Power amplifier and loudspeaker frame integration

An integrated amplifier and speaker system includes a speaker having a motor assembly and a frame. A power stage of the amplifier is mounted in thermal communication with the motor assembly and/or the frame. Heat generated by the power stage is thereby sunk to the motor assembly and frame.

This invention relates to a combination amplifier and speaker system. More
 specifically this invention relates to a combination amplifier and speaker
 system wherein the speaker itself performs a heat sinking function for the
 amplifier.
 Conventional audio systems contemplate a separate speaker and amplifier.
 Generally, a heat sink associated with the amplifier dissipates heat
 generated by (a) power stage(s) of the amplifier. Generally, the heat sink
 is selected based upon the maximum power handling requirements of the
 power stage(s). Therefore, for (a) particular power stage(s), the heat
 sink must have a heat dissipating capability sufficient to maintain the
 temperature of the power stage(s) at or below the desired maximum
 temperature level at any output. For high power amplifiers, this separate
 heat sink often increases the cost and the bulk of the audio system. A not
 insubstantial portion of the bulk of an audio system may be traceable to
 the heat sink(s) for the power stage(s).
 An object of this invention is to integrate a speaker and an amplifier, so
 that the speaker functions as a heat sink in order to reduce the bulk
 associated with the speaker/amplifier combination.
 According to the invention, an integrated amplifier and speaker combination
 is provided. The combination comprises a speaker including a frame and
 motor assembly. A power amplifier is mounted on the motor assembly in heat
 conducting relationship therewith. The heat generated by the power
 amplifier is conducted from the power amplifier to the speaker motor
 assembly. Thus, the thermal characteristics of the motor assembly and
 frame of the loudspeaker sinks heat generated by the operation of the
 power amplifier.
 Illustratively, according to the invention the motor assembly includes a
 front plate providing a projection which extends outwardly from the motor
 assembly. The projection serves as a mounting for (a) power stage(s) of
 the power amplifier. Heat generated by the power stage(s) is transferred
 through the projection, the front plate, the magnet and the back plate of
 the motor assembly and the frame, all of which are coupled together in
 heat conducting relationship with each other. Frequently, an electrical
 insulator will be provided between the power stage(s) and the projection
 to isolate, for example, the case of the power stage(s) electrically from
 the speaker.
 A heat transfer bracket can be positioned between the motor assembly and
 the power stage(s) in heat conducting relationship with both. The bracket
 permits electrical isolation to be effected either between the power
 stage(s) and the bracket or between the bracket and the motor assembly, or
 both, at the circuit designer's option. The bracket also provides
 flexibility in mounting orientations of the power stage(s) with respect to
 the speaker. The bracket may also provide a heat spreading function.
 According to an illustrative embodiment of the invention, the motor
 assembly includes a pot-shaped shell, a permanent magnet and a core tip. A
 thermally conductive bracket is mounted in thermal communication with the
 pot-shaped shell. The power stage is mounted in thermal communication with
 the bracket.
 Illustratively, a thermally conductive material is interposed between the
 bracket and the pot-shaped shell to promote thermal communication between
 the bracket and the pot-shaped shell.

