GB2147174A - Direct radiator loudspeaker - Google Patents

Abstract

A domed loudspeaker diaphragm 1 is mounted for oscillatory movement by means of a rolled suspension 9 extending radially outwardly from the region of the end, remote from the dome, of a helical voice coil 2 which drives the dome. The coil 2 works in an annular magnetic gap 3 defined between a central pole piece 4 and an outer magnet plate 5 and the suspension thus lies on the opposite side of the magnet plate from the dome so that radiation from the suspension is obstructed by the presence of the magnet plate.

Description

SPECIFICATION Direct radiator loudspeaker This invention relates to loudspeakers ofthe direct radiatortype in which the source of acoustic radiation is adorned diaphragm driven by a helical voice coil working in an annular magnetic gap defined between a central pole piece and an outer magnet plate. The domed diaphragm or dome as it is commonly known, is mounted foroscillatory movement by means of a rolled suspension which forms an extension ofthe domeand is usually formed from the same sheetof material. The dome and suspension thus lie on the same side ofthe magnet plate and a former carrying thacoil extends from the junction between the dome andthe suspension into the magnetic gap.This type of construction is more or less standard and although it has recognised disadvantages, these have been accepted as inevitable.

Since the suspension is on the same side of the magnet top plate as the dome, it is open to the air and the acoustic radiation produced by the suspension thus tends to interfere with that from the dome.

Although attempts have been made to change or eliminate the radiation from the suspension, these have not proved entirely satisfactory. In addition, since the end ofthe coil former remote from the dome is unsupported, this end ofthe coil can flex and although anymovementcan be reduced bythe inclusion of magneticfluid in the magnetic gap, such movement can also introduce acoustic irregularities.

According to the present invention, the suspension extends radially outwardly from the region ofthe end ofthe coil remote from the dome and hence lies on the opposite side ofthe magnet plate. This means not only that radiation from the suspension is obstructed by the presence ofthe magnet plate, but also since the coil is supported at one end bythe dome and at the other end bythe suspension, any flexing with consequent acoustic irregularities is virtually eliminated. Magneticfluid is preferably included in the magneticgap and thisfurther enhances the isolation ofthe suspension and prevents any radiation from it interfering with thatfrom the dome.

The voice coil may be wound on a former constituted byan extension ofthe material of the dome and the suspension may also form part ofthe same sheet of material. Alternatively, the former may be separate from the other components.

Examples of construction in accordance with the invention will now be described with reference to the accompanying drawings, in which Figure 1 is an axial sectional viewthrough a dome and magnet assembly; and Figures 2 and 3 are detailed sectional views to an enlarged scale showing alternative forms of suspension and coil former.

Turning firstto Figure 1, a dome 1 of normal construction is driven by a voice coil 2 working in an annular magentic gap 3 between a central pole piece 4 and an outer magnet plate 5 in the usual way. In the standard type of construction, the dome 1 would be carried by a suspension lying on top of the plate 5so as to be exposed to the air as already described, thus allowing acoustic interference to take place. Instead of this, however, the material of the dome 1 continues downwardly at 8 where it joins a suspension 9. The outer edge ofthe suspension is carried by a support ring 10 located within the central space of an annular permanent magnet 11. It will thus be seen that the suspension 9 is enclosed within the magnetic structure so that any acoustic radiation from the suspension is prevented from interfering with that from the dome 1.In order to guard against even a small amount of radiation escaping through the gap 3, this isfilled with magneticfluid 12, the portion ofwhich lying within the dome 1 is injected subsequent to assembly through a passage 13 passing through the pole piece 4. The pole piece 4 is made hollowforthis purpose and is subsequently closed by a sealing plug 14. Foreign matter is prevented from entering the exposed magnetic fluid by an acoustically transparent dust cover 16.

in the construction shown in Figure 1, the dome 1, the portion 8 and the suspension 9 are formed from a single sheet of material such aspolyamideorimpre- gnated cloth.This is not essential, however, and these components can be formed separately if required. The coil 2 is wound on a separate former 15which is fitted over and secured to the part 8, thus providing greater flexibility in the construction. It is, however, also possible forthe coil to be wound directly on the part 8 as will be described in more detail with reference to Figure 3. In whichever way the coil 2 is fitted, it is supported at both ends, i.e. atthe upper end by the dome 1 andatthelowerend bythesuspension 9, so that any possibility of flexing is virtually eliminated.

The enlarged detailed view of Figure 2 makes it clear thattheformer 15 is separate from the part 8 and also illustrates an alternative form of multi-roll suspension shown as 9A. Figure 3 shows the coil 2 wound directly on the part8 without any separate former, so that the part8 itself constitutes the former. The suspension 9 is supported in the same manner as shown in Figure 1, and again the dome 1, the part 8 and the suspension 9 are formed from a single sheet of material.

1. A loudspeaker of the direct radiator type comprising a domed diaphragm mounted for oscillatory movement by means of a rolled suspension and driven by a helical voice coil connected at one end to the dome and working in an annular magnetic gap defined between a central pole piece and an outer magnet plate, and in which the suspension extends radiallyoutwardlyfromthe region of the end of the coil remote from the dome, so as to lie on the opposite side ofthe magnet plate from the dome.

2. A loudspeaker according to claim 1 in which the voice coil is wound on aformerconstituted byan extension ofthe material ofthe dome.

3. A loudspeaker according to claim 2, in which the dome, the former and the suspension are formed from a single sheet of material.

