HK1058739A - Compact high performance speaker - Google Patents

Description

High-performance compact loudspeaker

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to provisional application No. 60/214,689, filed on 27/6/2000 and claims priority according to the provisions of chapter 35, article (e) of the american code. This provisional application is incorporated herein by reference in its entirety. Background

The present invention relates to an audio speaker, and more particularly, to a compact loudspeaker. In recent years, the number of applications for compact speakers has increased dramatically. This is due in part to the advent of a number of new consumer electronics and personal music electronic playback devices that require and facilitate the use of auxiliary speakers to output high quality sound at maximum volume. The trend towards small bookshelf or desk top systems has also promoted the use of compact loudspeakers, and sound effect products that have been the benchmark for many years, such as large loudspeakers operating in a box, have gradually been eliminated.

For many of these applications, lightweight and portability are of paramount importance. For some, price is a key factor. For others, it is desirable to optimize speaker performance with a box-type working or other enclosure. In this case, the structural and acoustic characteristics of the speaker and the enclosure need to be carefully considered. However, small loudspeakers pose many technical problems, especially at the low frequency end of the spectrum, because small membranes are not efficient at low frequency emissions and have high intrinsic resonances. A complete set of compensation methods will be employed to achieve the desired performance for small-scale systems, such as the use of high drive currents, longer pitch coil structures (throw coii constractions), more powerful magnetic gaps, improved thin film materials, and new cabinet structures.

It is therefore desirable to provide an improved compact loudspeaker.

It is also desirable to provide a housing which may allow the performance of a compact loudspeaker to be further improved.

It would also be desirable to provide such a speaker and enclosure design wherein the enclosure itself is adapted to be placed as a unit in a cabinet, wall or other location and which is adaptable to the mounting structure without requiring significant acoustic engineering or separate design considerations.

Disclosure of Invention

One or more of the other desirable objects are achieved by the loudspeaker of the present invention in which first and second ring magnets are collectively disposed and connected by a shunt structure at one end and a limit structure at the other end to concentrate magnetic flux in a cylindrical gap. Like the magnets, the shunt and pole piece structures are also annular and stacked on top of each other so that the combined magnetic component has an opening through the center. The voice coil of the speaker floats in the cylindrical magnetic gap, and its driving wire is connected to the rear of the speaker through the central opening. In various embodiments, the speaker membrane is connected to the tuned enclosure behind the speaker through a central opening, which further controls the overall sound effect.

According to one aspect of the invention, a cylindrical magnetic gap between two magnets separates axially polarized and oppositely polarized ring magnets. On the top of each magnet there are two t-shaped pole pieces which define a shallow voice coil gap with high flux density which is primarily connected to the magnetic gap. This configuration can be used for components using two annular neodymium magnets with outer diameters of 25 mm and 36 mm to achieve a total flux density in excess of 1.4 Tesla (Tesla) per inch of voice coil gap, and a total speaker weight of less than 2 ounces (outlce) and a total energy in the gap of 100 milliwatts (milliwatt) seconds. This reduces the mass of expensive neodymium, while effectively concentrating the effective flux in the gap and improving the overall performance of the speaker. In particular, the magnets gain high energy in a very shallow gap, which allows the membrane to be driven strongly with small amplitudes. The central through hole serves as a guide for the mounting and dismounting of the loudspeaker component and the subsequent mounting of the loudspeaker. The openings can also be used to achieve an effective level of damping or resonant coupling in a relatively shallow vessel. The container may be a door-mounted enclosure mounted on a flush or lower panel or wall.

Drawings

Illustrative embodiments and related examples of the invention are described below with reference to the accompanying drawings.

FIG. 1 illustrates a high performance magnet structure for a loudspeaker voice coil according to the present invention;

FIG. 1A illustrates another embodiment of the present invention;

FIG. 2 illustrates field vectors of the magnetic structure of FIG. 1A;

FIG. 3 is a magnetic flux density plot of the gap of the structure of FIG. 1A;

FIGS. 4A and 4B are magnetic flux paths and field lines, respectively, of the structure of FIG. 1A;

FIGS. 5-8 correspond to FIGS. 1A, 2, 3 and 4A, respectively, and illustrate features of a fixed disk magnet configuration of a first comparative configuration;

FIGS. 9-12A, 12B correspond to FIGS. 1A, 2, 3, 4A and 4B, respectively, and illustrate features of a fixed disk magnet configuration of a second comparative configuration; and

fig. 13-16A, 16B correspond to fig. 1A, 2, 3, 4A and 4B, respectively, and illustrate features of the fixed disk magnet structure of the third comparative configuration.

