EP0453130A2

EP0453130A2 - Inductively activated loudspeaker with conductive tube

Info

Publication number: EP0453130A2
Application number: EP91302945A
Authority: EP
Inventors: Paul Wilbur Klipsch; James Roy Hunter
Original assignee: KLIPSCH AND ASSOCIATES Inc
Current assignee: KLIPSCH AND ASSOCIATES Inc
Priority date: 1990-04-18
Filing date: 1991-04-04
Publication date: 1991-10-23
Also published as: EP0453130A3; CA2040092A1

Abstract

An inductively activated loudspeaker produces sound by inducing an oscillating current in a shorted turn conductive tube that is positioned within a focused magnetic field. The loudspeaker includes an electrically excitable stationary coil positioned within the magnetic field and in inductive relation to the conductive cylinder. The oscillation of current within the stationary coil induces a corresponding oscillating current in the cylinder, which causes the cylinder to physically oscillate within the defined magnetic field. The resultant vibratory movement of the diaphragm, upon which the cylinder is mounted, has the effect of creating sound. Also disclosed is a combined stationary coil and outer pole assembly with internalized heat sinking, and which separably attaches to the remainder of the magnetic assembly of the loudspeaker.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to loudspeakers. More particularly, this invention relates to inductively activated loudspeakers wherein the sound producing movement of a diaphragm is created by the inductive effects of an oscillating current within a coil circuit.
Inductively activated loudspeakers have been in existence for quite some time. For instance, U.S. Patent No. 1,743,749 issued to Arkell, discloses a moving coil loudspeaker arrangement that includes a short circuited winding (comprised of two series connected coils) which is mounted on a diaphragm and in inductive relation to a fixed coil. The fixed coil is supplied with oscillating current which induces a current in the short circuited winding, thereby causing sympathetic movement of the diaphragm to produce sound.
Still another inductively activated moving coil loudspeaker is disclosed in British Patent to Chapman (GB 0641651). Chapman describes a system in which alternating currents of sonic frequency that are desired to be reproduced are fed into a primary voice coil which vibrates in a magnetic gap to drive its associated diaphragm. The currents which are flowing in the primary voice coil are also induced into a secondary coil, which is short circuited or closed through an external circuit, thereby causing the secondary voice coil and its associated diaphragm to also vibrate.
Other examples of moving coil inductance speakers are shown in U.S. Patent No. 4,201,886 issued to Nagel, and U.S. Patent No. 4,295,011 issued to Hathaway. These, and other similar prior art moving coil loudspeakers, generally require the use of a coil of wire which is wound about the inner end of the diaphragm.

