EP1248494B1

EP1248494B1 - Cup-shaped loudspeaker armature with magnets from neodymium

Info

Publication number: EP1248494B1
Application number: EP02004928A
Authority: EP
Inventors: Tiziano Nili; Carlo Sancisi; Eleuterio Benedetti
Original assignee: Sipe Italiana Prodotti Elettromeccanici - SpA Soc; S I P E SOC IT PRODOTTI ELETTR
Current assignee: Ask Industries SpA
Priority date: 2001-03-23
Filing date: 2002-03-05
Publication date: 2009-08-26
Anticipated expiration: 2022-03-05
Also published as: EP1248494B8; ITRE20010026A0; ATE441290T1; AR032994A1; PL352984A1; EP1248494A2; PL211427B1; ITRE20010026A1; BRPI0201190B1; ES2332446T3; DE60233455D1; EP1248494A3; BR0201190A

Description

The present invention relates to a loudspeaker with magnets from neodymium.
More particularly, the present invention relates to a loudspeaker cup with magnets from neodymium, to which there may be associated upper planar plates, particularly suitable to be applied on conventional or reversed assembly loudspeakers. As is known, the metal structure that constitutes the so-called external cup of the present loudspeakers may be realized either by turning, with or without rear discharge and with or without cooling flanges, to rather high and little economical costs, or by molding or spinning. In any case, the internal metal surfaces of said cups are rather nearby the magnet, to such an extent as to short said magnet, with a subtraction of useful flow in the magnetic gap that causes the system efficiency to drop. As is known, in order to recover such efficiency, magnets having a greater diameter must be used.
Another drawback lies in that the air volume available in the inside of the magnetic circuit is modest and such as not to allow a good ventilation and an adequate cooling of the mobile bobbin.
US5687248 discloses a magnetic circuit for a low-weight loudspeaker further aiming to reduce the magnetic leakage. Such magnetic circuit provides for a cylindrical cup-shaped yoke including a bottom part and a ring part fixed on the periphery of the bottom part, with a primary neodymium magnet located over said bottom part, a central top plate over said magnet and a second thin magnet over said plate.
EP0581129 discloses a magnet system for an electroacustic transducer with a significantly increased inductance in the air gap. The system provides for a substantially cylindrical magnet pot and a neodymium discoidal magnet on the bottom thereof, a pole plate over said magnet and a further neodymium disc arranged over the pole plate to increase the inductance in said air gap.
US5987148 discloses a driver for use with a horn radiator with improved capability of dissipating heat to prevent overheating. It comprises a substantially cylindrical yoke on the bottom of which rests a neodymium magnet and a flux guiding plate superimposed on the yoke.
Object of the present invention is to eliminate the drawbacks of the prior art devices.
In its most general aspect, the present invention allow to obtain these and other purposes, as will be clear thanks to the following description, by means of a loudspeaker cup having a shape such as to create an internal chamber sufficient to comprise a remarkable volume of cooling air with wide thermal dissipation surfaces and to increase the distance between the diametric surface of the magnet and the internal surface of said cup. Therefore, object of the present invention is an assembly comprising a loudspeaker cup with a magnet from neodymium having the features defined in claim 1.
The cup of the present invention may be obtained by spinning.
The advantages achieved with the cup of the present invention lies essentially in that:

the greater distance between the diametric surface of the magnets and the internal metal wall of the cups prevents the subtraction of useful flow lines ensuing from shorts, with an evident improvement in efficiency of the loudspeakers;
- the greater air volume available and the greater development of the cup walls ensure an effective dissipation of the heat generated by the mobile bobbin in the area of the useful flow and a lower compression;
- the above conditions allow the adoption of magnets from neodymium having a smaller diameter, with a lower degree of temperature resistance and a reduced weight;
- the cups may be realized with metal sheets having a contained thickness that contributes to the overall weight reduction;
- a general construction economy, arising also from the fact that the mechanical components are realizable with high automation processes.