Detailed Description

The present invention seeks to provide an improved high efficiency loudspeaker in which the magnetic substructure is made of inexpensive metal parts. Permanent magnets are commonly used in loudspeakers, and rare earth magnets such as neodymium magnets are preferred in smaller, high performance loudspeakers. The magnetic substructure also includes shunt and pole piece structures to concentrate the magnetic field in a high flux gap where a cylindrical voice coil attached to the speaker membrane moves under the influence of an applied drive current signal.

In the design process of this loudspeaker, it is possible to seek an optimum design for the magnetic performance of the new loudspeaker, starting from the existing design, according to one of the parameters considered to be most important, such as flux, weight, physical depth or price. While this approach is straightforward, it does not effectively improve and may degrade the performance of other parameters that are not optimized. The invention provides an innovative construction that can simultaneously improve the performance of several parameters to achieve a very compact and efficient loudspeaker.

The applicant's earlier patents and patent applications are incorporated herein by reference, specifically as follows: U.S. patent application No. 5,802191, U.S. application Ser. No. 09/100,411, U.S. application Ser. No. 09/439,416, corresponding International patent application PCT/US99/27011, U.S. application No. 09/639,416, and corresponding International patent application PCT/US 00/22119. The above patents and patent applications are incorporated herein by reference in their entirety.

Fig. 1 shows an embodiment of a loudspeaker 10 according to the invention. A schematic diagram of the magnet structure 20, and the membrane D and voice coil VC are shown in detail. For example, the voice coil VC may be formed by winding copper or other conductor around a cylindrical bobbin (e.g., formed from a thin polyimide (Kapton) sheet), floating in the magnetic gap G in which the magnet structure 20 concentrates the magnetic flux. The membrane D is shown as a flat plate spanning the cylindrical voice coil VC. The outer edges of such membranes are typically suspended by flexible rubber or polymer tape to form a frame (not shown). However, in other embodiments, a convex or concave membrane spanning the diameter of the voice coil, or a flat or conical membrane extending primarily outside the circumference of the voice coil, may be used for mounting in a larger frame. In this case, a flexible but rigid in-plane annular band is attached to the voice coil or the diaphragm to keep the voice coil centered in the magnetic gap G. Another flexible strip attaches the membrane to the speaker frame, usually at the outer edge of the cone.

As shown in fig. 1, the magnet structure 20 of the loudspeaker component 10 comprises first and second ring-shaped magnets 1, 2 which are axially positioned and connected by a shunt member 3 on one side of the magnets. In the illustrated embodiment, the splitter member 3 is not a flat plate or sheet but a shaped member and tapers toward its inner and outer diameter edges. This forms ramps (or circles) 3a and 3b which extend to the thinnest area away from the central portion. On the other side of the magnets 1, 2 are formed pole pieces 4, 5, respectively. As shown in fig. 1, the inner and outer cylindrical magnets 1, 2 are closely positioned together with only a small gap between the outer circumference of the inner magnet and the inner wall of the outer magnet. The pole pieces 4, 5 each have an annular ring and are located on top of the corresponding magnet with the spacing between their facing surfaces forming the voice coil gap G. In the illustrated embodiment, the gap G is smaller than and concentric with the gap between the two magnets below. To scale, in one embodiment of the invention, the voice coil C is about 1 inch in diameter, and the inner magnet 1 has an outer diameter of 24.5 mm and a central opening of 8 mm. The magnet 2 has an inner diameter spaced 1.5 mm from the magnet 1 and an outer diameter of 36 mm. The pole pieces 4, 5 reduce the magnetic gap so that the gap G is only 1 mm. Similar to the permanent magnet 3, the pole pieces 4, 5 are thicker near the gap G and taper or taper towards their inner and outer radial edges.

