WO2005086531A1

WO2005086531A1 - Loudspeaker

Info

Publication number: WO2005086531A1
Application number: PCT/FI2005/000092
Authority: WO
Inventors: Ilkka Turunen; Sami PENTTILÄ
Original assignee: Oy North Wave Ltd
Priority date: 2004-03-05
Filing date: 2005-02-14
Publication date: 2005-09-15
Also published as: FI20040363A0; FI20040363A

Abstract

The invention relates to a loudspeaker, particularly a so-called planar loudspeaker, the vibrating diaphragm (6) of which is essentially planar and is attached by its edges to the body of the loudspeaker, and in which there is a voice coil (3) and a magnet (5). The coil (3) attached to the body (2) is fixed and the magnet (5) is attached to the diaphragm (6) in order to move with it. The coil body (2) is permanently connected to the thermally conductive body structure (1).

Description

Loudspeaker

The present invention relates to a loudspeaker, more specifically particularly to a so-called planar loudspeaker.

Conventional loudspeaker solutions are such, in which a cone manufactured from stiff cardboard or similar acts as the diaphragm of the loudspeaker element. The cone is attached flexibly by its outer edges to the body of the loudspeaker, while in the centre of the cone, at the foot of the cone there is a voice coil, which moves in an magnetic field. Solutions are known, which the cone is manufactured from a material other than cardboard.

A second known solution is disclosed, for example, in US patent publication 3,509,290, which uses a planar diaphragm attached to the edges of the loudspeaker enclosure. The manufacturing material of the diaphragm is expanded polystyrene. According to the solution, the loudspeaker includes several different kinds of baffles, which are used to achieve sounds of difference pitches. A drawback is a quite complicated construction, which brings the additional drawback of distortion appearing, due to the mutual mixing of the sounds.

A loudspeaker solution is known from Finnish patent 94203, which is intended to improve the output/efficiency ratio of a loudspeaker and to reduce distortion. In the loudspeaker structure, there is a planar diaphragm, which is attached by its edges to the loudspeaker enclosure. The diaphragm is equipped with a baffle in its central area, so that the diaphragm is more resilient, for example, thinner, near to the baffle, than in the area farther away. There is still room for improvement in the efficiency of the solution and in the formation of distortion.

An additional drawback in many loudspeaker solutions in that heat is created in the sound-formation process, and is difficult to remove. The rise in temperature reduces the effective efficiency. The present invention is intended to avoid the drawbacks of the solutions according to the prior art, and to create a loudspeaker which is more efficient than known loudspeakers. In particular, the intention is to create a construction, in which the removal of the heat from the coil is especially effective.

The aforementioned and other advantages and benefits of the present invention are achieved in the manner stated to be characteristic in the accompanying Claims.

The invention is illustrated in greater detail, with reference to the following drawings, in which:

Figure 1 shows a cross-section of the voice coil solution according to the invention in a loudspeaker; and

Figure 2 shows, in turn, a cross-section of a voice coil arrangement according to a second embodiment of the invention.

In the figures, the invention is shown only on the basis of certain general principles, which are significant in terms of the present invention. Thus, the overall construction of the loudspeaker can be as desired and is not depicted here in greater detail.

As stated, Figure 1 shows a solution according to the invention, for arranging the voice coil. The voice coil is marked with the reference number 3. The coil 3 is attached to the coil body 2, which is in turn attached by means of an attachment surface 4 to an essentially plate-like body piece 1 of a material with a high thermal conductivity.

The body 2 of the voice coil is, in the conventional manner, for example, of aluminium. In solutions according to the prior art, the removal of heat has been attempted to be taken care of only with the aid of such an aluminium coil body, with poor results. In the solution according to the invention, the coil body is made hollow, mainly, if not solely in the form of a tube with a circular cross section. Thus heat can be removed both outwards and inwards from the coil.