Other advantages lie in that, in the magnetic gap or useful flow area, the magnetic induction lines are more uniform and constant, and the magnetic induction lines outside the magnetic gap, in both the internal and external directions of the magnetic circuit, are more symmetrical. All these features cause a lower total harmonic distortion (THD) measurable at the medium and medium-low frequencies, with ensuing "cleanness" and "transparency" of the sound reproduced.
The constructive and functional characteristics of the loudspeaker cups with a magnet from neodymium of the present invention will be better understood thanks to the following description, wherein reference is made to the attached drawings which represent some embodiments reported only by way of non limiting examples, and wherein:

Figure 1 shows a section view of an example of polar plate cup to be assembled traditionally for loudspeakers with a magnet from neodymium, according to the present invention;
Figure 2 and 3 show the partial cross-section, limited with respect to the symmetry axis, of two examples of cups provided with polar plates to be assembled traditionally, for loudspeakers with a magnet from neodymium, according to the present invention;
Figures 4 and 5 show the partial cross-section, limited with respect to the symmetry axis, of two examples of cups to be assembled in a reversed manner, for loudspeakers with a magnet from neodymium, according to the present invention; and
Figures 6 and 7 shows the diagrams of THD of two loudspeakers with a classic circuit from ferrite compared with like loudspeakers with a neodymium circuit, according to the present invention.

With reference to Figure 1, one can observe that cup 1 has a convex shape, and is much more marked with respect to the configuration of the cups of a known type, whose medium diameter A is much more greater than, and spaced from, the external diameter B of magnet 2; wherein the medium diameter A is the one related to the internal wall of the cup taken in the flexion point. The substantial distance D between the diametric surface 3 of magnet 2 and the internal surface 4 of cup 1, allows to realize a toroidal chamber 5 having a high air volume useful to allow a good cooling ventilation for the mobile bobbin, and to prevent "compression" phenomena of the loudspeaker. The size of such toroidal chamber 5 depends on such difference D. Tests carried out have provided very significant results. In substantially optimal conditions, the A/B ratio was ≅ 1.7, with a field comprised between 1.4 < A/B < 1.8, wherein the efficiency on the limits decreases by ≅ 3 - 4%.
The above data are reported only by way of example, and it is evident that variations in the aforesaid values are admissible, depending on the specific requirements, without falling outside the invention scope.
Magnet 2 may be of the usual type or of a type with a reduced diameter and/or normal or lower temperature resistance.
The presence of the planar plate 6, as shown in Figures 2 and 3, allows a high thermal dispersion in the area where heat is generated, subtracting it efficiently from magnet 2. Lines 7 represent, in the direction of and towards, the thermal flow generated by the difference in temperature between the inside and the outside of the magnetic circuit. The significant distance D between the diametric surface 3 of magnet 2 and the internal surface 4 of cup 1, and the conformation of said cup, form the high air volume toroidal chamber 4 that ensures a ventilation sufficient to cool the mobile bobbin. The flow lines 8 indicate the trend of the magnetic induction lines. Lines 9 stress, instead, the trend of the useful flow, compact and substantially uniform, with minimal dispersion lines and a better shielding of the magnetic circuit.
Figure 3 shows a variant of Figure 2 of a cup with a polar plate to be conventionally assembled for loudspeakers with magnets from neodymium, wherein, besides the main magnet 2, a standby magnet 2" is provided. Both magnets are counter-polarized and allow to have a higher useful magnetic flow, and therefore a greater efficiency.
To sum up, the configurations shown in the aforesaid Figures 2 and 3 for application on loudspeakers to be conventionally assembled, provide the following advantages:

