WO2007042032A2

WO2007042032A2 - Electroacoustic transducer

Info

Publication number: WO2007042032A2
Application number: PCT/DK2006/000557
Authority: WO
Inventors: Lars Goller
Original assignee: Tymphany Denmark A/S
Priority date: 2005-10-07
Filing date: 2006-10-06
Publication date: 2007-04-19
Also published as: DK200501409A; WO2007042032A3

Abstract

The present invention relates to an electroacoustic transducer (30) comprising a diaphragm (34) which is connected to a basket (38) by a surround (36), where a voice coil (42) is attached to the diaphragm (34), which voice coil (42) is arranged and centred in a magnet system by a spider (44), which magnet system comprises at least two parts, and where the spider (44) comprises a number of apertures (45) or recesses, which apertures (45) or recesses are arranged in the spider (42), where a first part (40) and a second part (50) of the magnet system are connected with each other through said apertures (45) or recesses.

Description

Electroacoustic transducer

Field of the Invention

The present invention relates to an electroacoustic transducer comprising a diaphragm which is connected to a basket by a surround, where a voice coil is attached to the diaphragm, which voice coil is arranged and centred in a magnet system by a spider, which magnet system comprises at least two parts.

Background of the Invention Recently, there have been increasing demands for thinner and lighter loudspeakers for example to be built into the side of a doorframe of a car or for a loudspeaker system in a flat TV or the like.

In the following, the term "axial direction" refers to the direction of movement of a diaphragm in an electroacoustic transducer. The term "lateral direction" refers to the direction perpendicular to the aforementioned axial direction. Movement of the diaphragm in the "lateral direction" should be avoided because it introduces flexing distortion.

A traditional loudspeaker comprises a number of standard parts including a basket, a diaphragm, a voice coil, a magnet system and suspension means. The magnet system comprises a number of parts that in a traditional construction comprises a magnet, a pole piece, a top-plate and a back-plate. The pole piece and the back-plate are in some designs integrated in the same part, and the part is often referred to as a T-yoke.

The suspension means comprises a surround and a spider. The spider and surround act as a kind of spring and exhibit self-damping properties. The spider must prevent any lateral motion, which means that the spider must prevent any motion perpendicular to the preferred direction of the diaphragm that might allow the voice coil and pole piece to touch, which would destroy the loudspeaker. Furthermore, lateral movements introduce distortion known as flexing which is to be avoided in order to achieve a satisfac- toiy sound quality. The spider is usually a circular piece of fabric, which is generally made of cotton, poly-cotton blend or the like. The spider comprises a hole in the middle for connection with a voice coil. Furthermore, the spider often has multiple pleats in order to obtain flexibility.

One of the problems with a traditional loudspeaker construction is the depth of the transducer, and traditional loudspeakers are, therefore, not so suitable for being built into doorframes of cars or integrated in flat TVs where the size of the loudspeaker in the axial direction has to limited.

Various inventions have been made in order to obtain a loudspeaker with a thin profile. In the Japanese document JP2001- 152063, a loudspeaker with a thin profile is disclosed which loudspeaker is suitable for various acoustic devices. The loudspeaker comprises a suspension where the outer edge of the suspension is connected to a lower plate (back-plate), and where the inner edge of the suspension is coupled at the lower end of the voice coil. The suspension is located inside the magnet system, and the diameter of the suspension is, hereby, limited to the space defined by the magnet, the back-plate and the voice coil. This limitation affects the dynamic properties of the suspension.

m the German document DE3123098, an electroacoustic transducer is disclosed where a spider provides a suspension for a voice coil. The inner edge of the spider is connected to a voice coil, and the outer edge of the spider is connected to a top-plate of a magnet system. A similar construction with a spider inside a magnet system is disclosed in US 6,222,931 that concerns a high power acoustical transducer.

The aforementioned inventions all relate to electroacoustic transducers that comprise a spider that is arranged in the air gap of the magnet system, where the air gap is defined by the magnet, the pole-piece, the back-plate and the top-plate. However, experience has shown that the diameter of the spider is very important in order to get a good sound quality with a minimum of flexing etc. Furthermore, in the aforementioned inventions, the diameter of the spider is limited by the relatively small distance between the voice coil and the magnet of the electroacoustic transducer. The limitation. on the diameter of the spider affects the dynamic properties of the electroacoustic transducer, and it has shown to be very difficult or even impossible to use the aforementioned designs in low frequency and midrange applications such as woofers, mid- range loudspeakers etc. without introduction of distortion which is highly unwanted.

