WO2008093238A2

WO2008093238A2 - Loudspeaker with ventilation shafts for air gap cooling

Info

Publication number: WO2008093238A2
Application number: PCT/IB2008/000449
Authority: WO
Inventors: Alex Geltmeyer
Original assignee: Pss Belgium Nv
Priority date: 2007-02-01
Filing date: 2008-01-31
Publication date: 2008-08-07
Also published as: WO2008093238A3; WO2008093238A8

Abstract

A loudspeaker comprises a chassis (1) having a front (Ia), a diaphragm (3) movably suspended from the chassis, and an electromagnetic driver (5) for driving the diaphragm with regard to the chassis. The driver includes a magnet system (7) connected to the chassis and a voice coil (9) connected to the diaphragm to cooperate with the magnet system via an air gap (11). In order to create sufficient cooling capacity at least one ventilation shaft (30) is provided which is connected to at least one ventilation hole (40) in the magnet system and which ends in or near the front of the chassis, wherein the at least one ventilation hole is in communication with the air gap.

Description

Loudspeaker with movable diaphragm

The invention relates to a loudspeaker comprising a chassis having a front, a diaphragm movably suspended from the chassis, and an electro-magnetic driver for driving the diaphragm with regard to the chassis, which driver includes a magnet system connected to the chassis and a voice coil connected to the diaphragm to cooperate with the magnet system via an air gap.

Such loudspeakers are generally known and marketed in a variety of embodiments. A common feature of these conventional loudspeakers is that they each comprises a chassis carrying a magnet system and a diaphragm, by means of which chassis the loudspeaker can be mounted in a housing or an apparatus. A voice coil connected to the diaphragm cooperates with the magnet system via an air gap to drive the diaphragm. When the voice coil is energized heat is generated resulting in a temperature rise in the magnet system. Most common magnet materials used in nowadays conventional loudspeakers are ferrite and neodymium materials. Both kinds of materials are suitable to build satisfying magnet systems. A neodymium magnet system has, compared with a ferrite magnet system with a same magnetic power, the advantages to be smaller in size and lighter in weight. The market is more and more asking for using neodymium magnets in loudspeakers in order to save weight and space. A disadvantage of a neodymium magnet system is its relatively small thermal power capacity in comparison with the thermal power capacity of a comparable ferrite magnet system. This disadvantage is a consequence of the relatively small thermal radiation surface and the relatively low mass of the neodymium magnet system. A neodymium magnet system heats up faster and reaches higher temperatures at higher power levels than a comparable ferrite magnet system. A rising temperature is cause of thermal compression, i.e. a loss of sensitivity due to warming up of several components of a loudspeaker. A temporary decreasing magnetic force is the result of warming up the neodymium magnet system also resulting in a lower sensitivity. In the case that the temperature in a neodymium magnet system comes above about 110⁰C a permanent decrease of magnetic force is caused. A rising internal resistance in the voice coil is caused by a higher temperature in the magnet system, resulting in an additional lost on sensitivity. Concluding it can be stated that a higher power level causes several problems in neodymium magnet systems. In traditionally designed loudspeakers the voice coil is suspended from the chassis by means of a flexible centering element, also called spider. In these loudspeakers air is captured between the spider and the magnet system. This air warms up, during use of the loudspeaker, together with the magnet system and therefore does not give cooling to the magnet system.

An object of the invention is to provide a loudspeaker which is cooled sufficiently during use in order to prevent loss of performance.

This object is achieved by the loudspeaker according to the invention, as defined in claim 1. The loudspeaker according to the invention is particularly characterized by the presence of at least one ventilation shaft which is connected to at least one ventilation hole in the magnet system and which ends in or near the front of the chassis, wherein the at least one ventilation hole is in communication with the air gap.

Due to the presence of one or more ventilation shafts and the presence of one or more ventilation holes being in communication with the shaft or shafts fresh air coming from the available outside air volume near the front of the loudspeaker is supplied to an inner space enclosed by the magnet system, during use of the loudspeaker. In this way a very efficient cooling of the driver is obtainable. This is particularly of importance for bass and midrange loudspeakers, which need an optimized cooling in case of high power levels. The fresh air supply through the ventilation shaft or shaft is caused by air displacements inside the driver during energizing the voice coil. During energizing the voice coil, its coil support and the diaphragm make translation movements with regard to the magnet system, causing said air displacements.

The ventilation shaft may be embodied in a variety of ways, e.g. as a tube, duct, pipe and channel. Moreover the ventilation shaft can have several shapes and lengths.