a) high efficiency due to distance D between the metal material of cup 1 and the central magnet 2,
b) magnetic induction lines uniform and constant in the area of the magnetic gap or the useful flow,
c) greater symmetry of the magnetic induction lines outside the magnetic gap, both in the internal direction and the direction external with respect to the magnetic circuit,
d) lower total harmonic distortion (THD) measurable at the medium and medium-low frequencies, with ensuing "cleanness" and "transparency" of the sound reproduced,
e) high thermal dispersion due to the presence of the polar plate that acts as a thermal radiator in the area where the heat of the mobile bobbin develops, the greater extension of the cup wall, and a greater air volume with respects to the solutions of the known art.
f) possibility of utilizing more economical neodymium magnets, with a lower degree of temperature resistance, thanks to the better thermal dispersion,
g) containment of the overall due to the use of low thickness sheets and smaller diameter neodymium magnets,
h) general economy of the circuit metal components due to the use of more economical materials and high automation processes.

In the configurations of Figures 4 and 5 showing solutions suitable for reversed assembly, cup 1' is so profiled as to generate in any case a distance D' between its internal surface 4' and the diametric surface 3' of magnet 2', for the constitution of a toroidal chamber 5', sufficiently wide to obtain the air volume necessary for a good cooling ventilation of the mobile bobbin, and to prevents said loudspeaker "compression" phenomena.
The basic characteristics remain substantially equal to those already described for the configurations for solutions suitable for conventional assembly. The flow lines 8' indicate the trend of the magnetic induction lines through the wall of cup 1'. Lines 9' stress, instead, the trend of the useful flow, compact and substantially uniform, with minimal dispersion lines and a better shielding of the magnetic circuit.
To sum up, the configurations shown in the aforesaid Figures 4 and 5, for application on reversed assembly loudspeakers, provide the following advantages:

a') high efficiency due to distance D' between the metal material of cup 1' and the central magnet 2',
b') magnetic induction lines, uniform and constant in the area of the magnetic gap or the useful flow,
c') greater symmetry of the magnetic induction lines outside the magnetic gap, both in the internal direction and the direction outside the magnetic circuit,
d') lower total harmonic distortion (THD) measurable at the medium and medium-low frequencies, with ensuing "cleanness" and "transparency" of the sound reproduced,
e') high thermal dispersion due to the presence of a high extension of the surface of the metal wall of cup 1' and a greater air volume with respect to the solutions of the known art,
f') possibility of utilizing more economical neodymium magnets, with a lower degree of temperature resistance, thanks to the better thermal dispersion,
g') containment of the overall weight due to the use of sheets having a reduced thickness and neodymium magnets of a lower diameter,
h') general economy of the circuit metal components due to the use of more economical materials and high automation processes,
i') a geometry designed to prevent shape interference in circuits for reversed loudspeakers.

Figures 6 and 7 show the results of two examples of tests carried out in mobile bobbin loudspeakers having a diameter in the range of 19-20 mm. In both cases, there are compared the harmonic distortion values (THD) that take place in a loudspeakers provided with a classic magnetic circuit from ferrite (broken curve) and in a like loudspeaker provided with a magnetic circuit from neodymium with cups according to the invention (continuous curve); the percent reduction in the harmonic distortion values obtained with the loudspeakers according to the invention are evident and substantial.
Although the invention has been described in conjunction with specific embodiments, offered for illustrative purpose only, it is evident that many alternative and variations will be apparent to those skilled in the art in the light of the foregoing description.
Accordingly, the invention is intended to embrace all of the alternatives and variants that fall within scope of the appended claims.

Claims

An assembly comprising a cup for a loudspeaker and a neodymium magnet , said cup being formed of metal sheet and having a shape with a cross section profile providing for a flexion point and a raised central portion for supporting said magnet (2, 2'), the ratio between the internal wall diameter (A, A') taken at said flexion point and the external diameter (B, B') of said magnet (2, 2') being comprised between 1.4 and 1.8 .
An assembly as claimed in claim 1, characterized in that said ratio is of about 1.7.
An assembly as claimed in claim 1 or 2, characterized in that it comprises an upper thermal radiation planar polar plate (6).
A loudspeaker cup as claimed in claims 1 to 3, characterized in that it further comprises a second magnet (2"), counter-polarized with respect to said neodymium magnet (2).