GB2416951A - Loudspeaker unit - Google Patents

Abstract

A loudspeaker unit comprises at least one diaphragm <B>8</B> adapted to be coupled to a generator <B>1</B>,<B>2</B> for converting electrical signals to movements in the diaphragm, the diaphragm constituting part of a wall in a chamber, the chamber having a wall opposing the diaphragm and side walls on at least two sides of the chamber, the chamber defining an opening in a position perpendicular to the diaphragms direction of movement, the opening having a cross section area being substantially smaller than the area of the diaphragm.

Description

LOUDSPEAKER UNIT

The present invention relates to a loudspeaker unit according to the preamble ol' the enclosed claim 1.

A conventional loudspeaker has a magnet and a voice spool that is moveable in the magnetic field of the magnet. The voice spool is connected to a membrane, which is usually cone shaped but also may be planar. 'I'he outer edge of the membrane is connected to a frame via a flexible surround part. All the sound is produced by this one membrane. The sound output is related to the amount of air that is moved by the membrane. This is dependent on two factors, the distance the membrane is capable of moving and the area of the membrane. Since the distortion of the sound generally will increase as the movement distance of the membrane increases the loudspeakers with the highest output generally have very large membranes. However, this may result in wobbling of the membrane and hence distortion of the sound. Moreover, large speakers are more difficult to handle physically and takes more space.

Attempts have been made to increase the amount of air that can be moved by using several membranes, thus being able to use smaller membranes. One such constructions is shown in US 4107479. This is a construction comprising several membranes coupled together via common driving means. The membranes are placed horizontally and plates are situated at an angle to the membranes to reflect the sound towards the listener. No effective dampening of resonance frequencies occurs.

Another construction is shown in WO 99/07183. In this loudspeaker unit a membrane folded like an accordion is placed between two magnets. The membrane carries an electrical conductor. By energising the electrical conductor the folds of membrane can be brought together and apart, thus making the air between the folds vibrate. This loudspeaker construction is used for high frequency loudspeaker elements only (tweeters and middle range). The membrane containing electrical conductors is very expensive. It is not realistic to make a bass speaker according to this construction since a large unsupported membrane of this type easily would start wobbling in a direction transverse to the intended folding and unfolding movement.

he loudspeaker unit according to the invention contains a drive unit that produces sound waves similar in function to a conventional magnetic dynamic loudspeaker.

One of the objects of the present invention is to provide an effective dampening of the resonance frequencies of the diaphragm.

'I'he invention has as one object to provide for a loudspeaker unit that can be made much smaller than a conventional unit required to produce the same amount of sound waves, and allows the cone to travel a longer distance without the introduction of distortion due to the cone wobbling.

Another object of the invention is to provide for a loudspeaker unit that can move a larger amount of air required for making the sound in a smaller unit.

Still another object of the invention is to provide a unit that is modular in fashion and allows for the drive unit to be scaled up or down in size. reducing production costs for different sized drive units.

he invention relates to an acoustical loudspeaker, which may be used to transduce electrically modulated signals into sound waves. In a preferred embodiment, contrary to known speakers, it utilises from one to N number of membranes, driven by one or many electro-acoustical magnet systems, and it is mounted at a 90 degree angle to conventional drive units.

One or more oi'the above objectives is achieved by a loudspeaker unit comprising at least one diaphragm adapted to be coupled to a generator means for converting electrical signals to movements in said at least one diaphragm, said at least one diaphragm constitutes part of a wall in a chamber, said chamber including a wall opposing the diaphragm and side walls on at least two sides ofthe chamber, said chamber defining an opening in a position perpendicular to the diaphragms direction of movement, said opening having a cross section area being substantially smaller than the area of the diaphragm.

In a preferred embodiment the opposing wall is essentially parallel to the diaphragm.

This will enhance the dampening effect.

In another embodiment the opposing wall has an angle relative to the diaphragm, so that the distance between the diaphragm and the opposing wall increases toward the opening. This gives flexibility as to how much dampening the loudspeaker unit is provided with.

Preferably, the angle between the opposing wall and the diaphragm is less than 20 degrees, preferably less than 10 degrees. This will give a significant dampening of the resonance frequencies.

