Electrodynamic acoustic transducer with conductive membrane for coil connection

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Austrian Patent Application No. A50411/2017, filed on May 15, 2017, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to an electrodynamic acoustic transducer, which comprises a housing, a membrane and a coil arrangement attached to the membrane, wherein the coil arrangement comprises a plurality of coils each having two terminals being static in relation to the housing. At least one pair of coils is serially connected and has one terminal in common. The remaining terminals are individual terminals. Furthermore, the transducer comprises a magnet system being designed to generate a magnetic field transverse to a longitudinal direction of a wound wire of the coil arrangement. Finally, the transducer comprises connecting wires connecting the coils at connecting points, which are between the connecting wires and the coils, with the terminals.

An electrodynamic acoustic transducer of the kind above generally is known. In this context US 2014/321690 A1 discloses a speaker with two coils stacked above another switched in series. Accordingly, the coils have one terminal in common, and the coil arrangement is connected to three terminals by means of three connecting wires.

A drawback of prior art transducers is that the connecting wires are difficult to handle, in particular if they are very thin as this counts for micro transducers, which for example are built-in into phones and other kind of mobile devices. Accordingly, manufacturing is technically complicated and makes the transducer more expensive. In addition, connecting wires, which can be seen as springs, influence and hinder the movement of the membrane. For example, the membrane does not just move piston-like, but also rocks respectively tumbles, which is caused by undesired but unavoidable asymmetries of the speaker. Usually, the connecting wires are comparably long and often shaped like a loop so as to provide a low spring constant, thus keeping the influence of the connecting wires on the movement of the membrane low. Although said influence may be reduced in the presented way, it does not disappear.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to overcome the drawbacks of the prior art and to provide an improved electrodynamic acoustic transducer. Particularly, the influence of the connecting wires on a movement of the membrane shall be reduced in comparison to prior art transducer designs.

The inventive problem is solved by a transducer as defined in the opening paragraph, wherein a conductive layer or path attached to the membrane electrically connects the coils and the common terminal. Particularly, the conductive layer or path connects a common connecting point between the coils and the common terminal.

In this way, a dedicated connecting wire from a common connecting point between the coils to the common terminal, as it is used in prior art designs, can be omitted. Instead, a conductive layer or path on the membrane is used for this reason. Accordingly, the influence of the connecting wires on a movement of the membrane is reduced in comparison to prior art transducer designs. However, a short piece of wire may be used to connect the common connecting point between the coils with the conductive layer or path. Said wire particularly may be a section of the coil wire of one of the coils or both coils at the common connecting point. Both coils may be electrically connected directly at the conductive layer or path or at a distance of the conductive layer or path. Accordingly, in the latter case, a separate, short piece of wire, a short section of the coil wire of one of the coils or short sections of the coil wires of both coils may connect the common connecting point with the conductive layer or path.

Advantage is taken of the fact that just comparably low currents (e.g. for controlling tasks) flow out of or into the common terminal in usual applications, whereas comparably high currents (e.g. caused by an audio signal) can flow from a first coil to a second coil via the common connecting point arranged on the moving part of the speaker. In particular, the resistance of the conductive layer or path is higher than the real value of the impedance of each of the coils, which the conductive layer or path is connected to. Accordingly, the conductive layer or path can be made comparably thin thus hardly deteriorating the membrane characteristics.

In particular, the conductive layer or path may comprise or consist of a conductive adhesive, glue and/or paint attached to the membrane and/or a metallic foil attached to the membrane. Accordingly, the invention can be applied to existing designs easily by simply attaching the conductive layer or path to an existing membrane.

Generally, mounting the coils to each other may be done by means of an adhesive or glue. The coil arrangement may have the shape of a polygon (e.g. of a rectangle or a square) or may be round (e.g. oval or even circular). Moreover, the coil arrangement may comprise two or more coils. The coils of the coil arrangement can be wound in the same direction or in opposite directions.