In an alternative solution use is made of only holes in the magnet system, which holes extend from an inner side to an outer side of the magnet system. Displacements of air caused during translation of the voice coil indeed create inflow through the holes, however, the supplied air from the surrounding area of the magnet system is in general insufficiently cool air. A reason for this is that in general the loudspeaker is a built-in speaker, wherein the air volume around the magnet system is rather small and substantially closed. The air in such volume warms up together with the magnet system and mostly reaches a stable but too high temperature for best performance of the driver and thus the speaker. Due to the use of ventilation shafts the cooling of the driver of the loudspeaker according to the invention is totally independent from the air present around the magnet system. This aspect is particularly advantageous in automotive environments, because in those applications loudspeakers are mostly integrated in dashboards and doors, which rooms can reach very high temperature even simply by entering rays of sun. In such cases thermal compression already occurs at lower power levels.

The loudspeaker according to the invention is very suitable for automotive applications. Most new cars have air-conditioning systems, whereby the air supplied via the ventilation shaft or shafts for cooling the driver of the loudspeaker has a nearly constant cooling temperature being the temperature in the car cabin. In this way the loudspeaker is cooled, during use of the car and loudspeaker, very effectively. Low environment temperature has a negative influence on the performance of drivers, too. In wintertime the cold loudspeaker is warmed up, during use of the car and loudspeaker, very fast to the temperature, normally about 20 degrees, in the car cabin, which results in a better performance of the speaker. In home applications an efficient cooling is guaranteed because the air supplied for cooling is coming from the front of the loudspeaker, where there is an ambient temperature of normally about 20 degrees.

In order to get a more or less homogeneous cooling of the magnet system it is preferred to provide several ventilation holes, preferably located at regular distances from each other. In such embodiment it is also preferred to provide several shafts located at regular distances from each other.

In a practical embodiment of the loudspeaker according to the invention the voice coil is provided on a cylindrical support secured to the diaphragm, which support is connected to the chassis by means of a flexible centering element, also called spider. Preferably, the support is coved by a dust cap at its front side. In this context it is noted that the frequency response of the loudspeaker may be lightly influenced by the shape and the length of the applied ventilation shaft or shafts, as there may be a certain acoustical short circuit between the front of the loudspeaker and the rear side of the dust cap. By tuning the shape and/or length of a ventilation shaft or shafts the frequency response of the loudspeaker can be optimized and said problem solved. The dust cover itself and acoustical damping material, if any, may also influence the frequency response and even the efficiency of the cooling process.

A preferred embodiment is characterized in that the magnet system comprises a neodymium-iron-bore magnet material. In a practical situation the loudspeaker according to the invention is accommodated in a substantially closed enclosure. Such an enclosure may be at least partly integrated with a construction part of an automotive or other device. The enclosure may be provided with a bass reflex port.

The invention also relates to an automotive device provided with one or more embodiments of the loudspeaker according to the invention.

The invention also relates to an audio and/or video and/or data recording and/or reproducing device provided with one or more embodiments of the loudspeaker according to the invention.

With reference to the claims it is noted that all possible combination of features mentioned in the claims are part of the invention.

These and other aspects of the invention are apparent from and will be elucidated with reference to the examples described hereinafter.

DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic longitudinal section of a first known loudspeaker;

Fig. 2 is a schematic longitudinal section of a second known loudspeaker;

Fig. 3 is a graph relating to the loudspeakers depicted in Fig. 1, plotting the sound pressure level under two different temperature conditions;

Fig. 4 is a schematic longitudinal section of a first embodiment of the loudspeaker according to the invention;

Fig. 5 is a cross section according to V - V in Fig. 4; and

Fig. 6 is a schematic longitudinal section of a second embodiment of the loudspeaker according to the invention.

DETAILED DESCRIPTION

The loudspeaker depicted in Fig. 1 is a low-midrange speaker. The loudspeaker comprises a chassis 1 and a conical diaphragm 3 disposed within the chassis L The diaphragm has an open front part 5a and a rear part 5b disposed opposite the front part 5a. The rear part 5b is provided with a dust cap 6 which seals against dust. The loudspeaker further comprises an electromagnetic driver 5 having a magnet system 7 connected to the chassis 1 and a coil, usually called voice coil, 9 connected to the rear part 5b of the diaphragm 3. The diaphragm 3 is axially movable along a central axis A - A during energizing the voice coil 9.The voice coil 9 and the magnet system 7 cooperate magnetically with one another via an air gap 11 during operation. The diaphragm 3 is connected to the cassis 1 by means of a ring-shaped flexible connecting element 13 made e.g. of polyurethane. The connecting element 13 may have an omega-shaped cross section or any other suitable shape. The voice coil 9 is carried by a coil support 15 secured to the rear part 5b of the diaphragm and centered with regard to the chassis 1 by means of a flexible centering element, usually called spider, 17. The voice coil 9 is connected to terminals via electrical conductors. These terminals and conductors are not shown in the drawing.

