnetic transducers have continued to lag behind conventional cone type and electrostatic speakers in maximizing the use of magnetic drive and finding commercial acceptance.
In summary, heretofore neither conventional double-ended or single-ended designs of planar-magnetic loudspeakers have reached a stage of development which enables them to be competitive with speakers of the first two types discussed above (dynamic and electrostatic), the latter previously having higher efficiencies and lower manufacturing costs. This lack of market success, due at least in part to the reasons set out above, has continued over a period of more than 40 years.
The invention provides a planar-magnetic transducer comprising at least one thin-film vibratable diaphragm with a first surface side and a second surface side, including an active region, said active region including a coil having at least one conductive area configured for interacting with a magnetic structure for converting an electrical input signal to a corresponding acoustic output; and, a primary magnetic structure including at least one elongated high energy magnet having an energy product of greater than 25 mega Gauss Oersteds. The magnet can be greater than 34 mGO and can comprise neodymium. The transducer further comprises a mounting support structure coupled to the primary magnetic structure and the diaphragm, to capture the diaphragm, and hold it in a predetermined state of tension. The diaphragm is also spaced at a distance from the primary magnetic structure adjacent one of the surface sides of the diaphragm. The conductive surface area includes one or more elongate conductive paths running substantially parallel with said magnets. The mounting support structure, and the multiple magnets of the magnetic structure, and the diaphragm, have coordinated compositions and are cooperatively figured and positioned in predetermined spatial relationships, wherein the configurations of the magnetic relationships provide performance and/or cost/performance ratios that are improved over the prior art single ended or double ended planar-magnetic devices.
The transducer can further comprise a secondary magnetic structure which cooperates with the primary magnetic structure and the conductive area to enhance performance. The transducer can further include virtual poles, magnets of different energy configured to maximize use of magnetic energy made available. Energy can be maximum at a central portion of the transducer and decrease with lateral distance outward from the center. The gap between the magnets and the diaphragm can be varied to accommodate diaphragm movement and maximize field interaction at the same time. The secondary magnetic structure can be carried by support structure having a more open architecture to more freely accommodate sound passage, thereby improving response, particularly at high frequencies. The magnets and supporting structure can be shaped and configured to provide flaring, or horn-shaped cross sectional inter-magnet spaces, which provides improved linearity of response at high frequencies.
Magnetic structures are disclosed that create more effective use of magnetic energy distribution within the transducer, including enhanced single-ended or Quasi-push-pull structures, asymmetrical mounted magnetic structures, ferrous magnetic return paths to enhance the magnetic energy with in the structure while using fewer magnets, and re-orientation of magnets in terms of their relation ship to the diaphragm and to each other. Other inventive features will also be appreciated with reference to the following detailed description, taken in conjunction with the accompanying drawings, which together and separately illustrate, by way of example, features of the invention.
As specific examples, some of these novel magnetic structures and formats include:
a through f are schematic crossectional views of various magnet shapes;
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the exemplary embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.
With reference to
Therefore, by organizing the magnetic force available so as to be greatest in the plane of the diaphragm 21 in the center of the transducer 10, e.g. over a central magnet 35a in the illustrated embodiment, and having less energy laterally in the outermost regions (i.e. over magnets 35d and 35e), the best use of magnetic energy is provided. This can allow the cost of the magnets to be less for a given acoustic efficiency. Or, put another way, for a given cost of total magnetic mass, this embodiment can provide greater transducer efficiency.
This center concentration of available energy approach can, of course, be used with different combinations of magnets of greater count than one, and can be distributed; for example, wherein just the outermost magnets are of less energy, or any combination of all magnets other than the central magnet 35a, can be of falling energy with lateral distance from the central-most region of the transducer. Alternatively, one can take advantage of this concept by increasing the magnetic energy over the centralized portion of diaphragm, relative to magnets over a non-centralized portion of the diaphragm in a planar-magnetic transducer.
This concept takes advantage of the fact that during its active state the vibratable diaphragm 21 exhibits more ready displacement and freedom of movement in the central region 21c than at all regions away from the central region particularly when producing high outputs at the lower frequency range of the device, where the greatest diaphragm movements are required. This is realized to be due to the mechanical advantage obtained by driving the diaphragm most forcefully in the center, where it can resist displacement the least. With this in mind, one can construct a device having closer magnet face to diaphragm gap distance 31 and create more effective magnetic coupling with less magnetic field strength laterally towards the outer portions of the transducer 10 without reaching diaphragm excursion limits.
This concept of central augmentation of magnetic field energy available for coupling by the coil conductors 27 of the conductive areas 26 of the diaphragm 21 is particularly effective when combined with the concept of using higher-energy magnets, such as those having an energy of over 25 mGO, and even about 34 mGO or more. The inventors have found that going in a contrary direction from bringing the magnets closer together to increase the shared field strength between magnets, as is done in prior devices, by spreading the magnets apart, increasing their energy, and maximizing use of local loop energies, increases in various efficiencies allows a more effective device to be constructed. Further details of this design philosophy, its implementation, and advantages obtained, can be found in co-pending U.S. patent application Ser. No. 10/055,821, which is hereby incorporated by reference for the supporting teachings of that disclosure. While dealing primarily with single-ended designs, the aforementioned design direction has applicability beyond single-ended devices, as will be appreciated with reference to this disclosure.
