WO2006117716A1

WO2006117716A1 - Loudspeaker having a movable diaphragm

Info

Publication number: WO2006117716A1
Application number: PCT/IB2006/051275
Authority: WO
Inventors: Frederick J. K. Kwek
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-05-02
Filing date: 2006-04-25
Publication date: 2006-11-09

Abstract

A loudspeaker is provided with a frame (32a, 32b), a movable diaphragm (33), a suspension (36) surrounding the movable diaphragm (33) for suspending the diaphragm (33) in the frame (32a), and a plurality of voice coils (37a, 37b, 37c) attached to the diaphragm (33) and an arrangement of magnets (38a, 38b, 38c, 38d) in which the plurality of voice coils is inserted into gaps formed in the arrangement of magnets. The suspension comprises an S-shaped part (36) surrounding the diaphragm.

Description

Loudspeaker having a movable diaphragm

FIELD OF THE INVENTION

The invention relates to a loudspeaker provided with a frame, a movable diaphragm, a suspension surrounding the movable diaphragm for suspending the diaphragm in the frame, the suspension being attached to a peripheral part of the diaphragm, and a plurality of voice coils attached to the diaphragm and an arrangement of magnets in which the plurality of voice coils is inserted into corresponding gaps formed in the arrangement of magnets.

BACKGROUND OF THE INVENTION Speakers of such a type are known from United States Patent 4,438,297, which discloses a loudspeaker with a flat diaphragm. In operation, the flat diaphragm is driven by a plurality of voice coils. The voice coils are inserted between magnetic poles and driven by a magnetic circuit including an arrangement of magnets magnetized in the same direction as the vibration of the coils. At its periphery, the diaphragm is suspended on the frame by a suspension.

Currently, there is a demand for flat, light-weight and high-efficiency loudspeakers on the audio and loudspeaker market. Although the known loudspeaker has certain advantages, it requires a rather large height.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a loudspeaker of the type described in the opening paragraph which allows a flat design.

To this end, the loudspeaker according to the invention is characterized in that the suspension comprises an S-shaped part surrounding the diaphragm. In the prior-art loudspeaker, the suspension surrounding the flat diaphragm is

U-shaped. A so-called spider is provided at some distance below the U-shaped suspension and the flat diaphragm. The provision of this spider has a number of positive and negative effects. The positive effect is that the movement of the voice coils is guided, which reduces vibrations sideways. However, the provision of the spider increases the depth and weight of the loudspeaker, and the design loses some of the effective depth for voice coil interaction with the magnetic gap, reducing the efficiency. By using an S-shaped surround, a spider is no longer needed. This reduces the height and weight of the loudspeaker and increases its efficiency. A single S-shaped surround is used in embodiments in which the diaphragm has a relatively small excursion.

If a larger excursion is needed, a multiple S-shaped surround can be used for such a design.

In preferred embodiments, the magnetic arrangement is a single-layer multiple magnet array. In the prior-art document, a magnetic array comprising several layers is described. Use of a single layer decreases the height of the loudspeaker and increases its efficiency.

It is noted in relation to the claims that various combinations of characteristic features defined in the claims are possible. The above-mentioned and other aspects of the invention are apparent from and will be elucidated, by way of non- limiting example, with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

Figure 1 shows an example of a standard loudspeaker with a cone-shaped diaphragm.

Figure 2 illustrates a design as shown in United States patent 4,438,297. Figure 3 illustrates a loudspeaker according to the invention. The Figures are not drawn to scale. Generally, identical components are denoted by the same reference numerals in the Figures.

DESCRIPTION OF EMBODIMENTS

A standard electrodynamic loudspeaker 1 shown in Figure 1 comprises a frame 2, a movable cone-shaped diaphragm 3 and an electromagnetic actuator 4 for actuating the diaphragm 3 to make it move in a translational direction T.