Particularly, the coil arrangement can comprise coils (in particular two coils), which are identical in shape and which are mounted to each other head first. Using identical coils allows for manufacturing the coil arrangement in a very economic way.

Further details and advantages of an audio transducer of the disclosed kind will become apparent in the following description and the accompanying drawings.

In an advantageous embodiment of the transducer, the individual connecting points between the connecting wires and the coils and/or the common connecting points are symmetrically arranged on the coil arrangement. In this way, the influence of the connecting wires on the rocking/tumbling movement of the membrane can even be more reduced. Forces acting on the membrane caused by the connecting wires are symmetric and do not cause a rocking/tumbling movement of the membrane. So, the influence of the connecting wires on the rocking/tumbling movement of the membrane is practically zero in this case.

In particular, the individual connecting points between the connecting wires and the coils are and/or the common connecting points symmetrically arranged on the coil arrangement

a) seen in a direction perpendicular to a plane encompassed by a wound wire respectively by a wire loop and/or

b) with respect to a height extension perpendicular to a plane encompassed by a wound wire respectively by a wire loop.

In case a) the coil arrangement is viewed in the direction of a loop axis respectively in a direction, in which the wound wire appears as a loop or as loops. In this view, the individual connecting points between the connecting wires and the coils and/or the common connecting points are symmetrically arranged around the coil arrangement. This is a first approach of symmetry of the individual/common connecting points.

The “loop axis” is perpendicular to a plane encompassed by the wound wire respectively a wire loop. In other words, the loop axis is the axis, around which the coil has to be rotated to wind the coil.

In case b) the individual/common connecting points are beneficially arranged in the same plane (which is encompassed by the wound wire respectively a wire loop of the coil arrangement) and in particular in the mid of a height extension of the coil arrangement. However, the individual/common connecting points may also be arranged in different planes or at different heights to obtain symmetry. For example, a first pair of two individual/common connecting points may be arranged opposite to each other on a first height or level, whereas a second pair of two individual/common connecting points may be arranged opposite to each other on a second height or level. This case b) is a second approach of symmetry of the individual/common connecting points, which can be used alone or in combination with the first approach (case a) of symmetry.

Beneficially, individual/common connecting points may be arranged in a bonding plane of two coils. In this way, manufacturing the coil arrangement is comparably easy. In case of an even number of coils (e.g. two coils), the individual/common connecting points may be arranged in the mid of a height extension of the coil arrangement. If two identical coils are mounted to each other head first, symmetry with regards to the height extension of the coil arrangement can be obtained easily.

The advantage of a conductive layer or path attached to the membrane electrically connecting the coils and the common terminal turns out to be particularly advantageous in the context of symmetric individual connecting points. This especially counts for cases where an odd/even number of terminals is needed for a polygon-shaped coil with an even/odd number of corners/sides. An illustrative example is a rectangular or square coil arrangement with three terminals. Symmetry can be obtained with two symmetrically arranged connecting wires for two “outer” individual terminals and a conductive layer for the common terminal.

Beneficially, also the individual terminals and/or common terminals are symmetrically arranged around the coil arrangement thus further improving the performance of the transducer by avoiding rocking/tumbling of the membrane. Similar to the individual/common connecting points, also the terminals can be symmetrically arranged a) seen in a direction perpendicular to a plane encompassed by a wound wire respectively by a wire loop and/or b) with respect to a height extension perpendicular to a plane encompassed by a wound wire respectively by a wire loop.

To even further improve the performance of the transducer, the connecting wires may be symmetrically arranged around the coil arrangement and/or may be substantially identical in shape.

