GB2251355A

GB2251355A - Loudspeaker having multiple voice coils

Info

Publication number: GB2251355A
Application number: GB9123833A
Authority: GB
Inventors: Roger Neal Walton; Timothy Richard Nind
Original assignee: Electro Acoustic Industries Ltd
Current assignee: Harman Motive Ltd
Priority date: 1990-11-17
Filing date: 1991-11-08
Publication date: 1992-07-01
Also published as: GB9025029D0; GB9123833D0

Abstract

A loudspeaker has an annular magnet 11 disposed between a yoke 12 and an annular front plate 13. The yoke 12 has a pole 15 extending into the openings in the magnet 11 and the front plate 13 and defining a gap with the front plate 13. A supporting end 20 of a diaphragm cone 24 is suspended in the gap and carries a plurality of voice coils 30, 31 arranged to receive a signal from a corresponding amplifier output. Each voice coil 30, 31 is connected to a separate amplifier output from any other voice coil so that either each voice coil may receive the same signal from its corresponding amplifier output as the or each other voice coil to boost output or dissimilar signals are applied to provide simultaneous different outputs. <IMAGE>

Description

LOUDSPEAKER This invention relates to a loudspeaker particularly, but not exclusively for use in an automotive audio system.

It is known to provide loudspeakers for use in vehicles in which a voice coil for carrying an amplified signal is wound over the end of a loudspeaker cone lying adjacent a magnet. Such vehicle loudspeakers are usually connected to a standard voltage vehicle battery, and voice coils of approximately 4 Ohms impedance are typically provided within the loudspeaker.

An electronic chip, used to amplify the signal into the voice coil, produces a somewhat limited maximum output into such a loudspeaker.

It has been found that loudspeakers having a greater maximum power output than the current limit for loudspeakers using the standard voltage, are becoming increasingly popular. This has recently been achieved by boosting the voltage supply into the voice coil. However, it has been found necessary to use an invertor and rectifier system to boost the standard voltage, which can prove to be an expensive and inconvenient system.

It is an object of the present invention to provide an improved loudspeaker which alleviates these problems.

According to the present invention, there is provided a loudspeaker comprising a plurality of voice coils. Surprisingly, the use of a number of voice coils, preferably two, is feasible spatially and enables a multiple power output to be produced in a very simple manner.

More particularly, according to the preferred form of the invention, there is provided a loudspeaker comprising a magnet, a support and a plurality of voice coils carried by the support, the voice coils being electrically separate from one another and each having respective connection means. Preferably, support comprises an end portion of a diaphragm cone and the loudspeaker includes a plurality of amplifiers, the connection means of each voice coil being connected to a separate amplifier output from any other voice coil.

Preferably, each amplifier output includes an amplifier chip. Conveniently, each voice coil may receive the same signal from its corresponding amplifier output as the or each other voice coil.

Using this arrangement, two or more amplifier signals can excite the same diaphragm cone independently. If each voice coil carries the same signal, the power output into the loudspeaker is increased to substantially a multiple of the power output into a single coil, the multiple being the number of voice coils used and each coil being supplied by the standard voltage. This provides a particularly convenient and straight forward method of increasing the power supplied to a loudspeaker. For example, if two voice coils are provided, each capable of producing, say, 20W of power, the power into the loudspeaker is effectively doubled to about 40W.

Alternatively, each voice coil may be excited by different signals. For example, left and right hand stereophonic signals may be combined to produce a monophonic signal. Such a monophonic signal is often desirable when using sub-woofer speakers which reproduce very low frequencies.

Furthermore, an additional voice coil may be used to transmit a signal substantially unrelated to the signal transmitted by a first voice coil.

This is particularly useful, for example, in transmitting road traffic information or for noise cancellation in vehicles.

Preferably, an outer voice coil is wound over an inner voice coil, thereby providing a compact and effective two coil arrangement.

According to a further aspect of the invention, a loudspeaker comprises a magnet assembly including a magnet disposed between a yoke and a front plate, both of ferromagnetic material, an opening in each of the magnet and the front plate, the yoke including a pole portion extending through the openings in the magnet and the front plate and defining a gap with the front plate, a chassis connected to the magnet assembly, support means suspended within the gap from the chassis, a diaphragm connected to the support means and the chassis, and first and second voice coils wound onto the support means so as to lie within the gap, each voice coil being connected to a separate terminal whereby, when current passes through the voice coils magnetic fluxes are set up in the pole portion and the front plate which move the support means and the diaphragm connected thereto to produce sound in accordance with the signal inputs.

The invention also includes a vehicle including at least one loudspeaker comprising a plurality of voice coils, amplifier means connected to each voice coil, and a power source for supplying voltage to each voice coil whereby, either the power output of the loudspeaker is increased by a multiple according to the number of voice coils by exciting each voice coil with the same signal, or each voice coil may be excited by different signals for simultaneous reproduction.

A loudspeaker will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-section through a loudspeaker in accordance with the invention, showing, in a schematic manner, connections with two amplifier chips; and, Figure 2 is a schematic cross-section through I-I of part of the loudspeaker shown in Figure 1.

The loudspeaker has a magnet ring (11) having a yoke (12) and an annular front plate (13) bonded to the magnet ring (11). The plate (13) and yoke (12) are formed of ferromagnetic materia.