The diaphragm 3_ is connected to the frame 2 via a surround 6. The surround 6 is U-shaped and is formed, for example, from a bent rubber or foam annular strip. On its outer circumference, the surround 6 is secured, for example glued, to the frame 2 and on its inner circumference to an outer circumferential edge (i.e. a peripheral part) of the cone- shaped diaphragm 3. The cone-shaped diaphragm 3 is connected to an actuator housing 7. A further diaphragm 8 extends between the chassis 2 and the actuator housing 7 and is connected to both. This further diaphragm 8, also called a spider, ensures that the diaphragm 3 can perform well-defined translation movements along direction T with respect to the frame 2. A dust cap 9 is conventionally provided on the actuator housing 7. The standard loudspeaker thus comprises a resilient surround 6 for suspending the diaphragm 3 from the frame 2 and for guiding the movable body along a translation axis T. The suspension system thus includes a U-shaped resilient surround 6 between an outer circumference of the diaphragm 3 and the frame 2, and spider 8 between the chassis 2 and the actuator support 7. It is known per se to reduce the height of the loudspeaker by using a flat (or flatter) diaphragm. Such a design is known from United States patent US 4,438,297. The design known from this patent is shown in Figure 2.

The loudspeaker comprises a flat diaphragm 13 which is suspended by U- shaped suspension 16 in frame 12. Attached to the flat diaphragm is a plurality of voice coil holders 22, which are provided with voice coils 23. The voice coils are inserted into gaps in the arrangement 23 of magnets. The arrangement 23 is attached to the frame 12. A spider 18 is attached to the voice coil holder 22 and to the frame 12. It is to be noted that the suspension of the diaphragm in the standard design as well as in the design of Figure 2 has two basic elements, the U-shaped suspension 6, 16 and the spider 8, 18.

Although the known design often operates satisfactorily, there remains a need for improvement, especially leading to much flatter loudspeakers. The distance between the flat diaphragm and the arrangement of magnets is relatively large.

Figure 3 illustrates a loudspeaker according to the invention. The loudspeaker comprises a diaphragm 33, which is provided with a plurality of voice coils 37a, 37b, 37c. The diaphragm is suspended in a frame 32 (consisting of ring-shaped part 32a and bottom part 32b) by means of an S-shaped suspension 36. This suspension is tensioned. "S-shaped" is herein understood to mean any form comprising a sequence of at least two half waves wherein adjacent half waves have opposite signs. Thus a double S or triple S form is also understood to be "S-shaped". The "waves" may be round or have folds. This also includes a form which is best described by an S shape followed by a single U. An S-U shape (i.e. three half waves) or an SS-U shape (five half waves) is thus also included. The voice coils 37a, 37b and 37c are inserted into gaps in a magnetic arrangement comprising, in this example, magnets 38a to 38d. The S-shaped tensioned suspension 36 allows a much smaller distance between the diaphragm 36 and the magnetic arrangement, leading to a reduced height and a smaller risk of distortion. Consequently, there is no need for a spider. This allows a flatter design, because the distance between the diaphragm and the magnetic arrangement can be reduced, and also a simpler design, because at least the spider is no longer needed. Moreover, the loudspeaker according to the invention has a reduced weight, because it has a smaller height so that its frame can be made smaller and the use of a spider can thus be dispensed with.

The magnetic arrangement is preferably composed of a single layer of magnets magnetized in a direction along the direction of movement. In comparison with the design shown in Figure 2, this yields a flat design allowing a further reduction of height.

It is to be noted that, in comparison with the known design, the design according to the invention leads to an increase of the overall diameter of the loudspeaker. However, this increase of diameter is not significant for small drivers. The current challenge for manufacturers of loudspeakers is the slimmest design possible, squeezing out every inch of acoustical air/wave from the transducers.