In yet another beneficial embodiment of the proposed transducer, multiple connecting wires connect a polygonal coil arrangement at its corners. For example, this embodiment provides perfect symmetry for rectangular coil arrangements. Alternatively or in addition, it is very advantageous, if a connection between the conductive layer or path and the coils respectively a common connection point is arranged in a corner of a polygonal coil arrangement, in particular of a rectangular coil arrangement. In view of polygonal coil designs, the magnet system often comprises a number of separate, rod-shaped magnets (respectively magnets shaped like a cuboid) instead of a single ring-shaped magnet. Accordingly, the magnetic field is concentrated on the longitudinal sides of the polygon and is relatively weak in its corners. That is the reason why an individual connection point and/or a common connection point in the corner has nearly no influence on the performance of the transducer. As said, this particularly counts for a magnet system with rod-shaped magnets, but—of course in an alleviated way—also for ring-shaped magnets. Alternatively, multiple connecting wires may connect the coil arrangement at the center of its longitudinal sides what leads to perfect symmetry as well.

Like reference numbers refer to like or equivalent parts in the several views.

DETAILED DESCRIPTION OF EMBODIMENTS

All directional references (e.g., “plus”, “minus”, “upper”, “lower”, “upward”, “downward”, “left”, “right”, “leftward”, “rightward”, “front”, “rear”, “top”, “bottom”, “over”, “under”, “above”, “below”, “vertical”, “horizontal”, “clockwise”, and “counterclockwise”) are only used for identification purposes to aid the reader's understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of the any aspect of the disclosure. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

As used herein, the phrased “configured to,” “configured for,” and similar phrases indicate that the subject device, apparatus, or system is designed and/or constructed (e.g., through appropriate hardware, software, and/or components) to fulfill one or more specific object purposes, not that the subject device, apparatus, or system is merely capable of performing the object purpose.

Joinder references (e.g., “attached”, “coupled”, “connected”, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims.

All numbers expressing measurements and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”, which particularly means a deviation of ±10% from a reference value.

FIG. 1shows an example of an electrodynamic acoustic transducer1a, which may be embodied as a loudspeaker, in cross sectional view.FIG. 2depicts a top view of the transducer1a. The transducer1acomprises a housing2and a membrane3with a bending section4and a stiffened center section5. Furthermore, the transducer1acomprises a coil arrangement6aattached to the membrane3. The coil arrangement6acomprises a first coil7and a second coil8. The first coil7is arranged on top of the second coil8and concentric to the second coil8in this example. Generally, mounting the coils7,8to each other may be done by means of an adhesive or glue.

Furthermore, the transducer1acomprises a magnet system with a magnet9, a pot plate10and a top plate11. The magnet system generates a magnetic field B transverse to a longitudinal direction of a wound wire of the coil arrangement6a.

The first coil7and the second coil8are electrically switched in series. Accordingly, the first coil7has an individual terminal T7being static in relation to the housing2. Similarly, the second coil8has an individual terminal T8being static in relation to the housing2. A connecting wire12connects the terminal T7and the first coil7at an individual connecting point C7, and a connecting wire13connects the terminal T8and the second coil8at an individual connecting point C8.

Furthermore, the first coil7and the second coil8have a common terminal T78. A conductive path14a, which is attached to the membrane3and which is electrically connected to the common connecting point C78of the coils7,8, is used for this reason.

Concretely, a short piece of wire15connects the common connecting point C78of the coils7,8and the conductive path14a. On the outer, fixed part of the membrane3respectively conductive path14a, the common terminal T78is arranged. The conductive path14amay comprise or consist of a conductive adhesive, glue and/or paint attached to the membrane3and/or a metallic foil attached to the membrane3.

The common connecting point C78is arranged directly at the moving coils7,8. Beneficially, the connection at the moving coils7,8is made with low ohmic resistance.

FIG. 3shows an alternative embodiment an electrodynamic acoustic transducer1b, which is similar to the transducer1ashown inFIGS. 1 and 2. In contrast, the conductive path14bis not attached to the upper side of the membrane3, but to the lower side. Additionally, the short piece of wire15is arranged on the outer side of the coil arrangement6b, and not on the inner side. Finally, the common terminal T78is vertically arranged on the circumference of the housing2.