In a preferred embodiment the loudspeaker unit comprise one chamber on each side of the diaphragm. This will give the possibility to redirect and make better use of the sound generated on the opposite side of the diaphragm.

h1 a preferred embodiment of the invention the second chamber has an opening in the opposite direction relative to the first chamber. This will prevent sound from the two chambers, which are in counter phase, to destroy each other.

Preferably, the opening and the inner surfaces of the chamber or chambers are provided with rounded or non-linear shapes. This will prevent edge el'fects from the air flowing past and reduce standing waves, resonances.

Preferably, the distance from the diaphragm to the opposite wall is between 110% and 200% of the maximum travel of the diaphragm. This is an optimum between avoiding a squeeze effect and achieving a good dampening.

According to a preferred embodiment the invention also relates to a loudspeaker comprising at least two loudspeaker units wherein said loudspeaker units arc coupled to at least one generator means Nor converting electrical signals to movements, said diaphragms are coupled to said generator means though a rod being fastened to each diaphragm, so as to move synchronously to the generated movements. This will result in a loudspeaker having a larger output compared to the size.

In a preferred embodiment the loudspeaker comprises of two generator means, being positioned at the opposite sides of said rod. This gives a high input of energy to the 1 0 loudspeaker.

The invention will in the following be described in detail with reference to a preferred embodiment shown in the enclosed drawings, in which: Figure I shows the loudspeaker unit in perspective, Figure 2 shows a longitudinal section through the loudspeaker unit, Figure 3 shows a longitudinal section through the loudspeaker unit, in a plane perpendicular to the plane of figure 2, Figure 4 shows a diagram of the possible dampening using chambers coupled to the loudspeaker unit.

Figure I shows a perspective view of the loudspeaker unit. It comprises a first loudspeaker element I and a second loudspeaker element 2. 'I'he two loudspeaker elements arc facing each other and are connected with each other via bars 3 - 6.

Between the loudspeaker elements I and 2 is a membrane assembly 7, which has a number of generally planar membranes or diaphragms 8.

The detailed structure of the loudspeaker unit of the invention will be explained referring to figures 2 and 3. These figures show longitudinal cross section transverse to each other.

'I'he loudspeaker units 1, 2 are principally identical. Thus only one will be explained in detail. The following description of the unit I will also apply for unit 2. The loudspeaker unit I has a permanent magnet 11, that has a first pole 12 at a first surface 14 and a second pole 13 at a second surface 15. The magnet 11 may be a ring shaped magnet with a central cavity 19 or consist of two or more magnets arranged with the ] O poles in the same direction around a central cavity 19.

Furthermore, the loudspeaker unit has a first pole piece 16 against the first pole 12 and a second pole piece 17 against the second pole 13 of the magnet 11. The second pole piece 17 has a centrepiece 18 that extends into the cavity 19. The centrepiece may be massive or have a bore 50, as shown. Between the centrepiece and the first pole piece are two air gaps 20 and 21 over which a magnet field is created.

A coil assembly 22 with a voice coil 23 is arranged so that the voice coil is substantially situated within the air gaps 2(), 21. The coil assemblies are supported by a spider 24.

The spider 24 is a flexible member that surrounds the coil assembly 22 and allows substantially free movement of the coil assembly in a direction transverse to the plane of the spider 24. 'The spider 24 is at the outer edge supported by a spider plate 25 that in turn is firmly supported by a first set of pins 26. These parts are also shown in figure 1.

Via second set of pins 27 the first pole piece 16 is connected to the spider plate 25 (see also figure 1). 'I'hus the magnet 11, the pole pieces 16, 17 and the spider plate 25 form a rigid structure.