Heat is conducted from the coil body 2 to the surrounding air, but also through the body 1 to a wider area than is the case of only the body 2. In addition to this, the flow of air that takes place inside the coil body 2 carries the heat effectively away from the coil.

According to the invention, an essential difference with known constructions is, in this construction according to the invention, that the coil 3, and not the magnet as in many constructions according to the prior art, is now the component that remains stationary.

In Figures 1 and 2, various arrows are used to depict how the heat is removed from the construction according to the invention. Thus a solid arrow shows the heat being conducted away from the construction, an open-headed arrow shows the heat being conducted from the coil body to the body material 1 , and a double-headed arrow shows heat being moved along with an airflow. From this simple diagram, it is easy to conclude that the removal of the heat is effective.

As stated previously, an increase in the temperate of the coil increases the internal resistance of the coil, which leads to a reduction in the effective efficiency of the coil. The reduction in efficiency means that more power must be fed to the coil to compensate, which in turn leads to a further increase in temperature. This results in a treadmill situation, the correction of which demands the effective removal of heat.

Figure 2 shows a more highly developed solution than that above, which includes not only all the basic features shown in Figure 1 , but also a magnet 5 attached to the loudspeaker diaphragm. Thus, according to the invention, the work pair of the coil arrangement 2, 3, which has a tubular basic construction, is a magnet 5 arranged to move together with the diaphragm, and which is attached to the diaphragm 6. In very many conventional solutions, the magnet 5 would be stationary and the coil 3 would be attached to the diaphragm. Now the entire structure is turned the other way round.

The construction of the magnet 6 is such that it contains an annular gap 7. As can be easily concluded from Figure 2, the essentially tubular coil 3 with its body 2 is intended to enter the groove of the magnet 5, according to the direction given. The diaphragm 6 thus vibrates and moves in the manner shown by the arrow 8, which means that the air inside the coil body 2 is in a continually cooling movement, because the vibrating movement causes the structure to act as a continuous pump.

As has become quite obviously from the above, the invention brings new ideas to the thermal economy of a loudspeaker, with the aid of which the heat that naturally arises can be effectively transported away from the coil, thus achieving a clear improvement in effective efficiency.

Adaptations are possible, which remain within the scope of the protection of the basic idea of the invention and the accompanying Claims. Thus, for example, the removal of heat according to the basic idea of the invention can also be achieved using a magnet 5 that is of a type that goes inside the coil body 2, without the part that comes outside the coil body. There will nevertheless be a powerful pump effect inside the coil body. In that case, the movement of air on the outer surface of the coil body 2 will not be as strong as in the case of an annular magnet, but the total economy will nevertheless be good.

In addition, reference can be made to the fact that while the best cross-section of the coil body 2 is circular, there is nothing to prevent it being made in some other shape. It is obvious that, in the best case, the shape of the cross-section of the magnet conforms to that of the coil body, but not necessarily very closely.

Claims

1. A loudspeaker, particularly a so-called planar loudspeaker, the vibrating diaphragm (6) of which is essentially planar and is attached by its edges to the body (3) of the loudspeaker, and in which there is a voice coil (2) and a magnet (5), which is attached to the diaphragm (6) to move with it, installed in the body (2) characterized in that the body (2) of the voice coil (3) is at least partly hollow and that the magnet (5) is intended to go at least partly inside the coil body (2), in order to create a pump effect.

2. A loudspeaker according to Claim 1 , characterized in that the coil body (2) is permanently connected to the thermally conductive body structure (1 ).

3. A loudspeaker according to Claim 1 , characterized in that the coil body (2) is essentially tubular.

4. A loudspeaker according to Claim 3, characterized in that the magnet (5) is equipped with an essentially annular groove (7), for receiving the coil/coil body (2, 3).

5. A loudspeaker according to any of the above Claims, characterized in that the cross-section of the part of the magnet (5) that foes inside the coil body (2) corresponds essentially to the cross-section of the coil body (2).