FIG. 4shows a simplified circuit diagram of the coil arrangement6ashown inFIGS. 1 and 2. Concretely,FIG. 4shows a voltage source, generating the voltage UIn, which is fed to a serial connection of the first coil7and the second coil8. In common designs, the voltage UInforms a sound signal, and a current IIncaused by the voltage UIn, which flows into the terminal T7and out of the terminal T8is comparably high. In contrast, currents flowing out of or into the common terminal T78, which are used for controlling tasks for example, are comparably low. One should note that the technical teaching disclosed in the context ofFIG. 4equally applies to the transducer1bshown inFIG. 3.

By means of the conductive path14a,14bthe number of connecting wires and thus their influence on a movement of the membrane3can be reduced. The conductive path14a,14bhas nearly no influence on a rocking or tumbling tendency of the coil arrangement6a. However, to further improve symmetry, a further conductive path14cmay be arranged vis-a-vis of the first conductive path14aor14bas this is shown inFIG. 5. The further conductive path14cmay be electrically connected to the coils7,8or not. Another possibility to improve symmetry is to attach a conductive layer to the whole membrane3or to attach a conductive layer with symmetric shape to the membrane3. Further conductive paths14d,14emay be attached to the membrane3to connect further common connecting points between coils7,8, e.g. if the coil arrangement6acomprises more than two coils7,8switched in series and thus more than one common connecting point C78and more than one common terminal T78.

A further possibility to connect more than one common connecting point C78in case of more than two coils7,8switched in series is to arrange different conductive paths or layers on top of each other and/or on different sides of the membrane3. In this context,FIG. 6shows a cut out of an exemplary membrane3in cross sectional view (in particular of its bending section4). Several conductive paths or layers are attached to the membrane3, concretely a first conductive path or layer14aon the upper side of the membrane3, a second conductive path or layer14fon top of the first conductive path or layer14aand a third conductive path or layer14gon the lower side of the membrane3. The layers14a,14f,14gmay cover the whole area of the membrane3or parts thereof. Of course, the layers14a,14f,14gmay differ from each other in size and shape.

FIG. 6also shows that a layer or path14aon top of the membrane3may be connected to a wire15by means of a feedthrough or via16. On the lower side of the membrane3there is a contact pad17, which the wire15is connected to. As there is also the third conductive path or layer14gon the lower side of the membrane3, the contact pad17is insulated by means of the insulation18.

It should be noted thatFIGS. 1 to 6just illustrate the possibilities how to arrange a conductive path or layer14a. . .14gon the membrane3and how to contact it with the coil arrangement6a. . .6b. Other embodiments are imaginable without departing from the spirit of the invention. For example, the wires of the coils7,8may directly be led to the contact pad17or the conductive path or layer14a. . .14gso as to achieve the serial connection of the coils7and8. In this case, the common connecting point C78is situated on the connection pad17or the conductive path or layer14a. . .14g. Accordingly, the conductive path or layer14a. . .14g(including a via16as the case may be) forms the whole connection between the common connecting point C78and the common terminal T78, whereas in the examples before, a short piece of wire15(which generally may be a short section of a coil wire of one of the coils7,8or both coils7,8) is part of said connection. In any case, the common connecting point C78is situated on the moving part of the electrodynamic transducer1a. . .1c. Beneficially, the connection between the coils7and8via the common connecting point C78is low-ohmic, whereas the conductive path or layer14a. . .14gmay have a higher resistance. Particularly, the resistance of the conductive path or layer14a. . .14gis higher than the real value of the impedance of each of the coils7,8, which the conductive path or layer14a. . .14gis connected to. Generally, the common connecting point C78beneficially is arranged in a corner of a polygonal coil arrangement6a. . .6b(see alsoFIG. 10).

