Patent Application
20070183620
1. Technical Field of the Invention
This invention relates generally to electromagnetic transducers, and more specifically to voice coil configurations for them.
2. Background Art
The diaphragm assembly includes a cone or diaphragm 28 which is coupled at its outer perimeter to the frame by a flexible suspension component referred to as a surround 30. A voice coil former or bobbin 32 is coupled to the diaphragm. A flexible suspension component referred to as a spider 34 couples the bobbin (or diaphragm) to the frame. An electrically conductive voice coil 36 is wound around the bobbin and is disposed within the magnetic air gap of the motor structure. Some transducers include only a single voice coil. Some, such as that shown, include a single layer of windings. The ends of the voice coil are connected (by wires or leads not shown) to a + terminal and a − terminal, respectively. The terminals may conveniently be located at a terminal block 38.
For ease of illustration, the particular routing of the wiring from the voice coil to the terminals has been omitted from the drawings, as it is well known in the art. In various transducers, the wires are routed up the outside of the bobbin, or the inside of the bobbin, along or in the spider from the bobbin to the terminal block, or hanging in the air between the bobbin and the terminal block, or along the diaphragm, and so forth.
The system builder could, of course, wire only one of the voice coils, presenting a 4Ω load, which is only 2× the parallel configuration and ½× the series configuration. Unfortunately, with the other voice coil inactive, the efficiency of the transducer is remarkably reduced. Additionally, the inactive voice coil unnecessarily increases the moving mass, reducing the efficiency and limiting the high frequency range of the transducer as compared to a similar transducer which does not have the dead-weight coil.
Unfortunately, each dual voice coil transducer offers only two selectable full efficiency loads which are at best 4× different if the coils are the same impedance, and one or two reduced efficiency loads. What is needed, then, is an improved electromagnetic transducer which gives the system builder a significantly greater number of selectable impedances in increments significantly tighter than 4×, allowing the system builder to more closely match a desired impedance.
The invention will be understood more fully from the detailed description given below and from the accompanying drawings of embodiments of the invention which, however, should not be taken to limit the invention to the specific embodiments described, but are for explanation and understanding only.
Having three voice coils gives an increased number of options for the system builder, and the greater the number of different impedances there are among the three coils, the more options the system builder will have. Table 1 demonstrates the impedance choices available from each of six different sets of impedances for the three voice coils.
The impedances of the three voice coils can be selected in any combination suitable to achieve the transducer designer's goals. Six exemplary combinations are presented here, as “Config 1” through “Config6”. The three voice coils are identified as VC1, VC2, and VC3. There are five possible ways to wire three voice coils, using all three voice coils to maintain constant, maximum efficiency:
1) all three in parallel, shown as VC1∥VC2∥VC3
2) VC1 and VC2 in parallel, and VC3 in series with them, shown as (VC1∥VC2)—VC3
3) VC1 and VC3 in parallel, and VC2 in series with them, shown as (VC1∥VC3)—VC2
4) VC2 and VC3 in parallel, and VC1 in series with them, shown as (VC2∥VC3)—VC1
5) all three in series, shown as VC1—VC2—VC3
The “Rank” subtable sorts the five net impedances of each configuration into ascending order. The “X more than next lower” subtable indicates the increase of each of the last four impedances over the next lower one (no entry is present for the lowest impedance). The “Stdev of last 3” entry indicates the standard deviation of the last three entries in the “X more” subtable, and is a measure of the log scale linearity of the four highest impedance values for that voice coil configuration.
The all-in-parallel combination will, by the mathematical relationship of parallel impedances, in many instances, be somewhat less usef uil to the system builder than the other four, and in some cases may be ignored or considered an “outlier”. For example, consider Config 6. Its four largest impedance possibilities present the system builder a log scale nearly linear progression of choices from 0.99Ω to 3.5Ω, which are very useable in e.g. car audio applications, in which amplifiers are commonly available in skus which are stable from 1Ω to 4Ω. The all-in-parallel impedance of 0.16Ω is significantly outside this range, and is not especially useable in car audio, home audio, etc. applications.