The magnet system 7 comprises a permanent core magnet 19 made of neodymium-iron-bore material, and a yoke structure made of a soft-magnetic material and comprising a U-shaped yoke 21a and a disc 21b. It is noted that the air present inside the magnet system 7 is enclosed by the spider 17, the dust cap 6, the magnet 19 and the yoke parts 21a and 21b.

The loudspeaker depicted in Fig. 2 bears much resemblance to the loudspeaker of Fig. 1. For this reason corresponding parts in Figs. 1 and 2 have the same reference numerals and only the difference of the loudspeaker of Fig. 2 with respect to the loudspeaker of Fig. 1 will be discussed.

The loudspeaker depicted in Fig. 2 is provided with a magnet system 8 comprising a ring-shaped permanent magnet 20 made of neodymium-iron-bore, and a yoke structure made of a soft-magnetic material and comprising a T-shaped yoke 22a and a ring- shaped plate 22b. The air present inside the magnet system 8 is shut between the spider 17, the magnet 20 and the yoke parts 22a and 22b.

The graph shown in Fig. 3 discloses two courses Cl and C2 of the Sound Pressure Level (SPL) in a wide frequency range for the loudspeaker depicted in Fig. 1. The course Cl is measured in the condition that the neodymium magnet does not suffer from thermal compression, while the course C2 is measured in the condition that the neodymium magnet does suffer from thermal compression. The negative effect of a too high temperature in the speaker is clearly demonstrated in the graph.

In the following description the same reference signs as used in the description of the loudspeakers of figures 1 and 2 are used for those parts which correspond to similar parts of those speakers. The embodiment of the loudspeaker according to the invention, depicted in Figures 4 and 5 is a low-midrange speaker. The embodiment comprises a chassis 1 having a front Ia, and a conical, particularly frusto-conical, diaphragm 3 disposed within the chassis JL The loudspeaker is accommodated in a housing 2, wherein the chassis is mounted to the housing 2. The diaphragm 3 has an open front part 5a and a rear part 5b disposed opposite the front part 5a. The rear part 5b is provided with a dust cap 6 which seals against dust. The loudspeaker further comprises an electromagnetic driver 5 having a magnet system 7 connected to the chassis 1 and a coil, usually called voice coil, 9 connected to the rear part 5b of the diaphragm 3. The diaphragm 3 is axially movable along a central axis A -A during energizing the voice coil 9. The voice coil 9 and the magnet system 7 cooperate magnetically with one another via an air gap 11 during operation. The diaphragm 3 is connected to the cassis 1 by means of a ring-shaped flexible connecting element 13 made e.g. of polyurethane. The connecting element 13 may have an omega-shaped cross section or any other suitable shape. The voice coil 9 is carried by a coil support 15 secured to the rear part 5b of the diaphragm and centered with regard to the chassis 1 by means of a flexible centering element, usually called spider, 17. The voice coil 9 is connected to terminals via electrical conductors. These terminals and conductors are not shown in the drawing.

The magnet system 7 comprises a permanent core magnet 19 made of neodymium- iron-bore material, and a yoke structure made of a soft-magnetic material and comprising a U-shaped yoke 21a and a disc 21b.

This embodiment is provided with an efficient means for cooling the magnet system 7. This efficient means includes one or more ventilation shafts 30 in combination with one or more ventilation holes 40. This embodiment has four ventilation shafts 30, which end with their ends 30a in four ventilation holes 40. The ventilation shafts 30 are, in this example, integrated in the chassis 1 and end with their free ends 30b in the front Ia of the chassisl and thus outside the housing 2. The ventilation holes 40 are provided in the magnet system 7, in this example in the yoke 21a thereof, and serve for making a communication between the ventilation shafts 30 and the air gap 11. The ventilation shafts 30 and holes 40 are arranged, in pairs, regularly, like the parts of a cross.. During energizing the voice coil 9, and thus during its translations and the translation movements of the membrane 3, (1) fresh air is moved into the free ends 30b of the ventilation shafts 30 according to arrow Al and reaches via the ventilation shafts 30 and ventilation holes 40 the space enclosed by the spider 17, the dust cap 6, the magnet 19 and the yoke parts 21a and 21b, and (2) air, particularly warm air, is moved from said space via the ventilation holes 40 and the shafts 30 towards the free ends 30b and reaches the open air according to arrow A2. In this way an efficient cooling of the magnet system is guaranteed.