In the examples hereinbefore, the conductive paths or layers14a. . .14gare attached to the outside of the membrane3. However, this is not the only possibility. Instead, the conductive paths or layers14a. . .14gmay also be arranged within the membrane3. That means that the membrane3may have different layers, wherein some are conductive (e.g. metallic foils) and some are insulating like it is the case in a multilayer circuit board. Especially, if a high number of common connecting points C78are to be connected, the membrane3may have the acoustic function on the one hand, and the function of a circuit board (including vias16as the case may be) on the other hand.

FIGS. 7 and 8show a top view of the coil arrangement6a.FIG. 7shows an exploded view with the coils7,8displaced in diagonal direction, and FIG.8shows the coil arrangement6ain operating position with the coils7,8arranged above another.

The individual connecting points C7, C8are symmetrically arranged around the coil arrangement6a, in particular with respect to the main axes x and y of the rectangular coil arrangement6a.

In a preferred embodiment, also the terminals T7, T8are symmetrically arranged around the coil arrangement6aas is shown inFIG. 8(again with respect to the main axes x and y, respectively seen in a direction perpendicular to a plane encompassed by a wound wire respectively by a wire loop—case a). Furthermore, it is advantageous, if also the connecting wires12,13are symmetrically arranged around the coil arrangement6a(again with respect to the main axes x and y) as shown inFIG. 8. Finally, it is also advantageous, if the connecting wires12,13are substantially identical in shape as this is the case inFIG. 8.

Generally, the individual connecting points C7, C8between the connecting wires12,13and the coils7,8may be symmetrically arranged on the coil arrangement6aseen in the loop axis z respectively in a direction perpendicular to a plane encompassed by a wound wire respectively by a wire loop (case a). In this view, the wound wires of the coils7,8appear as loops. This first approach of symmetry was discussed above.

However, alternatively or in addition a second approach of symmetry of the individual connecting points C7, C8may be applied to the transducer1a. According to this approach, the individual connecting points C7, C8between the connecting wires12,13and the coils7,8are symmetrically arranged on the coil arrangement6awith respect to a height extension perpendicular to a plane encompassed by a wound wire respectively by a wire loop (case b). In particular, the individual connecting points C7, C8may be arranged in the mid of a height extension of the coil arrangement6aas this is the case inFIG. 1. The height extension of the coil arrangement6ais oriented vertically inFIG. 1. However, the individual connecting points C7, C8may also be arranged on top of the coil arrangement6aor on its bottom.

The individual connecting points C7, C8beneficially may be arranged in a bonding plane of two coils7,8, which is the case in the example shown inFIGS. 1 to 3. In this way, manufacturing the coil arrangement6ais comparably easy.

In a very advantageous embodiment, the coil arrangement6acomprises (two) coils7,8, which are identical in shape and which are mounted to each other head first. Using identical coils7,8allows for manufacturing the coil arrangement6ain a very economic way. Because the coils7,8are mounted to each other head first, symmetry with regards to the height extension of the coil arrangement6ais obtained in a very easy way.

FIG. 9now shows an embodiment of a coil arrangement6c, which is quite similar to the coil arrangement6ashown inFIG. 8. Instead, the individual connecting points C7, C8are arranged on the y-axis.

In the above examples, symmetry was disclosed with regards the individual connecting points C7, C8. Additionally or alternatively, the technical disclosure related to symmetry of individual connecting points C7, C8can also applied to the common connecting points C78. Accordingly, symmetry can be obtained for individual connecting points C7, C8and/or common connecting points C78.

FIG. 10shows a rectangular coil arrangement6dwith the individual connection points C7a, C7b, C8aand C8bin the corners of the coil arrangement6d. The connection points C7aand C8acan belong to a first serial connection of the coils7,8, whereas the connection points C7band C8bcan belong to a second serial connection of coils. Accordingly, the individual connection points C7a, C7b, C8aand C8bcan form the outer taps of two pairs of serially connected coils7,8.