SUMMARY OF THE INVENTION

The present invention generally provides a new and unique inductance loudspeaker with improved design characteristics and acoustical properties. According to one embodiment, there is provided an acoustic diaphragm, a magnetic assembly, a stationary inductance coil, and a shorted turn conductive tube. The shorted turn conductive tube is mounted on the acoustic diaphragm, within the magnetic gap defined by said magnetic assembly, and in inductive relation to the stationary inductance coil. Inductive activation of the shorted turn conductive tube, caused by the oscillation of current within the stationary coil, has the effect of causing the shorted turn conductive tube to move within the defined magnetic field. The resultant vibratory movement of the diaphragm, upon which the shorted turn conductive tube is mounted, has the effect of creating sound.
One object of the present invention is to provide a new and improved loudspeaker, with improved input impedance characteristics.
Another object of the present invention is to provide a loudspeaker which has a reduced load upon the movement of the diaphragm.
Still another object of the present invention is to provide a loudspeaker which is mechanically stronger and thus more resistant to physical destruction.
Another object of the present invention is to provide a loudspeaker that allows for direct heat sinking of the input signal coil.
A further object of the present invention is to provide a loudspeaker that has increased primary winding input power capacity.
Another object of the present invention is to provide a loudspeaker which does not require a complicated crossover network design.
A further object of the present invention is to provide a loudspeaker that has a non-resonant input impedance, as seen by the amplifier at the loudspeaker terminals, and which therefore provides a near-ideal load for passive electrical filters.
Other objects and benefits of the present invention can be appreciated from a review of following written description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view in cross section of a direct radiating loudspeaker, according to one embodiment of the present invention.
FIG. 2 is a side elevational view in cross section of a second embodiment of the present invention.
FIG. 3 is a side elevational view in cross section of a third embodiment of the present invention.
FIG. 4 is a fragmentary side elevational view in cross section of a compression driver loudspeaker, incorporating the first above embodiment of the present invention.
FIG. 5 is a fragmentary side elevational view in cross section of another alternative embodiment, incorporating a replaceable stationary coil and outer pole assembly with internalized heat sinking.
FIG. 5A is a fragmentary side elevational view of the coil assembly of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated devices, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
Referring now to the drawings, the invention will now be described, with reference to FIGS. 1-3, in relation to direct radiating speakers. In FIGS. 4 and 5, the description of the invention will be made in the context of a compression driver speaker.
Referring now to FIG. 1, there is illustrated a loudspeaker 10 which embodies the present invention. The loudspeaker in general comprises acoustic diaphragm 11, frame 12, suspension spider 13, dust cap 14, surround 15, stationary coil 16, conductive tube 17 and magnetic assembly 18.
Diaphragm 11 is substantially frusto-conically shaped and its wide end is attached to the front end of frame 12 by surround 15. The function of surround 15 is to allow relatively free axial displacement of the diaphragm while preventing its lateral displacement. The back end of frame 12 is secured to the front end of magnetic assembly 18 by spider 13, which is concentrically corrugated and which also functions to allow relatively free axial movement or piston movement of diaphragm 11 while offering resistance to lateral displacement.
Magnetic assembly 18 produces a focused magnetic field and includes annular magnet 19, an annular soft iron front ring 22, an annular soft iron back end plate 23 and an iron core 24. Back end plate 23 and iron core 24 may be formed as one piece. Magnet 19 has a north pole face 20 and a south pole face 21. Magnet 19 can be formed from a variety of suitable materials, such as ceramic, and may include various magnetic materials, such as barium or strontium ferrite. The front end portion 28 of iron core 24 defines a focused magnetic field within gap 26 between the front end portion 28 of iron core 24 and ring 22. Dust cap 14 is provided to keep dust and other particles out of gap 26.
Stationary coil 16, wound about the front end portion 28 of core 24, is positioned within the magnetic field created in gap 26, and is also in inductive relation to conductive tube 17. The wire used to form coil 16 may be made of low resistivity copper or silver. Conductive tube 17 is made of aluminum and is rigidly attached at one of its ends to the inner end of diaphragm 11 while its other end extends rearwardly into gap 26 defined by magnetic assembly 18.
When an oscillating signal is applied to coil 16, the inductive relationship between coil 16 and tube 17 causes a corresponding oscillating current to be induced in tube 17. The magnetic effects of the induced current in tube 17 react with the relatively strong magnetic field produced by magnetic assembly 18 to cause tube 17, and thus diaphragm 11, to physically oscillate, thereby producing audible sound.
In another embodiment of the present invention, loudspeaker 40, shown in FIG. 2, generally includes acoustic diaphragm 41, frame 42, suspension spider 43, dust cap 44, surround 45, stationary coil 46, conductive tube 47 and magnetic assembly 48. Magnetic assembly 48, which produces a focused magnetic field, includes annular magnet 49, annular soft iron front end ring 52, annular soft iron back end plate 53 and iron core 54. Magnet 49 has a north pole face 50 and a south pole face 51. Magnetic assembly 48 defines a focused magnetic field within gap 56 between iron core 54 and ring 52. The alternate embodiment of the loudspeaker of the present invention shown in FIG. 2 is identical to the embodiment shown in FIG. 1 in all other respects except that in the embodiment shown in FIG. 2,stationary coil 46 is positioned directly adjacent and on the interior surface of ring 52.