The first set oi'pins 26 are connected to a box structure 28 containing the membrane assembly 7. The box structure consists ol'a number of cases 29a - f. The cases 29a - f arc interconnected by a common panel 30a - c and 31 a and b. The panels 31 a and 31 b are solid panels and the panels 30a - c have an opening within which a membrane 32 a - c is situated, so that the membrane 32 a - c forms a common panel of the two adjoining cases. Every second case 29a, 29c, 29e has an open end 34a - c facing in a first direction and every other second case 29b, 29d, 29fhas an opening 35a- c facing in a second opposite direction. The two cases 29a and 29f; facing a respective loudspeaker unit 1, 2 have a solid panel 36a, 36b lacing the respective loudspeaker units 1, 2. Except for the open ends 34a - c, the cases have solid side panels 37a - k and end panels 38a- f. I he panels 37a - 1 may have a quarter- hollow in the intersection with the panels 36a- b and 31a- b, as shown in figures 1 and 2. The panels 37a- I may also be full hollow, i.e. having no sides at all (not shown), the structure being supported by pins located between the adjacent panels. The panels 38a may also have a quarter-hollow in the intersection with the panels 36a - b and 31 a - b and be convex on the outside of the box structure.

The spider plates of the two loudspeaker elements 1, 2 are interconnected by the set of (four) bars 3 - 6.

Between the coil assemblies 22 of the two loudspeaker elements 1, 2 a pull-push rod 39 is extending. The rod 39 is firmly connected to the coil assemblies 22 at a respective end. The rod 39 extends through a hole 40a d through the panels 36a, 3 la, 31 b and 36b. The holes are slightly larger than the cross section of the rod 39, so that the rod may move longitudinally unrestricted in the holes 40a - d. Preferably, the annulus between the edge of the holes 40a - d and the rod 39 is filled with felt 51, cotton or another suitable substance, which will make a reasonably air tight seal without restricting the movement ol the rod 39.

The rod 39 also extend through the membranes 32a - c, but the membranes are connected to the rod 39 (preferably glued), so that when the rod moves the movement will be transferred to the membranes. The membranes 32a - c are preferably relatively stiff so that when the membrane 32a - c is pushed or pulled by the rod 39, the whole membrane will move the same distance. At the outer edge the membranes 32a - c are connected to a flexible surround part 41, that has a dome shaped cross section and extends around the perimeter of the membrane 32a - c. The flexible surround part 41 is at the outer edge connected to the panel 30a - c. Preferably, the membranes have a square shape' as this will give the largest radiating area, but they may also be circular, oval or any other feasible shape.

From the above description it is evident that the loudspeaker unit consists of moveable parts and stationary parts. The moveable parts are the coil assemblies 22 with the voice coil 23, the push-pull rod 39 and the membranes 32a c. These parts will move as one unit and are supported by the spiders 24 and the flexible surround parts 41, which are connected to the stationary parts. The stationary parts are constituted by the remaining parts described.

When an amplifier (not show) is connected to the loudspeaker elements 1, 2 the two loudspeaker elements will be coupled so that they move in counter phase. Preferably, this is done by switching the leads from the amplifier that extends to one of the loudspeaker elements. Alternatively, one of the loudspeaker units may have magnets with opposite poles, although this is not preferred since it would require two different types of loudspeaker units.

As the loudspeaker elements are energised the coil assemblies 22 will push and pull on the rod 39, which in turn transfers the movement to the membranes 32a - c. The membranes will compress the air contained in the cases 29. When the membranes move downward (referring to the orientation shown in figures 2 and 3) the air in the cases 29a, 29c and 29e will be compressed and ejected through the open ends 34a, 34b, 34c facing in a first direction. When the membranes move upward the air in the cases 29b, 29d and 29f will be compressed and ejected through the open ends 35a - c facing in a second direction. Since the operating in synchronicity are ejecting to the same side, whereas the cases operating in counter phase emits sound in opposite directions, the air emitted from one case will not be immediately sucked into the adjoining case, as would be the case if all cases had the open end facing in the same direction.

Consequently, the sound will be emitted in two opposite directions. l'o re-direct the sound of one of the directions, the loudspeaker unit may be built into an enclosure having a back wall that reflects sound.

Baffles 52 may be placed in front of and at a small distance from the openings 34a, b and c. These Lames may be made of long haired wool or glass fibre or any suitable material.

I'he moveable parts have a light weight, which is important in loudspeakers, since heavy parts have a larger inertia requiring more power to move. Furthermore, heavy parts will have a tendency to distort the sound.

