EP2003927A1

EP2003927A1 - A diaphragm for an electrodynamic transducer

Info

Publication number: EP2003927A1
Application number: EP07109967A
Authority: EP
Inventors: Ole Wolff
Original assignee: Ole Wolff Elektronik AS
Current assignee: Ole Wolff Elektronik AS
Priority date: 2007-06-11
Filing date: 2007-06-11
Publication date: 2008-12-17

Abstract

The diaphragm (14) has a coil (16) of electrically conducting wire secured thereto and a stabilising member (21) is provided for preventing deformation of the coil. The coil (16) can have a rectangular cross section with four substantially flat portions (17, 18, 19, 20) with the stabilising member provided at the substantially flat portion to prevent deformation. The stabilising member (21) can be provided at a transition zone (22) between the coil (16) and the diaphragm (14) and can be a disc or a ring arranged within the coil (16). The stabilising member (21) can be a disc within the coil (16) with the disc and a central portion of the diaphragm (14) in an overlaying arrangement.

Description

FIELD OF THE INVENTION

This invention relates to electrodynamic transducers and in particular to electroacoustic transducers for use as speaker transducers in mobile telephones and other personal audio equipment.

BACKGROUND OF THE INVENTION

Traditionally, electrodynamic transducers such as speaker transducers and microphones have a diaphragm carrying a coil with a circular cross section and a magnetic system defining an annular air gap with a radially oriented magnetic field in the air gap and the coil arranged in the air gap. Due to the curvature of circular coils such coils are relatively rigid and therefore have a relative stable shape. However, in a ring-shaped air gap the magnetic field strength varies with the radial position in the air gap and great care must therefore be taken when mounting the coil in the air gap to ensure that the coil is properly centred coaxially in the air gap. Transducers having non-circular air gaps e.g. with linear portions have a more homogeneous magnetic field and are less sensitive to having the corresponding linear or flat portions of the coil placed at a particular position in the magnetic field. However, linear or flat portions of the coil are mechanically less stable than circular coils.
The present invention presents a solution to this problem.

SUMMARY OF THE INVENTION

The present invention solves this problem by having a stabilising member for preventing deformation of the coil. A stabilising member may be applied to any coil including circular coils and coils having one or more substantially flat portions for use in a transducer with a correspondingly shaped air gap. Advantageously, the stabilising member is provided at a transition zone between the coil and the diaphragm to provide sufficient rigidity to the coil. The stabilising member can be a disc or a ring arranged within the coil. A disc-shaped stabilising member has the advantage that it can be arranged within the coil with the disc and a central portion of the diaphragm in an overlaying arrangement. Usually, the central portion of the diaphragm is dome shaped to impart rigidity to the central portion, while the peripheral portion must be as flexible as possible. With a disc-shaped stabilising member arranged within the coil the diaphragm can be chosen primarily for its flexible properties while the disc-shaped stabilising member acts as a piston.

BRIEF DESCRIPRTION OF THE DRAWINGS

Figure 1 is an axial cross sectional view of a transducer having a diaphragm according to the invention taken along the line I-I in figure 2, and
Figure 2 is a plan view of the coil of the transducer in figure 1 taken along the line II-II.

DETAILED DESCRIPTION OF THE INVENTION

In figure 1 is shown a transducer according to the invention. The transducer has a magnetic system with a disc-shaped magnet 10 magnetised as shown in the vertical direction of the drawing. A disc 11 with a generally rectangular contour in the plane perpendicular to the figure is placed on top of the magnet, and the magnet and rectangular disc are placed inside a shallow cup 12. The rectangular disc and the cup are both made of a magnetically soft material such as iron. The side edges of the rectangular disc and the vertical sides of the cup define a rectangular air gap 13. Together with the magnet 10 the rectangular disc 11 and the cup 12 form a magnetic circuit with a magnetic field in the air gap 13. A diaphragm 14 is secured at its outer periphery to a structure 15 in solid connection to the magnetic system. The diaphragm carries a coil 16 arranged in the air gap 13.
In figure 2 is shown the coil 16 in figure 1. The coil has a rectangular cross section with four substantially flat portions 17, 18, 19, 20, i.e. portions with essentially no curvature. Only the four corners are rounded. Such substantially flat portions with essentially no curvature tend to be unstable in shape and will easily bend, and therefore a stabilising member 21 is provided for preventing deformation of the coil. In the shown embodiment the stabilising member 21 is a rectangular disc which is shown in figures 1 and 2, but a rectangular, open frame with similar outer contour can also be used. The stabilising member 21 is provided at a transition zone 22 between the coil and the diaphragm so that at least the substantially flat portions of the coil are mechanically stabilised. The diaphragm 14 overlays the stabilising member 21 and the stabilising member may be secured to the coil 16 and the diaphragm 14 by any suitable method, such as gluing or welding, at the entire contacting surfaces or just at a peripheral zone of the stabilising member. The disc-shaped stabilising member hereby also stabilises the portion of the diaphragm within the coil and acts like a rigid piston.
The corners of the stabilising member 21 may be cut as shown to leave the corners of the coil 16 without contact with the stabilising member, or the stabilising member 21 may conform to and be in contact with the entire inner periphery of the coil 16.

Claims

A diaphragm (14) for an electrodynamic transducer, the diaphragm (14) having a coil (16) of electrically conducting wire secured thereto,
characterized in that a stabilising member (21) is provided for preventing deformation of the coil (16).
A diaphragm (14) according to claim 1 wherein coil (16) has a substantially flat portion (17, 18, 19, 20), the stabilising member (21) being provided at the substantially flat portion (17, 18, 19, 20) to prevent deformation of the substantially flat portion (17, 18, 19, 20).
A diaphragm (14) according to claim 2 wherein the coil (16) has a rectangular cross section with four substantially flat portions (17, 18, 19, 20).
A diaphragm (14) according to any one of the preceding claims wherein the stabilising member (21) is provided at a transition zone (22) between the coil (16) and the diaphragm (14).
A diaphragm (14) according to claim 4 wherein the stabilising member (21) is a disc or a ring arranged within the coil (16).
A diaphragm (14) according to claim 4 wherein the stabilising member (21) is a disc arranged within the coil (16) with the disc (21) and a central portion of the diaphragm (14) in an overlaying arrangement.
An electrodynamic transducer having a diaphragm (14) according to any one of claims 1-6.