Still another embodiment of the present invention is shown in FIG. 3 in which loudspeaker 70 includes acoustic diaphragm 71, frame 72, suspension spider 73, dust cap 74, surround 75, first stationary coil 76, conductive tube 77, magnetic assembly 78 and second stationary coil 88. Magnetic assembly 78, which produces a focused magnetic field, includes annular magnet 79, annular soft iron front end ring 82, annular soft iron back end plate 83 and iron core 84. Magnet 79 has a north pole face 80 and a south pole face 81. Magnetic assembly 78 defines a focused magnetic field within gap 86 between the front end portion of iron core 84 and ring 82. This alternate embodiment of the loudspeaker of the present invention shown in FIG. 3 is identical to the embodiment shown in FIG. 1 in all other respects except that in the embodiment shown in FIG. 3, there exists a second stationary coil 88 positioned adjacent the interior surface of ring 82.
FIG. 4 illustrates the incorporation of the present invention into a compression driver loudspeaker. Loudspeaker 90 generally includes dome diaphragm with integral compliance 91, directional horn 94, phasing plug 95, stationary coil 96, conductive tube 97 and magnetic assembly 98. Magnetic assembly 98 produces a focused magnetic field and includes annular magnet 99, annular soft iron front end ring 102, annular soft iron back end plate 103 and iron core 104. Back end plate 103 and iron core 104 may be formed as one piece. Magnet 99 has a north pole face 100 and a south pole face 101. Magnetic assembly 98 defines a focused magnetic field within gap 106 between the front end portion 108 of iron core 104 and ring 102.
Stationary coil 96, wound about the front end portion 108 of core 104, is positioned within the magnetic field created in gap 106, and is also in inductive relation to conductive tube 97. Coil 96 is made of low resistivity copper or silver wire. Conductive tube 97 is made of aluminum and is rigidly attached at one of its ends to the inner end of diaphragm 91 while its other end extends rearwardly into gap 106. When an oscillating signal is applied to coil 96, the inductive relationship between coil 96 and tube 97 causes a corresponding oscillating current to be induced in tube 97. The magnetic effects of the induced current in tube 97 react with the relatively strong magnetic field produced by magnetic assembly 98 to cause tube 97, and thus diaphragm 91, to physically oscillate, thereby producing audible sound.
FIG. 5 illustrates yet another alternative embodiment of the present invention, incorporating a replaceable stationary coil and outer pole assembly 125 with internalized heat sinking. The entire loudspeaker 110 of this embodiment is not expressly described, however, the embodiment shown in FIG. 5 is identical to the embodiment shown in FIG. 4 in all other respects except that in the embodiment shown in FIG. 5, stationary coil 116 is readily removably positioned directly adjacent a removable inner portion of annular soft iron ring 122.
Loudspeaker 110 includes a readily removable stationary coil and outer pole assembly 125, which is shown in detailed view in FIG. 5A. Assembly 125 includes removable soft iron outer pole 130, heat sink 131, a pair of externally threaded studs 132 and 133, coil former 134, and stationary coil 116. Ring 122 has a pair of internally threaded openings 135 and 136 located adjacent recess 140. Assembly 125 is mountable to the inner portion of ring 122 in recess 140 by screwing studs 132 and 133 into their respective openings 135 and 136 as shown in FIGS. 5 and 5A.
Heat sink 131 is composed of cast epoxy or plastic. Formed integral as one piece with heat sink 131 is outer pole 130 and lead 117. Wire 118 extends into removable coil assembly 125 and is attached to lead 117. Wire 118 is a higher gage wire as compared to lead 117 and is shown as such in FIGS. 5 and 5A. Lead 117 is fully contained within removable coil assembly 125 in order to protect lead 117 from heat damage. Stationary coil 116 is located within a recess 119 of removable coil assembly 125. Positioned at the end of removable coil assembly 125 and adjacent conductive tube 120 is coil former 134. Coil former 134 is composed of paper or plastic and is used as a base on which coil 116 is wound. The above loudspeaker design, as shown in FIGS. 5 and 5A, facilitates field replacement of the stationary coil when it is not functioning properly due to heat damage or the like.
Generally speaking, each of the above described loudspeakers provides attendant advantages of improved mechanical strength with a reduced load upon the movement of the diaphragm. The structure needed to support a coil attached to a diaphragm, as well as the insulation of the winding in the coil itself and the adhesives used for attachment of the winding to the support structure, necessarily create an added load on the moving system of the loudspeaker. A simple conductive tube, on the other hand, is its own support structure, and does not burden the moving system with added mass. As a result, mechanical strength is improved, while at the same time, the physical load upon the diaphragm is reduced for any given electrical conductivity that may be required. Excess weight on the inner end of the diaphragm, which can cause turbulent action of the diaphragm which in turn reduces the efficiency of operation of the loudspeaker, is avoided. In addition, ferro fluids may be used with the speakers of the present invention, and the relatively smooth profile of the cylindrical members, such as 17 or 47, will result in less disruption of the fluid as the cylinder moves.
By allowing for direct heat sinking of the input signal coil to relatively massive parts, the above described loudspeaker design has the advantage of allowing for increased primary winding input power capacity. Devices which do not provide for such direct heat sinking, are limited in their ability to increase primary winding input power capacity without a corresponding cost upon the system.
Further, the described loudspeaker arrangement simplifies the effort needed to design the associated crossover network which is electrically coupled between the input of the loudspeaker (e.g. the leads of stationary coil 16) and the output of the acoustical signal source (i.e. the associated audio power amplifier). This is due to the fact that the loudspeaker has essentially a non-resonant input impedance (as seen by the amplifier at the loudspeaker terminals) which results in a near-ideal load for passive electrical filters.
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