4. A loudspeaker according to any one ofthe preceding claims and including magnetic fluid in the gap between the central pole piece and the outer magnetic plate.

5. A loudspeaker of the direct radiatortype comprising a domed diaphragm mountedforoscillatory

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Direct radiator loudspeaker This invention relates to loudspeakers ofthe direct radiatortype in which the source of acoustic radiation is adorned diaphragm driven by a helical voice coil working in an annular magnetic gap defined between a central pole piece and an outer magnet plate. The domed diaphragm or dome as it is commonly known, is mounted foroscillatory movement by means of a rolled suspension which forms an extension ofthe domeand is usually formed from the same sheetof material. The dome and suspension thus lie on the same side ofthe magnet plate and a former carrying thacoil extends from the junction between the dome andthe suspension into the magnetic gap.This type of construction is more or less standard and although it has recognised disadvantages, these have been accepted as inevitable. Since the suspension is on the same side of the magnet top plate as the dome, it is open to the air and the acoustic radiation produced by the suspension thus tends to interfere with that from the dome. Although attempts have been made to change or eliminate the radiation from the suspension, these have not proved entirely satisfactory. In addition, since the end ofthe coil former remote from the dome is unsupported, this end ofthe coil can flex and although anymovementcan be reduced bythe inclusion of magneticfluid in the magnetic gap, such movement can also introduce acoustic irregularities. According to the present invention, the suspension extends radially outwardly from the region ofthe end ofthe coil remote from the dome and hence lies on the opposite side ofthe magnet plate. This means not only that radiation from the suspension is obstructed by the presence ofthe magnet plate, but also since the coil is supported at one end bythe dome and at the other end bythe suspension, any flexing with consequent acoustic irregularities is virtually eliminated. Magneticfluid is preferably included in the magneticgap and thisfurther enhances the isolation ofthe suspension and prevents any radiation from it interfering with thatfrom the dome. The voice coil may be wound on a former constituted byan extension ofthe material of the dome and the suspension may also form part ofthe same sheet of material. Alternatively, the former may be separate from the other components. Examples of construction in accordance with the invention will now be described with reference to the accompanying drawings, in which Figure 1 is an axial sectional viewthrough a dome and magnet assembly; and Figures 2 and 3 are detailed sectional views to an enlarged scale showing alternative forms of suspension and coil former. Turning firstto Figure 1, a dome 1 of normal construction is driven by a voice coil 2 working in an annular magentic gap 3 between a central pole piece 4 and an outer magnet plate 5 in the usual way. In the standard type of construction, the dome 1 would be carried by a suspension lying on top of the plate 5so as to be exposed to the air as already described, thus allowing acoustic interference to take place. Instead of this, however, the material of the dome 1 continues downwardly at 8 where it joins a suspension 9. The outer edge ofthe suspension is carried by a support ring 10 located within the central space of an annular permanent magnet 11. It will thus be seen that the suspension 9 is enclosed within the magnetic structure so that any acoustic radiation from the suspension is prevented from interfering with that from the dome 1.In order to guard against even a small amount of radiation escaping through the gap 3, this isfilled with magneticfluid 12, the portion ofwhich lying within the dome 1 is injected subsequent to assembly through a passage 13 passing through the pole piece 4. The pole piece 4 is made hollowforthis purpose and is subsequently closed by a sealing plug 14. Foreign matter is prevented from entering the exposed magnetic fluid by an acoustically transparent dust cover 16. in the construction shown in Figure 1, the dome 1, the portion 8 and the suspension 9 are formed from a single sheet of material such aspolyamideorimpre- gnated cloth.This is not essential, however, and these components can be formed separately if required. The coil 2 is wound on a separate former 15which is fitted over and secured to the part 8, thus providing greater flexibility in the construction. It is, however, also possible forthe coil to be wound directly on the part 8 as will be described in more detail with reference to Figure 3. In whichever way the coil 2 is fitted, it is supported at both ends, i.e. atthe upper end by the dome 1 andatthelowerend bythesuspension 9, so that any possibility of flexing is virtually eliminated. The enlarged detailed view of Figure 2 makes it clear thattheformer 15 is separate from the part 8 and also illustrates an alternative form of multi-roll suspension shown as 9A. Figure 3 shows the coil 2 wound directly on the part8 without any separate former, so that the part8 itself constitutes the former. The suspension 9 is supported in the same manner as shown in Figure 1, and again the dome 1, the part 8 and the suspension 9 are formed from a single sheet of material. CLAIMS

1. A loudspeaker of the direct radiator type comprising a domed diaphragm mounted for oscillatory movement by means of a rolled suspension and driven by a helical voice coil connected at one end to the dome and working in an annular magnetic gap defined between a central pole piece and an outer magnet plate, and in which the suspension extends radiallyoutwardlyfromthe region of the end of the coil remote from the dome, so as to lie on the opposite side ofthe magnet plate from the dome.

2. A loudspeaker according to claim 1 in which the voice coil is wound on aformerconstituted byan extension ofthe material ofthe dome.

3. A loudspeaker according to claim 2, in which the dome, the former and the suspension are formed from a single sheet of material.

4. A loudspeaker according to any one ofthe preceding claims and including magnetic fluid in the gap between the central pole piece and the outer magnetic plate.

5. A loudspeaker of the direct radiatortype comprising a domed diaphragm mountedforoscillatory movement substantially as described and as illustrated with reference to any Figure of the accompanying drawings.