The number of cases 29 can be varied depending on the output of sound required.

Preferably, the loudspeaker elements 1, 2 are dimensioned so that the same loudspeaker elements can be used for a wide variety in number of cases. Thus, the stock keeping of parts can be simplified. In fact the cases 29 can be produced as standard cases of two types only, both of which have one top or bottom panel only, a first type with a top/bottom panel 30 including a membrane 32 and a second type including a top/bottom panel 31 that is solid. By assembling these to types oi cases so that every second case is of the first type and every other second case is of the second type, and closing of the cases at each end with a end panel 36, a box structure 28 of any number of cases 29 can be made.

The length of the pull-push rod 39 and the length of the bars 3 - 6 will have to be adapted to the length of the box structure 28. However, since these parts have a uniform cross section throughout their length, it is possible to cut these into the required length.

The push-pull rod 39 may also extend through the loudspeaker elements I and 2, as shown in figure 2 at the loudspeaker element 2, so that it can extend into a second loudspeaker unit. Thereby, the two units may work as one with, e.g., four loudspeaker elements, thus increasing the stability control of the pull-push rod and increasing the power handling of the drive unit, as well as the effectiveness at which the diaphragms return to the original rest position after reproducing a sound based on the electrical input signal. This improves the faithfulness of the signal being reproduced.

The unit as shown in the figures has two spider suspensions holding the pull-push rod in place. The unit can according to the above have one to any number of spider suspensions.

Consequently, it is possible to make loudspeaker units of different sizes with the same standardized parts.

Turning back to figure 1, this shows a loudspeaker unit according to the invention connected to a box structure 60 comprising three resonance compartments 61, 62, 63. A respective one ofthe compartments 61, 62, 63 is in communication with the openings 34a, 34b and 34c. The compartments 61, 62, 63 may have a port (not shown), preferably near the opposite end of the loudspeaker unit, that the sound can be emitted from. The size and shape of the compartments and the ports may be varied to adapt the loudspeaker to the resonance frequency of the diaphragms. E.g., by providing ports with different sizes for each compartment 61, 62, 63, the resulting resonance frequency of the loudspeaker can be dampened.

The graph in figure 4 shows how a frequency response curve 65 with a peak resonance frequency at about 60 hertz can be dampened to a frequency response curve 66 with smaller peaks 67 at a much lower level.

Preferably, the box structure has a bottom plate 68 and a top plate 69. The loudspeaker unit may be fixed to the top plate 69 by an appropriate fastening means, e.g., pins 70, so that the box structure can function as an integrated stand for the loudspeaker.

By using a larger number of cases the membranes can be of a smaller size than a membrane of a conventional loudspeaker unit. This results in a faster subjective transient response and allows more opportunities for tuning of the sound of the drive unit. Also, the sizes and/or damping of each chamber in the loudspeaker unit itself may be varied to distribute the resonance frequencies of'the loudspeaker.

With this invention damping is achieved as the air in the chamber in front of and behind of the diaphragm is uniformly pressed out of the top or bottom of the chamber, thus travelling along the diaphragm at a 90 angle from the direction of the diaphragm. The travelling speed wi 11 be faster than that of the speed of the diaphragm, thus reducing wobbling and flexing of the diaphragm.

In the enclosed l'igures of the embodiment described, the surface opposing the membrane or diaphragm is parallel to the diaphragm. This is the optimal solution, but in an alternative embodiment of the invention this, however, may be varied. 'l'hc unit wall adjacent to the diaphragm can have an up to 20 lean toward the diaphragm. but this would increase the damping so much that the diaphragm would start to compress the sound being reproduced, thus not reproducing the input signal faithfully. If the unit wall adjacent to the diaphragm has up to 44 lean away from the diaphragm' this would lessen the effect of the damping thus negating the benefit. Thus the unit wall adjacent to the diaphragm works best when working within the +/- 10 lean range.

I S The optimum depth of the chamber, from diaphragm to the adjacent wall could be defined as; the maximum travel of the diaphragm (Xmax) + 10%. This would allow for the diaphragm to travel its maximum course with a little room to spare for over-driving.