Increasing the diameter of the magnet system in order to achieve an optimum diameter of the spider will not solve the problem because this would increase the weight of the transducer considerably due to the increase in the diameter of the magnet system which is highly unwanted. Furthermore, the magnetic field strength decreases considerably if the air gap is increased, and the output performance is, therefore, also af- fected.

Object of the Invention

It is, therefore, the object of the invention to provide an electroacoustic transducer with a small size in its axial direction and at the same time provide an electroacousti- cal transducer with a substantially, optimum diameter of the spider.

This object is achieved by an electroacoustic transducer as described in the preamble of claim 1 , wherein the spider comprises a number of apertures or recesses, which apertures or recesses are arranged in the spider, where a first part and a second part of the magnet system are connected with each other through said apertures or recesses.

It is, furthermore, an object of the invention to provide a spider for use in an electroacoustic transducer, which has a small size in its axial direction and, therefore, suitable for being built into a doorframe of a car or the like. This object is achieved where the spider is made of a flexible material, and where the spider comprises a number of apertures or recesses, and which apertures or recesses are arranged in the spider.

Description of the Invention

The electroacoustic transducer according to the present invention comprises a dia- phragm that is connected to a basket by a surround. A voice coil is attached to the diaphragm by a spider, which assures that the voice coil is arranged in the centre of an air gap defined by the parts of the magnet system, which comprises a pole-piece and a magnet.

The voice coil is arranged in the air gap of the magnet system, where the interaction between the magnetic field of the magnet system, and the voice coil provides the mechanism for driving the voice coil and the diaphragm and this way generate sound, in addition to centre the voice coil in the air gap of the magnet system, the spider also provides a restoring force in order to bring the diaphragm and the voice coil back to its resting position (equilibrium).

A number of apertures or recesses are arranged in the spider, where a first part and a second part of the magnet system are connected with each other through the apertures or recesses. This way, the spider is connected to the voice coil inside the magnet system and connected to the basket at the outer edge of the spider. This is a great advan- tage compared to the prior art referred to in the beginning, where the diameter of the spider is limited to the size of the magnet system and/or the distance between the magnet and the voice coil. In an embodiment of the invention, the first part is a magnet, and the second part is a pole-piece or vice versa

Furthermore, the axial size of the transducer is reduced and the diameter of the spider is not limited by the amount of space in the air gap because the spider is connected to the basket or the frame outside the magnet system. This way, the diameter of the spider can be considerably larger than the diameter of the magnet system. The dynamical performance of the loudspeaker is hereby improved, and the rate of distortion is re- duced considerably compared to prior art where the entire spider is installed inside the magnet system. It is now possible to obtain a substantially optimum diameter of the spider with respect of sound quality and dynamical performance and at the same time reduce the axial size of the transducer by connecting the spider and the voice coil inside the magnet system.

The invention is especially suitable for woofers and midrange loudspeakers where the displacement of the spider, the voice coil and the diaphragm can be relatively large in order to generate a given sound pressure. By using the present invention, it is possible to implement woofers and midrange loudspeakers with a relatively small size in the axial direction and at the same time eliminate and/or reduce the distortion generated by the spider. The invention is, hereby, suitable for being built into a doorframe of a car or used in flat panel TVs etc. where the size in the axial direction is very important in order to keep the size at a minimum.

The weight of the system is also held low because it is no longer necessary to increase the diameter of the magnet system in order to get space enough inside the air gap to obtain a substantially optimum diameter of the spider.

In an advantageous embodiment of the invention, the spider is connected at the end of the voice coil. This way, the voice coil is prevented from lateral displacement during operation because the voice coil is connected to the spider at one end and to the diaphragm in the other. This construction assures that the voice coil is centred in the magnet system during the axial displacement of the voice coil. This construction eliminates distortion due to flexing (lateral movement) of the diaphragm during operation.

The magnet system can be implemented in a lot of different ways. A traditional con- struction comprises a magnet, a pole piece, a top-plate and a back-plate. The pole piece and the back-plate are in some designs integrated in the same part, and the part is often referred to as a T-yoke. The magnet is in some embodiments arranged in the pole-piece; however, it is important to note that the present invention is not limited to a specific design of the magnet system.

hi an embodiment of the invention, the electroacoustic transducer comprises a spider that is arranged in a position between a top-plate and a back-plate of the magnet system.