The embodiment of the loudspeaker according to the invention as depicted in Fig. 6 bears much resemblance to the loudspeaker of Figures 4 and 5. For this reason only the difference of the embodiment of Fig. 6 with respect to the loudspeaker of Figures 4 and 5 will be discussed.

The embodiment depicted in Fig. 6 is provided with a magnet system 8 comprising a ring-shaped permanent magnet 20 made of neodymium- iron-bore, and a yoke structure made of a soft-magnetic material and comprising a T-shaped yoke 22a and a ring- shaped plate 22b. The air present inside the magnet system 8 is shut between the spider 17, the magnet 20 and the yoke parts 22a and 22b. In this example two ventilation shafts 30 are provided, which each ends with one of its ends 30a in two ventilation holes 40. The ventilation shafts 30 are, in this example, provided in the chassis 1 as ducts which end with their free ends 30b in the front Ia of the chassisl and thus outside the housing 2. The ventilation holes 40 are provided in the magnet system 7, in this example in the plate 22b thereof, and serve for making an open connection between the ventilation shafts 30 and the air gap 11. During energizing the voice coil 9, and thus during its translations and the translation movements of the membrane 3, (1) fresh air is moved into the free ends 30b of the ventilation shafts 30 according to arrow Al and reaches via the ventilation shafts 30 and ventilation holes 40 the space enclosed by the spider 17, the dust cap 6, the magnet 20 and the yoke parts 22a and 22b, and (2) air, particularly warm air, is moved from said space via the ventilation holes 40 and the shafts 30 towards the free ends 30b and reaches the open air according to arrow A2. In this way an efficient cooling of the magnet system is guaranteed. While the invention has been illustrated and described in detail in the drawings and foregoing description, illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments, for example, it is possible to apply one ventilation shaft or a set of three or more than four ventilation shafts. Instead of integrated ventilation shafts, ducts and the like, located inside or outside the chassis, may be used. Each ventilation shaft may have any desired cross section. The dimensions of the ventilation shafts are substantially determined by the dimensions of the speaker and the required cooling capacity. Optimizing is possible by tuning the ventilation shafts. Instead of a cone-shaped diaphragm a flat, curved or otherwise shaped diaphragm or membrane may be used successfully. Instead of a box-like housing as depicted in Fig. 4 a housing formed by a construction part of an automotive or other device, such as a consumer electronics apparatus, may be used for accommodating the loudspeaker according to the invention. Other variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the description and the claims. In the Claims and the description the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. Any reference sign in the Claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A loudspeaker comprising: a chassis having a front, a diaphragm movably suspended from the chassis, and an electromagnetic driver for driving the diaphragm with regard to the chassis, which driver includes a magnet system connected to the chassis and a voice coil connected to the diaphragm to cooperate with the magnet system via an air gap, wherein at least one ventilation shaft is provided which is connected to at least one ventilation hole in the magnet system and which ends in or near the front of the chassis, wherein the at least one ventilation hole is in communication with the air gap.

2. A loudspeaker as claimed in claim 1, wherein the ventilation shaft is integrated in the chassis.

3. A loudspeaker as claimed in claim 1 or 2, wherein several ventilation holes are provided at regular distances from each other.

4. A loudspeaker as claimed in claim 1 or 2, wherein the voice coil is provided on a cylindrical support secured to the diaphragm, which support is connected to the chassis by means of a flexible centering element.

5. A loudspeaker as claimed in claim 4, wherein the support is covered by a dust cap.

6. A loudspeaker as claimed in claim 1 or 2, wherein the magnet system comprises a neodymium-iron-bore magnet.

7. A loudspeaker as claimed in claim 1 or 2, which speaker, at least during use, is accommodated in a substantially closed enclosure.

8. An automotive device provided with the loudspeaker according to any one of the claims 1 to 7.

9. An audio and/or vide and/or data recording and/or reproducing device provided with the loudspeaker according to any one of the claims 1 to 7.

10. A device as claimed in claim 8 or 9, in combination with the loudspeaker as claimed in claim 7, wherein the enclosure is at least partly integrated with a construction part of the device.