It is also to be noted that the surround helps keep the diaphragm centered and provides the restoring force that retains the coils in the magnetic structure. The surround also provides a damped termination (damping the vibration modes) for the diaphragm edge. With the right stiffness, the surround will prevent voice coils from bottoming onto the magnetic structure. The stiffness or the reciprocal of the stiffness, the mechanical compliance, of the S(SS) surround which can be made of cloth, fiber glass, nylon fiber, kelvar, carbon fiber, rubber, foams, etc. can be controlled by doping plastic, rubber, silicon, fiber with epoxy, acrylic paint coating, etc. It is noted that, in the known designs, the mechanical compliance of the suspension system for the diaphragm is largely formed (up to 90%) by the spider. In the loudspeaker of the invention, the mechanical compliance is provided by the S-shaped surround, resulting in surrounds that have substantially different mechanical compliances than those for the known U-shaped surround design. The mechanical compliance will vary in dependence on the type of driver characteristic requested. For example, the cone/diaphragm will normally be very stiff for a tweeter, i.e. a very low compliance. For a woofer, however, , the cone must move easily so as to generate large amounts of moving air, i.e. a high compliance or a less stiff cone is required. A compromise is most suitable for a mid-range driver.

For example, a typical 8" woofer with Fs=30 Hz, Vas=60L, Qms=2.40, Qes=0.42, Qts=0.36, Re=6.25 ohms, may have the following mechanical parameters: -3 Cms (mechanical compliance) = 1.01 x 10 m/N,

-3

Mms = 27.9 x 10 kg,

Rms = 2.19 kg/s Bl = 8.84 N/A

Materials suitable for the linen treatment are rubber (rubber compound called NBR), foam, or injected Santoprene. Rubber yields the smoothest response with the fewest anomalies and is generally one of the best edge damping materials to be used for a surround in which a smooth upper frequency response is an aspect of consideration.

In summary, the invention can be described as follows.

A loudspeaker is provided with a frame (32a, 32b), a movable diaphragm (33), a suspension (36) surrounding the movable diaphragm (33) for suspending the diaphragm (33) in the frame (32a), and preferably a plurality of voice coils (37a, 37b, 37c) attached to the diaphragm (33) and an arrangement of magnets (38a, 38b, 38c, 38d) in which the plurality of voice coils is inserted into gaps formed in the arrangement of magnets. The suspension comprises an S-shaped part (36) surrounding the diaphragm. The S-shaped surround allows a flatter design of the loudspeaker, leading to less distortion.

For instance, the loudspeaker may have a form deviating from a circular form, for instance, an oval form.

In the examples, the movable diaphragm is shown as a flat diaphragm. The invention is particularly advantageous for loudspeakers having a flat diaphragm. "Flat" is understood to mean that the diaphragm, when not excited, is flat. "Flat" is not to be interpreted so restrictively as in the mathematical sense of the word, but rather in a practical sense. This means that diaphragms may be used which are relatively shallow, especially those which are slightly cone-shaped. The loudspeaker preferably comprises a plurality of 2 to 5, more preferably 3 voice coils.

It will be evident to those skilled in the art that many variations are possible within the scope of the invention which is not limited by what has been particularly shown and described hereinbefore. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Reference numerals in the claims do not limit their protective scope. Use of the verb "comprise" and its conjugations does not exclude the presence of elements other than those stated in the claims. Use of the article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

CLAIMS:

1. A loudspeaker provided with a frame (32a, 32b), a movable diaphragm (33), a suspension (36) surrounding the movable diaphragm (33) for suspending the diaphragm (33) in the frame (32a), the suspension being attached to a peripheral part of the diaphragm, and a plurality of voice coils (37a, 37b, 37c) attached to the diaphragm (33) and an arrangement of magnets (38a, 38b, 38c, 38d) in which the plurality of voice coils is inserted into corresponding gaps formed in the arrangement of magnets, wherein the suspension comprises an S-shapedpart (36) surrounding the diaphragm (33).

2. A loudspeaker as claimed in claim 1, wherein the suspension comprises a single S-shaped part.

3. A loudspeaker as claimed in claim 1, wherein the suspension comprises a multiple S-shaped part.

4. A loudspeaker as claimed in claim 1, wherein the magnetic arrangement is composed of a single layer of magnets magnetized in a direction along the direction of movement.

5. A loudspeaker as claimed in claim 1, wherein the diaphragm is a flat diaphragm (33).