Fig. 1A shows the magnet structure of a prototype of a loudspeaker according to the invention, showing a radially sectioned face of one side of the loudspeaker magnet. In this embodiment, the outer pole piece 5 has a protruding truncated cone 5 a. The edge of the film (a flat film as shown in fig. 1) may be attached to the circular table 5 a. The pole piece is formed of a suitable material, such as iron or steel, and is shaped to better utilize the magnetic flux, to concentrate it in the voice coil gap, and to provide a relief or gap so that the diaphragm does not buzz.

Fig. 3 plots the resulting magnetic flux density in the gap. As shown, the configuration of two concentric ring magnets produced a flux density of 1.4 Tesla (Tesla) through a 2 mm by 1 mm gap; the total gap energy is 100 milliwatts (milliwatt) seconds.

Fig. 2 shows vectors of the magnet structure of fig. 1A. The solid lines inserted on the right hand side of the figure represent the metal/magnet parts, where the numbers correspond to those in fig. 1. The magnets are polarized by N-S along the ring axis, and the outer ring row magnets 2 and the inner magnets are polarized in opposite directions. In this embodiment the outer pole piece 5 has at its outer circumference an extended stub or an extended band 5a, which affects the outer field lines, as will be shown in more detail in the subsequent figures. The pole piece and shunt structure on the oppositely polarized ring magnet can more effectively use magnetic substance to concentrate high magnetic flux density in the gap G.

As further shown in fig. 1, the inner magnet 1 and the permanent magnet 3 and the inner pole piece 4 are annular members defining a physical opening C in the center of the magnet assembly. Speaker input leads a, b extend through this central opening and are connected to the voice coil VC. It should be noted that the representation of the input drive lines is merely a schematic drawing. One wire is threaded through the opening and the second wire is connected to the metal structure of the speaker for grounding. Furthermore, the wires a, b need not be the wires shown, but may be in other forms, such as flexible cables or micro-lithographic conductor elements, in which plastic sheets may be embedded to reinforce the metal conductors. In addition, the drive lines may be connected from the voice coil to the surface-connected land structures on the membrane D before being connected to the conductors passing through the central aperture C. Other connection techniques in this area of technology may also be used.

However, the drive lines or leads preferably pass directly through the openings. This configuration eliminates the step of connecting the voice coil leads to a terminal plate or land located on the membrane or structural center support (cone). This is a time consuming step in the prior art, since this intermediate connection requires elaborate handling of the loudspeaker inner frame.

The opening C also allows air communication between the front and back of the speaker. Thus, when the film D extends over the entire cross-section of the magnet assembly, its performance will be affected by the stiffness of the air column that passes through the opening into the housing or other space behind the magnet. This opening may reduce the effect of the stiffness of the housing and/or direct sound from the interior of the housing when the diaphragm extends from the voice coil to its outer circumference and does not have a cover or dome in the center. Thus, the magnet openings provide acoustic coupling to match the system response and the enclosure has ports to mitigate the effects of air column stiffness in small enclosures.

Fig. 4A and 4B depict the magnetic flux paths/field lines of the ring magnet structure and the gap regions of the device of fig. 1A, each having a continuous tone and separate lines. This demonstrates that it is very effective to use small magnets in a magnet assembly with an opening to define a symmetrical flux path.

In the prototype embodiment, the double ring structure had a central opening of 8 mm for air communication and wiring. The inner neodymium ring has an outer diameter of 24.5 mm and a radial thickness of 8.25 mm, while the outer neodymium ring has an outer diameter of 36 mm and a radial thickness of 4.25 mm, so that the spacing between the two concentric magnets is 1.5 mm. Both magnets were 3.5 mm thick, so many magnetic materials equivalent to (1.47+1.45) cc or 2.97cc, weighing 22.5 grams, were used. The steel inner and outer roof panels weigh 5 and 5.77 grams (grams), respectively. The total system weight is 48 grams (grams) and provides a flux density of 1.4 Tesla (Tesla) and a total energy of 100 milliwatts (milliwatt) seconds.Comparative example 1

The value of these performance characteristics can be appreciated with reference to fig. 5-8, and by comparison with fig. 1A, 2, 3, and 4A, respectively. The total weight of the first comparative configuration was unchanged, but the system was optimized using a single hard neodymium disc magnet. As shown, the energy is much lower than in the system of the present invention, and the flux distribution in the central region of the die is essentially wasted without increasing the gap density. The total energy in the gap was 65 milliwatt (milliwatt) seconds and the total flux was 1.21 Tesla (Tesla), a total system weight of 49.5 grams (grams), and an outer shell layer in the system forms a substantial portion. Thus, of the parameters discussed above, there is only one improvement, namely a simpler core and pole piece construction in the magnet, which reduces cost.Comparative example 2