The apertures are in a preferred embodiment of the invention symmetrically positioned in the spider that assures that the deformation is symmetrically distributed on the spider. If three apertures are arranged in the spider, the angle between them would then be 120 degrees. If four apertures are used, the angle between each aperture is 90 degrees and so on.

In an advantageous embodiment of the invention, the electroacoustic transducer com- prises at least one support-part that connects the first and the second part of the magnet system. This way, a disc or a washer can be used in order to connect the first and the second part of a magnet system.

When a support part is used to connect a first and a second part of the magnet system, the cross-section of the aperture must be larger than the cross-section of the support- part in order to prevent that the displacement causes the spider to touch the support- part which would lead to unwanted effects such as increased distortion and reduced displacement of the voice coil hence the diaphragm.

The support-part is in an embodiment of the invention made of metal such as iron. This is especially useful when the pole piece comprises a magnet. The support part can in another embodiment of the invention be made of other kinds of metals such as copper or different alloys. The support-part can also be magnetized or comprise a magnet, such as a permanent magnet or the like.

In an embodiment of the invention, the first and the second magnet part comprises a number of protrusions that are prepared for connection with a corresponding counterpart of the magnet system. The protrusion goes through the apertures or recesses in the spider in order to connect the first and the second magnet part. This way, it is not nec- essary to use a support-part in order to connect the first and the second part of the magnet system.

The invention also concerns a spider, for use in an electroacoustic transducer, such as a loudspeaker or the like, where the spider comprises a number of apertures or re- cesses, which apertures or recesses are arranged in the spider. The apertures or recesses are designed to allow connection of a first and a second magnet part. The cross- section of the apertures or recesses should allow displacement of the spider without physical contact between the spider and the magnet parts even in the greatest dis- placement of the spider. The spider of the present invention is a great improvement compared to prior art where the entire spider is either adapted for installation inside the magnet system or outside the magnet system. By using the present invention, a part of the spider is arranged inside the magnet system, and a part is located outside the magnet system, and the diameter of the spider is, therefore, not limited by the size of ^• the air gap. At the same time the axial size of the electroacoustic transducer is minimized.

The outer edge of the spider is prepared for connection with a basket or a frame of the electroacoustic transducer, and the inner edge of the spider is prepared for connection with a voice coil of the electroacoustic transducer. The spider is in an advantageous embodiment of the invention connected to the end of the voice coil which end is opposite the end in the contact diaphragm. This ensures the stability of the voice coil and prevents contact between the voice coil and the pole-piece. The connection at the end of the voice coil also prevents any lateral motion that causes distortion in the generated sound.

The spider is in an embodiment of the invention a circular piece of fabric with multiple pleats which provide the necessary flexibility of the spider. Spiders are generally made of cotton, poly-cotton blend, or the like

Description of the Drawing

The invention is described in more detail with reference to the drawings, where

fig. 1 shows a cross-section of an electroacoustic transducer according to prior art, fig. 2 shows a cross-section of an embodiment of an electroacoustic transducer according to the present invention, fig. 3 shows an embodiment of a spider according to the invention comprising a number of apertures, and fig. 4 shows an embodiment of a spider according to the invention comprising a number of recesses. Detailed Description of the Invention

Fig. 1 shows a cross-section of an electroacoustic transducer 2. A diaphragm 4 is connected to a frame 8 through a surround 6. The electroacoustic transducer comprises a magnet system, which comprises a magnet 10, a top plate 18, a back plate 20 and a pole piece 16. The pole piece 16 and the back plate 20 are integrated in the same part. A voice coil 12 is at one end connected to the diaphragm 4 and is at the other end connected to a spider 14 that stabilizes the voice coil 12 and keeps it in the centre of the air gap 21. The air gap 21 is defined by the parts 10, 16, 18,20 of the magnet system.

The axial direction is illustrated as 24, and the lateral direction is illustrated as 22. The lateral movements of the diaphragm are to be avoided.

Fig. 2 shows an electroacoustic transducer 30 according to the present invention. The electroacoustic transducer 30 comprises a diaphragm 34, which is connected to a bas- ket 38 by a surround 36. The diaphragm 34 is connected to a voice coil 42, which is positioned in an air gap 46 of a magnet system. The magnet system comprises a magnet 40 and a pole piece 50. The pole piece and a back-plate is integrated in the same part. The magnet system, furthermore, comprises a top-plate 51, which is connected to the magnet 40.