The yoke (12) comprises a disc-like base (14) having a cylindrical pole (15) extending from the centre thereof. The pole (15) extends through a cylindrical space (16) defined by the openings in the annular plate (13) and magnet ring (11). The pole (15) lies concentrically within the space (16) to define an annular gap. A front surface (17) of the pole (15) lies substantially co-planar with an outer surface (18) of the plate (13).

A hollow cylindrical former (20) is arranged to extend concentrically over a free end of the pole (15) and to lie partly within the space (16).

An annular air grip (21) is defined between the former (20) and the pole (15).

A substantially frusto-conical chassis (22) is attached to the outer surface (18) of the plate (13). The former (20) is secured to the chassis (22) by means of a lower suspension (23).

A frusto-conicai diaphragm (24) is bonded centrally over the former (20) and is attached to the chassis (22) by a flexible surround (25) adjacent their outer rims (26,27). The diaphragm (24) is formed of paper.

A first voice coil (30) is wound over the former (20) and lies within the space (16). A second voice coil (31) is wound over the first voice coil (30). Each voice coil is connected to a separate terminal (32,33) by flexible braid wires (34,35).

The connections between the braid wires (34,35) and each voice coil (30,31) are shown clearly in Figure 2. The terminals (32,33) connect each voice coil (30,31) with first and second amplifier chips (36,37).

A part-spherical dustcap (38) may be provided over the open end of the wire coils (30,31), bonded to either the former (20) or the diaphragm (24) to prevent unwanted particles entering the magnetic gap.

In use, the magnet ring (11) causes magnetic fluxes of opposite polarities to be set up in pole (15) and plate (13). This provides a radial magnetic field between pole (15) and plate (13).

When an alternating current passes through the voice coils, magnetic forces are set which move the diaphragm (24) to produce sound in accordance with the electrical signal input.

A vehicle battery (not shown) supplies a standard vehicle voltage into each amplifier chip (36,37) enabling each voice coil (30,31) to provide a power output substantially the same as a conventional single coil loudspeaker. Hence, if first and second chips (36,37) transmit the same signal to voice coils (30,31) the power output of the loudspeaker is substantially twice the volume that is achieved using the conventional single coil loudspeaker but using the same unboosted vehicle battery voltage.

The terminals (32,33) may be connected to separate amplifier chips as required to enable simultaneous reproduction of similar or dissimilar sound channels.

While a loudspeaker having two voice coils has been described herein, it should be appreciated that a loudspeaker having three or more coils could be used as appropriate.

The front plate (13) may be formed of iron or steel, both of which are ferromagnetic. The diaphragm (24) may also be formed of any lightweight material such as plastics or aluminium alloy.

It would be noted that the amplifier chips may also be built around and be part of the loudspeaker itself. Such a loudspeaker requires four external wires to operate: one wire for the 12V supply, one wire to carry a signal to switch the amplifier on, and two wires to carry a low level signal to be amplified locally.

Claims

1. A loudspeaker comprising a plurality of voice coils.

2. A loudspeaker according to claim 1, wherein the number of voice coils is two.

3. A loudspeaker comprising a magnet, a support and a plurality of voice coils carried by the support, the voice coil being electrically separate from one another and each having respective connection means.

4. A loudspeaker according to claim 3, comprising a plurality of amplifiers, the connection means of each voice coil being connected to a separate amplifier output from any other voice coil.

5. A loudspeaker according to claim 4, wherein each amplifier output includes an amplifier chip.

6. A loudspeaker according to claim 4 or 5, wherein each voice coil is arranged to receive the same signal from its corresponding amplifier output as the or each other voice coil.

7. A loudspeaker according to any one of claims 3 to 6, wherein the voice coils each comprise two layers of wire windings on a tubular support.

8. a loudspeaker according to claim 7, wherein an outer wire voice coil is wound over an inner wire voice coil on the tubular support.

9. A loudspeaker according to any of the preceding claims, wherein the number of voice coils is X each capable of producing Y watts of power, the voice coils each carry the same signal, and the power output of the loudspeaker comprises XY watts.

10. A loudspeaker according to any of the preceding claims, wherein each voice coil is excited by a different signal.

11. A loudspeaker comprises a magnet assembly including a magnet disposed between a yoke and a front plate both of ferromagnetic material, an opening in each of the magnet and the front plate, the yoke including a pole portion extending through the openings in the magnet and the front plate and defining a gap with the front plate, a chassis connected to the magnet assembly, support means suspended within the gap from the chassis, a diaphragm connected to the support means and the chassis, and first and second voice coils wound onto the support means so as to lie within the gap, each voice coil being connected to a separate terminal whereby, when current passes through the voice coils, magnetic fluxes are set up in the pole portion and the front plate which move the support means and the diaphragm connected thereto to produce sound in accordance with the signal inputs.

12. A loudspeaker according to claim 11, wherein the terminal of each voice coil is connected to a respective amplifier chip.

13. A vehicle including at least one loudspeaker comprising a plurality of voice coils, amplifier means connected to each voice coil, and a power source for supplying voltage to each voice coil whereby, either the power output of the loudspeaker is increased by a multiple according to the number of voice coils by exciting each voice coil with the same signal, or each voice coil may be excited by different signals for simultaneous reproduction.

14. A loudspeaker substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

15. A vehicle including at least one loudspeaker substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.