Another valuable comparison is a magnet configuration as shown in fig. 9, in which the same amount of neodymium magnet is used as in the system of fig. 1-4. In this example, the magnet is a 10 mm thick tall disk having a diameter of 24.5 mm and a weight of 12.55 grams. The top and bottom plates were the same as the previous example, but with thicker splitters, increasing the total system weight to 48.5 grams. The flux only increases to 1.32 Tesla (Tesla), but the magnet depth increases to 15.5 mm, making the structure somewhat unsuitable for shallower enclosures. Fig. 10-12B show the magnetic flux density, magnetic flux distribution, field line model, and overall geometry of the present example.Comparative example 3

If it is desired to have the same gap energy as the system of fig. 1-5 in the case of a disc magnet, the configuration shown in fig. 13 can be used. The magnet in the figure is 12 mm thick and weighs 40 grams, and the shell and top plate contribute to a total system weight of over 100 grams. Fig. 15-16B show the magnetic flux density, magnetic flux distribution, field line model, and overall geometry of the present example. This configuration results in a magnet depth of 18.5 mm that is too deep to be used in a flat panel speaker. The increased magnet weight also makes this design more expensive than the dual ring design shown in fig. 1.

Thus, it can be seen that the double ring magnet design has a high magnetic flux density with a low weight. By comparison, conventional designs with the same magnetic flux exhibit the disadvantages of being too deep, too heavy, and too expensive. The loudspeaker of the present invention not only effectively concentrates the effective flux in the narrow, shallow voice coil gap, but the central opening of the dual ring design also defines the path of the movable voice coil power line. The manufacturing cost of the loudspeaker is reduced by omitting the delicate step of connecting the driving circuit with the fixed voice coil joint in the loudspeaker. It also allows for smaller component sizes (since space around the circumference is not required for wiring) and simplifies the enclosure mounting method. The energy extracted from the neodymium is highly efficient, thereby improving the acoustic efficiency of the linear drive motor. As described above, the apertured magnet may also reduce the effect of stiffness of the speaker enclosure or communicate an external tuning enclosure with air to attenuate or tune the response in the combined speaker/enclosure system.

Further variations and modifications of the invention and the described embodiments, and its implementation, may occur to those skilled in the art and are within the scope of the appended claims and their equivalents.

Claims (8)

1. A magnet assembly for a loudspeaker, the assembly comprising:

first and second annular magnets coaxially disposed and defining a radial gap therebetween, said first and second magnets being axially polarized;

a shunt spanning and connecting one side of said first and second magnets;

a first pole piece having a first working surface, said first pole piece disposed above the first magnet; and

a second pole piece having a second working surface, said second pole piece being disposed over the second magnet;

the member first and second working surfaces define a voice coil gap therebetween such that magnetic flux is concentrated in the voice coil gap and a central opening is provided through the member.

2. The magnet assembly of claim 1, wherein the first and second magnets are rare earth magnets.

3. The magnet assembly of claim 1, wherein the first and second magnets are neodymium magnets.

4. A speaker includes:

a film;

a voice coil connected to the membrane; and

a magnet assembly defining a flux gap in which the voice coil is disposed, the magnet assembly comprising a pair of concentrically arranged ring magnets, a shunt interconnecting the magnets on one side of the magnets, and a pair of pole pieces on the other side of the magnets to effectively concentrate the flux in the voice coil gap formed by the opposed working faces of the pole pieces.

5. The speaker of claim 4, wherein the power conductor of the voice coil passes through the center of the magnet assembly.

6. A loudspeaker as claimed in claim 4, wherein the magnet member has a central opening to allow air communication with the rear space of the loudspeaker.

7. The loudspeaker of claim 6, further comprising a housing, wherein the central opening is connected to the housing.

8. A method of manufacturing a loudspeaker component, the method comprising the steps of:

providing a magnet member having a central opening through the member and a magnetic gap;

placing the voice coil in the gap of the first side of the magnet member; and

the voice coil drive circuit is passed through the opening to the second side of the magnet member.