Claims

A loudspeaker comprising:
an acoustic diaphragm;
means for producing a focused magnetic field;
an electrically excitable stationary coil; and
a shorted conductive cylinder attached to said diaphragm and positioned within said focused magnetic field and in inductive relation to said stationary coil.
The loudspeaker of claim 1 wherein said stationary coil is positioned within said focused magnetic field.
The loudspeaker of claim 1 further including a second electrically excitable stationary coil positioned in inductive relation to said conductive cylinder.
The loudspeaker of claim 3 wherein said second stationary coil is positioned within said focused magnetic field.
The loudspeaker of claim 1 wherein said means for producing a focused magnetic field includes a permanent magnet assembly.
The loudspeaker of claim 1 wherein said first stationary coil is positioned within said conductive cylinder.
The loudspeaker of claim 1 wherein said first stationary coil is positioned outside of said conductive cylinder.
The loudspeaker of claim 3 wherein said first stationary coil is positioned within said conductive cylinder and said second stationary coil is positioned outside of said conductive cylinder.
The loudspeaker of claim 5 wherein said first stationary coil is positioned on said permanent magnet assembly.
The loudspeaker of claim 4 wherein said said means for producing a focused magnetic field includes a permanent magnet assembly, and wherein second stationary coil is positioned directly thereon.
The loudspeaker of claim 1 wherein said stationary coil includes low resistivity copper or silver wire.
The loudspeaker of claim 1 wherein said stationary coil is readily replaceable.
The loudspeaker of claim 1 wherein said conductive cylinder is composed of aluminum.
A loudspeaker comprising
an acoustic diaphragm;
a magnetic assembly, said magnetic assembly defining a gap within which extends a magnetic field;
a first stationary coil; and
a shorted turn conductive tube mounted on said diaphragm and positioned within said gap and in inductive relation to said stationary coil.
The loudspeaker of claim 14 further including a second stationary coil positioned in inductive relation to said conductive tube.
The loudspeaker of claim 15 wherein said defined gap is annular in shape and in which said first and said second stationary coils are positioned within said gap.
The loudspeaker of claim 14 wherein said first stationary coil is positioned directly on a portion of said magnetic assembly.
The loudspeaker of claim 16 wherein said conductive tube is composed of aluminum.
The loudspeaker of claim 18 wherein said first stationary coil is positioned within said conductive tube and said second stationary coil is positioned outside of said conductive tube.
The loudspeaker of claim 17 wherein said first stationary coil is readily removable.