While
The present invention can also be viewed as a method for enhancing the operation of a single-ended planar-magnetic transducer 10 which utilizes a thin-film diaphragm 21 with a first surface side 22 and a second surface side 23 that includes a conductive region 26 comprising at least one conductor configured to carry an electric audio signal. The diaphragm is positioned and spaced from a primary magnetic structure 35 and secondary magnet structure 36 including high energy magnets, at least 35a, 35b and 35c, of greater than 25 mGO, and in another embodiment are preferably greater than 34 mGO, and composed of a material or materials including neodymium. An enhanced functionality of the transducer 10 is obtained over long term use, the calibration being maintained over that time. The calibration maintained by this method relates to (i) proper spacing 55 between the magnets 35a through 35e, (ii) magnet to diaphragm spacing 31, and (iii) proper diaphragm 21 tension over a long term. The diaphragm has an acoustomechanically active area (active area) 25 that is mobilized by forces arising to act on the conductive region to produce acoustic output when the conductive runs 27 of conductive region 26 receive and carry a varying current/power of an audio signal. The coil conductors 27 are configured to cooperate with the magnet rows to drive the diaphragm in a vibratory motion, and thereby produce an audio output which the transducer is adapted to receive in electronic form and reproduce in mechanical audio wave form in air.
An exemplary embodiment of the transducer invention of
Diaphragm:
In one embodiment openings 15b in the support structure 30b supporting the secondary magnetic structure 36 can be made large. This improves (i.e. better linearizes) high-frequency response, as it opens up one side of the transducer to allow less constricted passage of sound waves, decreasing cavity resonances and high frequency attenuation. This advantage of a single-ended device is obtained in a quasi-double-ended device.
With reference to
With reference to
Turning now to
The planar-magnetic transducer 10 of
In the exemplary planar-magnetic transducer 10 embodiment of
With reference to
With reference to
The transducer 10 embodiment illustrated in
In all of the embodiments utilizing the magnet spacers 44s or 45s these spacers can be ferrous or non-ferrous and they may also be a separate spacer or may be functionally satisfied by being a formed part of support structure 30a or 30b that serves the same function as the spacer shown. Again, using a ferrous metal provides a flux return path in alternating pole magnet row configurations and can give an additional advantage in useable magnetic field energy.
In another embodiment, which can be configured as shown in
As can be appreciated from the embodiments discussed above and seen in the above-discussed drawing figures, the approach of providing a secondary magnetic structure with a magnetic field strength which varies laterally from a central portion can be accomplished a number of ways, some of which are, i) using high energy, neodymium magnets in the central portion and lower energy magnets, such as ferrite magnets, at the outer regions; ii) using larger and/or deeper high energy magnets in the central region while using smaller and/or shallower magnets in the outer regions, with those in the outer region spaced closer to the diaphragm 21; iii) using a lower number of magnet rows, and grouping them more centrally in the secondary magnetic structure, as compared with the primary structure, or some combination of the approaches.
The outer magnets may themselves be of smaller size, and/or of lower total energy capability than the central magnets but by moving them closer to the diaphragm they may produce the same, or more, or less, magnetic field strength in the actual plane of the diaphragm where the conductive strips 27 of the coil are located, than the central magnets of greater total field strength.
Alternatively, although the economical gains may not be as advantageous, more elongated conductive runs 27 i.e. coil “turns” could be placed on or in the diaphragm near the central row(s) of magnets and fewer conductive runs could be placed near the laterally outer-most magnet rows to create greater forces in the center and lower forces towards the outside. This approach can be combined with the foregoing concepts in varying the force available to move the diaphragm with position across the diaphragm.
Also, it should be clear that the magnetic distribution of greater magnetic strength in the central magnets compared to the outer magnets could be due to magnet count, magnet mass, magnet/diaphragm gap distance, or other constructs that are known in the art to affect magnetic strength in a magnetic circuit.
Moreover, while the concept has been discussed in connection with cross-sectional figures, in terms of a single transverse plane, in another embodiment the magnet strength can be varied in a transverse plane. That is to says, moving along the magnet rows in and out of the planes of the figures discussed above, the magnet energy, magnet face-to-diaphragm gap, inter-magnet spacing, etc. can be varied as well, so that looking at a speaker from the front the magnetic field set up by the magnetic structure varies with distance from the center of the diaphragm both in a vertical and a horizontal direction.
To reiterate, increasing magnetic energy in the central area or region and decreasing gap distance between the magnets and the diaphragm 21 at the outer vibratable diaphragm 21 areas or regions can provide the most acoustical efficiency with the least amount of magnetic expenditure and/or provide performance levels virtually unachievable with an equal magnetic energies all across the transducer. Again, the potential reachable with this concept utilizing high energy magnets, for example of greater than 25 mGO and even preferably greater than 34 mGO, such as is achievable in using neodymium magnets for at least a central portion of these transducers, is found to be superior than that of prior single-ended planar-magnetic transducers.
With reference to
Turning now to
With reference to
This
With reference now to
With reference now to
With reference to
With reference to
With respect to all the embodiments the configuration of the holes 15 can be varied also. The holes can be round, elongated and rounded at the ends, ovals, rectilinear, or another shape complimenting the other aspects of the particular embodiment. It has been found that using higher-strength magnets (e.g. >25 mGO) in combination with maximizing local loop interaction and opening up the inter-magnet spacing gives improved performance enabling commercially competitive devices, and the configuration of the magnets, support structure, and the openings therein, can be further manipulated to enhance performance in addition to the other improvements disclosed herein. As discussed, variation of gap spacing, inter-magnet spacing, magnet energy, coil conductor placement, and other parameters, such as size and tension of the diaphragm, for example, in combination with these novel constructions enable performance and sizes of transducers heretofore not deemed achievable for practical implementation of planar-magnetic technology.
It is evident that those skilled in the art may now make numerous other 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 not limited to the examples given herein, as it is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention and the appended claims are intended to cover such modifications and arrangements. Thus, while the present invention has been shown in the drawings and fully described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred embodiment(s) of the invention, no limitation of the scope of the invention is intended.
This application is based on, and claims priority of U.S. Provisional Application Ser. No. 60/264,474 filed Jan. 26, 2001.
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