A part of the voice coil 42 is positioned inside the magnet system by a spider 44. The outer edge of the spider is connected to the basket 38, and the inner edge is connected to the voice coil 42. The spider 44 and the voice coil 42 is connected inside the air gap 46 defined by the parts 40,50,51 of the magnet system. The magnet 40 and the pole piece 50 are connected to each other by a support-part, which support-part is positioned in the apertures 45 of the spider. A close-up 32 shows the magnet 40 that is connected to the pole-piece 50 by a support-part 52, which is positioned in the aperture 45 in the spider 44.

The aperture 45 makes it possible for the spider 44 to be connected to the voice coil 42 inside the air gap 46 and at the same time be connected to the basket 38 at the outer edge of the spider 44. The diameter of the spider 44 is, hereby, not limited by the di- ameter of the magnet system which is a great improvement compared to prior-art transducers where the entire spider is positioned inside the magnet system.

Fig. 3 shows an embodiment of a circular spider 60 according to the invention com- prising a hole 61 for a voice coil (not shown) and a number of apertures 62,64,66,68.

The spider 60 is for use in an electroacoustic transducer, which comprises a voice coil and a magnet system. The inner edge 61 of the spider 60 is prepared for connection with a voice coil (not shown). The spider 60 comprises four apertures 62,64,66,68 which are symmetrically arranged in the spider. The diameter of the apertures 62,64,66,68 should be large enough in order to avoid connection between the edges of the apertures 62,64,66,68 and the parts of the magnet system (not shown), which parts is connected through the apertures 62,64,66,68.

Fig. 4 shows an embodiment of a spider 70 according to the invention where the spi- der 70 comprises a number of recesses 72,74,76,78 in conjunction with a hole 71 which is arranged and centred in the spider 70 and prepared for connection with a voice coil (not shown). The shape and size of the recesses 72,74,76,78 are adjusted to the size of the parts in the magnetic system (not shown) in order to avoid connection with the spider 70 and the parts of a magnet system (not shown) when the spider 70 is displaced during operation.

Claims

1. An electroacoustic transducer (30) comprising a diaphragm (34) which is connected to a basket (38) by a surround (36), where a voice coil (42) is attached to the diaphragm (34), which voice coil (42) is arranged and centred in a magnet system by a spider (44), which magnet system comprises at least two parts characterized in that the spider (44) comprises a number of apertures (45) or recesses, which apertures (45) or recesses are arranged in the spider (42), where a first part (40) and a second part (50) of the magnet system are con- nected with each other through said apertures (45) or recesses.

2. An electroacoustic transducer (30) according to claim 1 characterized in that the spider (34) is arranged in a position between a top-plate (51) and a back- plate of the magnet system.

3. An electroacoustic transducer (30) according to at least one of the claims 1-2 characterized in that the apertures (45) are symmetrically positioned in the spider (34).

4. An electroacoustic transducer (30) according to at least one of the claims 1-3 characterized in that the electroacoustic transducer (30) comprises at least one support-part (52), which support-part (52) connects the first part (40) and the second part (50) of the magnet system.

5. An electroacoustic transducer (30) according to at least one of the claims 1-4 characterized in that the cross-section of the aperture (45) is larger than the cross-section of the support-part (52).

6. An electroacoustic transducer (30) according to at least one of the claims 1-5 characterized in that the support-part (52) is made of metal such as iron, copper etc.

7. An electroacoustic transducer (30) according to at least one of the claims 1-6 characterized in that the support-part (52) is magnetized.

8. A spider (44,60,70) for use in an electroacoustic transducer (30) characterized in that the spider (44,60,70) comprises a number of apertures (45, 62,64,66,68) or recesses (72,74,76,78), which apertures (45,62,64,66,68) or recesses (72,74,76,78) are arranged in the spider (44,60,70).

9. A spider (44,60,70) according to claim 8 characterized in that the outer edge (63,73) of the spider (44,60,70) is prepared for connection with a basket (38) of an electroacoustic transducer (30), and where the inner edge (61,75) of the spider (44,60,70) is prepared for connection with a voice coil (42) of an electroacoustic transducer (30).

10. A spider (44,60,70) according to claim 8 characterized in that the spider (44,60,70) comprises a number of pleats in order to increase flexibility of the spider.