It should be noted, however, that the system builder may wish to couple two or more transducers in series, in which case the all-in-parallel outlier may, in fact, be useful. In fact, it may be the case, depending upon the voice coil impedance values chosen, and the needs of the application at hand, that any of the combinations might be undesirable or substantially redundant.
It should be noted that, although
Having four voice coils gives an even greater number of options for the system builder. Table 2 demonstrates the impedance choices available from each of six different sets of impedances for the four voice coils. These are, of course, only exemplary values, and the designer will select values according to the needs of the transducer's target application.
Similar notation is used in Table 2, as was explained above regarding Table 1. Six exemplary combinations are presented here, as “Config 1” through “Config 6”. The four voice coils are identified as VC1, VC2, VC3, and VC4. There are fifteen possible ways to wire four voice coils, using all four voice coils to maintain constant, maximum efficiency:
1) VC1∥VC2∥VC3∥VC4
2) (VC1∥VC2∥VC3)—VC4
3) (VC1∥VC2∥VC4)—VC3
4) (VC1∥VC3∥VC4)—VC2
5) (VC2∥VC3∥VC4)—VC1
6) (VC1∥VC2)—(VC3∥VC4)
7) (VC1∥VC3)—(VC2∥VC4)
8) (VC1∥VC4)—(VC2∥VC3)
9) (VC1∥VC2)—VC3—VC4
10) (VC1∥VC3)—VC2—VC4
11) (VC1∥VC4)—VC2—VC3
12) (VC2∥VC3)—VC1—VC4
13) (VC2∥VC4)—VC1—VC3
14) (VC3∥VC4)—VC1—VC2
15) VC1—VC2—VC3—VC4
In one such embodiment, the motor structure uses a “push-push” dual gap geometry such as taught in U.S. Pat. No. 6,917,690, in which the magnetic flux flows in a same direction (e.g. radially inward) over both magnetic air gaps. In this case, the motor structure includes one or more permanent magnets 100 disposed between the back plate and the lower top plate. The motor structure includes a magnetically permeable member 102 disposed between the lower top plate and the upper top plate. The member 102 may be a permanent magnet, polarized in the same direction as the magnets 100, as taught in the '690 patent, or it may be a steel spacer, as taught in co-pending application Ser. No. 10/289,109, commonly assigned with the '690 patent and the present application.
In another such embodiment, the motor structure uses a “push-pull” geometry in which the magnetic flux flows in opposite directions over the two magnetic air gaps, that is, radially inward over one and radially outward over the other. In this case, elements 100 may be interpreted as aluminum spacers, and element 102 should be interpreted as a permanent magnet, with opposite polarity if elements 100 are permanent magnets rather than non-magnetic spacers.
In either the push-push or the push-pull configuration, the bobbin 104 has wound about it at least three voice coils of more than one impedance, and the magnetic air gaps each has disposed within it some subset of the voice coils.
The lower magnetic air gap may contain a first two-layer voice coil 106, 108 and a second two-layer voice coil 110, 112. The upper magnetic air gap may contain a third two-layer voice coil 114, 116 and a fourth two-layer voice coil 118, 120. The eight wires extending from the eight ends of these four voice coils are coupled to respective + and − terminals at a terminal block 122, and can then be connected in any of the fifteen combinations identified above in Table 2.
Alternatively, the lower magnetic air gap may contain a four layer voice coil 106, 108, 110, 112, and the upper magnetic air gap may contain both a three layer voice coil 114, 116, 118 and a single layer voice coil 120. The six wires extending from the six ends of these three voice coils are coupled to respective + and − terminals at the terminal block, and the system builder can select any of five configurations identified above in Table 1.
Alternatively, each magnetic air gap may contain four single layer voice coils, for a total of eight voice coils which can then be coupled in a very large number of series/parallel permutations.