In the descriptions of illustrated embodiments that follow, the same
 reference numbers have been used to refer to those elements of each
 embodiment which perform the same or similar functions.
 Referring to FIG. 1, an amplifier and speaker combination includes a
 speaker 9 having a supporting frame 10 and a motor assembly comprising a
 backplate/center pole 12, a permanent magnet 13, and a front plate 14
 providing a substantially uniform magnetic field across an air gap 15. A
 voice coil former 16 supports a voice coil 17 in the magnetic field.
 Current related to the program material to be transduced by the speaker 9
 drives the voice coil 17, causing it to reciprocate axially in the air gap
 15 in a known manner. A cone 18 attached at its apex to an end of the coil
 former 16 lying outside the motor assembly is coupled by a surround 19 at
 its outer perimeter to the frame 10. A spider 20 is coupled at its outer
 perimeter to the frame 10. The spider 20 includes a central opening 22 to
 which the voice coil former 16 is attached. The suspension including the
 surround 19 and spider 20 constrains the voice coil 17 to reciprocate
 axially in the air gap 15.
 A typical configuration for completing the electrical connection between
 the loudspeaker terminals 24, 25 and the voice coil wires 26, 27 is
 illustrated in FIG. 1. The voice coil wires 26, 27 are dressed against the
 side of the coil former 16, and pass through central opening 22 and the
 intersection of the coil former 16 and the apex of the cone 18. Wires 26,
 27 are then dressed across the face 32 of the cone 18 to the points 28, 29
 on the face of the cone 18 where they are connected to the flexible
 conductors 30, 31. Connections 28, 29 are made by any of a number of
 available techniques. The coil wires 26, 27 typically are fixed to the
 face 32 of the cone 18 with (an) electrically non-conduction adhesive(s)
 35.
 Referring to FIG. 1, a typical power amplifier and speaker combination
 includes a printed circuit board 34 and one or more power stages 36. The
 power stage(s) 36 is(are) electrically connected by wires 38, 39 to the
 printed circuit board 34. The case 40 of a power stage 36 may also act as
 a terminal of stage 36, supplying, for example, non-zero operating
 potential to power stage 36. It is contemplated that a very wide variety
 of power amplifiers typically used in audio systems may be used in
 accordance with the invention.
 The power stage 36 is mounted on the front plate 14 of the motor assembly.
 Illustratively, the front plate 14 is fixed, for example, by (a) suitable
 adhesive(s) in a magnetic circuit and in thermally and electrically
 conductive relation with the permanent magnet 13 and backplate 12. A
 projection 42 is provided on the front plate 14. The power stage 36 is
 secured on the projection 42 in heat conducting relation with front plate
 14. An electrical insulator 44 which is a thermal conductor is interposed
 between the power stage 36 and front plate 14 to isolate the power stage
 36 electrically from the motor 12, 13, 14 and speaker frame 10 while
 permitting heat flow across insulator 44. A suitable material would be a
 thin mica sheet. This insulator 44 is often necessary because, as
 previously noted, the case 40 of power stage 36 may be at some non-zero
 voltage with respect to speaker 9 during power amplifier operation. It is
 understood that the insulator 44 may be selected from a wide variety of
 materials commonly used in electronic circuits, so long as the insulator
 does not significantly inhibit thermal conduction therethrough. Thermally
 conductive paste-like compounds also are frequently spread between the
 adjacent surfaces of stage 36 and insulator 44 and insulator 44 and front
 plate 14 to ensure intimate contact between these components and thereby
 enhance heat flow across these junctions.
 During operation of the power amplifier and speaker combination, the power
 stage(s) 36 of the amplifier generate(s) heat. This heat must be
 dissipated from the power stage(s) 36 in order to maintain the temperature
 of the power stage(s) 36 within a predetermined safe operating temperature
 range. To hold the temperature of the power stage(s) 36 within the safe
 operating temperature range, the power stage(s) 36 is(are) in heat
 conducting relationship with the front plate 14 of the motor assembly 12,
 13, 14, and, by virtue of this, with the whole speaker motor assembly and
 speaker frame 10. Front plate 14 is formed to sink the heat from the power
 stage(s) 36 into the motor assembly 12, 1314 and, where the frame 10 is
 constructed from a thermally conductive material, such as, for example,
 stamped steel, into frame 10. Thus, heat generated by the power stage(s)
 36 flows through the projection 42 of the front plate 14 and thereby into
 the motor assembly 12, 13, 14 and frame 10. In this manner, heat produced
 by operation of the power stage(s) 36 is effectively dissipated by the
 entire motor assembly 12, 13, 14 and frame 10 of the integrated speaker
 and amplifier system.
 FIG. 2 illustrates another integrated speaker and amplifier system that
 includes a motor assembly having a thermally conductive bracket 46 mounted
 on the front plate 14. Illustratively, the bracket 46 is mounted on the
 projection 42 of the front plate 14 and the power stage(s) 36 is(are)
 mounted on the bracket 46. The illustrated bracket 46 is L-shaped and may
 extend over the perimetrally outer extent of the projection 42. However,
 it is understood that the bracket 46 may take on a wide variety of shapes
 and sizes to accommodate various orientations of the amplifier with
 respect to the speaker 9 in accordance with the invention so long as
 bracket 46 promotes heat flow between the power stage(s) 36 and the motor
 assembly 12, 13, 14 and frame 10.
 As illustrated in FIG. 2, an electrical insulator 44 which is thermally
 conductive is interposed between the power stage 36 and the bracket 46 to
 isolate the power stage 36 electrically from the motor assembly 12, 13, 14
 and frame 10 of the speaker. Illustratively, the printed circuit board 34
 is also mounted on the bracket 46. Therefore, an electrical insulator 48,
 which ordinarily will also be thermally conductive, can also be provided
 between the bracket 46 and the printed circuit board 34 to isolate any
 circuit patterns on the printed circuit board 34 electrically from contact
 with bracket 46.
 FIG. 3 illustrates another configuration wherein the frame 10 is
 constructed from an electrically and thermally conductive material such as
 the previously mentioned stamped steel. A bracket 46' provided on frame 10
 permits mounting of power stage(s) 36 to frame 10. Insulator 44 permits
 heat flow from power stage(s) 36 via insulator 44 and bracket 46' to frame
 10 and motor assembly 12, 13, 14 to sink heat generated by the operation
 of power stage(s) 36.
 In the embodiment illustrated in FIG. 4, a pot shell 50 incorporates the
 functions of the front plate and back plate, other than the center pole.
 The center pole is provided by a permanent magnet 52 and a core tip 54.
 The air gap 15 is defined between the radially inner surface of the pot
 shell 50 and the radially outer surface of the core tip 54. The bracket
 46" is attached to the back surface of the pot shell 50. Illustratively,
 all of the components 50, 52, 54 of the motor assembly and the bracket 46"
 can be joined by (a) threaded fastener(s), not shown. A thermally
 conductive compound can be applied to the abutting surfaces of pot shell
 50 and bracket 46" to ensure good thermal contact between these two
 components of the assembled speaker 9.