As the drive unit is driven harder, the damping effect will be increased as the amount of air in the chamber is reduced and the speed of the air is increased. Thus damping will increase when it is most needed, that is when the drive unit is driven at high levels.

The chamber depth can, however, be increased up to maximum travel of the diaphragm + 200%, but the effect of the damping would be greatly reduced.

further damping of the wobbling and resonant frequency can be achieved by adding the damping mats or baffles 52 to the opening of the chamber venting into the compartments 61, 62, and 63 of the box 60. This has the effect of reducing the speed of' the air expelled from the chamber into the compartment, thereby increasing the control of the diaphragm at the resonant frequency.

The loudspeakers shown in the embodiment of the figures, vents the sound in the opposite direction to the compartments it is loading into. T his does not have to be the case. The sections venting the sound can be turned to vent in four diffferent directions or all directions based on the number of diaphragms used. The panels can all be vented, e.g. at the following angles to the box 60: 90 , 180 (this would be as shown in the figures), 270 , 360 (the same direction as the box 60) or 0 .

I'he unit can also allow each diaphragm, if sufficient diaphragms are used, to vent at all of the above angles, by having diaphragms venting at 90 from the box, 180 , 270 , 360 and 0 .

The unit as shown in the figures has two magnet systems generating movements to the diaphragms, this number may of course vary from one to any suitable number. Also, the illustrated magnet systems have the magnets placed at either end of the drive unit. This does not have to be the case. The magnet systems can be placed at any point along the pull- push rod. The magnet system can thus be placed between the panels enabling a completely hidden magnet system for protection of the magnet systems.

Summarizing, the advantages that can be achieved by the present invention may be listed as follows: - The loudspeaker has a smaller footprint than a conventional electro dynamic drive unit of the same vibrating surface area.

- It uses two or more separate magnet structures in a pull-push configuration in one drive unit.

- It uses multiple cones driven as a single cone.

- It allows for the cones to travel a grater distance along one plane without distorting the signal being reproduced.

- It allows for greater thermal cooling with the use of aluminium for the push rod, enabling greater power handling.

- It enables simple building of a drive unit and flexibility when producing different sizes of drive units.

- And it allows a simple damping cap to be used to reduce the total 'Q' of the drive unit' thus reducing the required box loading size.

Claims (4)

1. C I a i m s 1.

   Loudspeaker unit comprising at least one diaphragm adapted to be coupled to a generator means for converting electrical signals to movements in said at least one diaphragm, said at least one diaphragm constitutes part of a wall in a chamber, said chamber including a wall opposing the diaphragm and side walls on at least two sides of the chamber, said chamber defining an opening in a position perpendicular to the diaphragms direction of movement, said opening having a cross section area being substantially smaller than the area of the diaphragm.
2. 2.

   Loudspeaker unit according to claim 1, wherein the opposing wall is essentially parallel to the diaphragm.
3. 3.

   Loudspeaker unit according to claim l, wherein the opposing wall has an angle relative to the diaphragm, so that the distance between the diaphragm and the opposing wall increases toward the opening.
4. 4.

   Loudspeaker unit according to claim, wherein the angle between the opposing wall and the diaphragm is less than 20 degrees, preferably less than 10 degrees.

   Loudspeaker unit according to claim I, comprising one chamber on each side of the diaphragm. 6.

   Loudspeaker unit according to claim 5, wherein the second chamber has an opening in a different or the same direction relative to the first chamber, or no chamber at all. 7.

   Loudspeaker unit according to any one of the preceding claims wherein the opening and the inner surfaces of the chamber or chambers are provided with rounded or non-linear shapes. 8.

   Loudspeaker unit according to claim 1, wherein the distance from the diaphragm to the opposite wall is between 1 10% and 200% of the maximum travel of the diaphragm. 9.

   Loudspeaker comprising at least two loudspeaker units according to any one of claims 1-8, said loudspeaker units being coupled to at least one generator means for converting electrical signals to movements, said diaphragms being coupled to said generator means though a rod being fastened to each diaphragm, so as to move synchronously to the generated movements. 10.

   Loudspeaker according to claim 9' comprising two or more generator means, being positioned at the opposite sides of said rod.