Alternatively, one or both of the magnetic air gaps may contain less than four layers of voice coil windings. The reduced number of layers can be created using wire of larger diameter, resulting in the same voice coil outer diameter.
Alternatively, one or more voice coils (as determined by the wires available at the terminal block) may be present in both magnetic air gaps. For example, the layer 106 and the layer 114 may together comprise a single voice coil.
Additionally, more than two magnetic air gaps may be present in the motor structure, as taught in the '690 patent, and the three or more voice coils of the present invention may be distributed in them in any manner deemed appropriate by the transducer designer.
Any of a variety of fastening means can be used to secure the plug to the terminal block. For example, screws, bolts, elastic, hook-and-loop fasteners, clamps, clips, and so forth. Ideally, the plug is releasably secured to the terminal block, to enable the subsequent substitution of a different plug.
Plug 1 achieves the all-in-parallel configuration via wires or traces (hereinafter simply “wires”, for convenience) connecting the T+ terminal to each of the A+, B+, and C+ terminal connectors, and wires connecting the T− terminal to each of the A−, B−, and C− terminal connectors. The + input signal is thus applied via the A+ etc. terminal connectors to the VC1+ etc. terminal connectors and thence to the + end of each of the voice coils, and thence via the VC 1− etc. terminal connectors to the A− etc. terminal connectors, and thence to the T− terminal and back to the amplifier to complete the circuit.
Three or more voice coils are disposed in the magnetic air gaps such that each coil extends substantially from the center of one gap to the center of the other gap, as shown. Minor variance may need to be made in the winding, with each next outermost layer of windings terminating slightly short of the layer over which it is wound. The layers of windings are shown as being of identical axial length, for convenience.
In one embodiment, the transducer includes a first voice coil 142, a second voice coil 144, and a third voice coil 146. In another embodiment, it further includes a fourth voice coil 148. In some embodiments, each voice coil occupies its own, dedicated layer in the voice coil assembly.
In other embodiments, a layer may include wire windings from two or more voice coils. For example, the first and second layers 142 and 144 may include alternating first and second voice coil wires such as a bifilar configuration simultaneously wound down the bobbin (layer 142) then back up the bobbin (layer 144) over the first layer; and the third and fourth layers 146 and 148 may include alternating third and fourth voice coil wires simultaneously wound down the bobbin (layer 146) and then back up the bobbin (layer 148).
The transducer includes a terminal block 140 to which the ends of each voice coil are connected. By plugging in the right terminal block interface unit (not shown), the system builder can configure the transducer to have the desired impedance.
When one component is said to be “adjacent” another component, it should not be interpreted to mean that there is absolutely nothing between the two components, only that they are in the order indicated.
In its most simplistic configuration, a terminal connector may simply be the end of the voice coil wire, and the series/parallel connection is accomplished by joining wire ends together, e.g. by soldering them, or by fastening them with wire nuts, or the like.
The term “series/parallel” is meant to include any of the possible permutations of voice coil connections, and should not be construed as requiring both a series connection and a parallel connection.
In some embodiments, it may be acceptable to have e.g. four voice coils, with the connector plugs selecting series/parallel combinations of three or four of the voice coils. If some small number of the voice coils is unused in a configuration, the efficiency of the transducer is reduced. On the other hand, it will produce a different set of Thiele-Small small parameters (Qts will change) allowing for an alternate box tuning or different frequency response in a given box.
One significant aspect of some embodiments of this invention is that, once the appropriate terminal block interface plug has been connected, the electromagnetic transducer has only a single pair of terminals which the installer needs to connect.
The various features illustrated in the figures may be combined in many ways, and should not be interpreted as though limited to the specific embodiments in which they were explained and shown.
Those skilled in the art, having the benefit of this disclosure, will appreciate that many other variations from the foregoing description and drawings may be made within the scope of the present invention. Indeed, the invention is not limited to the details described above. Rather, it is the following claims including any amendments thereto that define the scope of the invention.