In view of polygonal coil designs, often a number of separate, rod-shaped magnets9(respectively magnets9shaped like a cuboid) instead of a single ring-shaped magnet9are used. Accordingly, the magnetic field is concentrated on the longitudinal sides of the polygon and is relatively weak in its corners. That is the reason why an individual connection point C7a, C7b, C8a, C8band/or a common connection point C78in the corner has nearly no influence on the performance of the transducer1a. . .1c.

Generally, the effect of the magnetic stray field on the wires12,13,12a,13a,12b,13bis different than on the conductive paths14a. . .14ebecause of the different current levels and/or impedances. On the one hand, different current levels lead to different forces acting on the membrane3caused by the different currents flowing through the wires12,13,12a,13a,12b,13brespectively through the conductive paths14a. . .14e. On the other hand, different voltages are induced into the wires12,13,12a,13a,12b,13brespectively into the conductive paths14a. . .14ebased on their different impedances. Since the strayfield is lower in the corner regions, as said it is beneficial to use these corner regions for any of the connection types between the coils7,8and the non-moving parts of the transducer1a. . .1c, i.e. for the wires12,13,12a,13a,12b,13band/or the conductive paths14a. . .14e. Moreover, it is easier to connect the wires12,13,12a,13a,12b,13brespectively the conductive paths14a. . .14ein a region, where no magnets9are, for mechanical reasons.

FIG. 11shows a rectangular coil arrangement6e, which is quite similar to the coil arrangement6dshown inFIG. 10. In contrast, the individual connection points C7a, C7b, C8aand C8bare not arranged in the corners of the coil arrangement6e, but at the center of its longitudinal sides.

In view of the coil arrangement6dand arrangement6e, conductive paths14aand14cas shown inFIG. 5may be used for the two common connection points. However, the common connection points C78and the conductive paths14a. . .14emay also be arranged in the corners of the coil arrangement6d,6e.

InFIGS. 1 to 11, the coil arrangements6a. . .6drespectively their coils7,8are rectangular in shape. However, this is not the only possibility. A coil arrangement may also be quadratic in shape or round for example.FIG. 12shows an example of a circular coil arrangement6f. The terminals T7and T8are arranged opposite to each other inFIG. 12.

It should be noted that although the examples depicted in theFIGS. 1 to 12disclose circular and rectangular coil arrangements6a. . .6f, the invention relates to any shape of a coil arrangement6a. . .6f, in particular also to oval and polygonal shapes. Furthermore, the coils7and8may have the same height or different heights, the same diameter or different diameters as well as the same number of windings or different numbers of windings. Beneficially a coil arrangement6a. . .6fis symmetric with regards to the two main axes x and y.

It should also be noted, that the coils7,8may be wound in the same directions or in opposite directions.

Furthermore, the invention does not just relate to two coils7,8, but to any number of coils7,8.

Additionally, it should be noted that although symmetric design of individual connecting points C7, C8, C7a, C8a, C7b, C8b, common connecting points C78, terminals T7, T8, T7a, T8a, T7b, T8b, T78and connecting wires12,13,12a,13a,12b,13bis advantageous, one may also deviate from a strict symmetric design. For example, the terminals T7, T8, T7a, T8a, T7b, T8b, T78may be arranged in a different manner to provide a particular electrical interface. Furthermore, the shape of the connecting wires12,13,12a,13a,12b,13bmay be different. Nevertheless, the influence of the connecting wires12,13,12a,13a,12b,13bon the movement of the membrane3may still be substantially symmetric by choosing an adequate design.

It should be noted that the invention is not limited to the above mentioned embodiments and exemplary working examples. Further developments, modifications and combinations are also within the scope of the patent claims and are placed in the possession of the person skilled in the art from the above disclosure. Accordingly, the techniques and structures described and illustrated herein should be understood to be illustrative and exemplary, and not limiting upon the scope of the present invention. The scope of the present invention is defined by the appended claims, including known equivalents and unforeseeable equivalents at the time of filing of this application. Although numerous embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this disclosure.

LIST OF REFERENCES