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US-12621609-B1 - Voice coil speaker with conductive cooling

US12621609B1US 12621609 B1US12621609 B1US 12621609B1US-12621609-B1

Abstract

Example embodiments provide a voice coil speaker that may comprise a speaker frame and a diaphragm connected to the speaker frame and configured to be capable of axial movement. A heat conducting coil former may be connected to the diaphragm. A pole piece and a back plate may form an annular gap and conduct magnetic flux from an axially polarized permanent magnet in a complete loop that includes the annular gap. A voice coil may be wound on the heat conducting coil former and residing in the annular gap, the magnetic flux passing through the voice coil in the radial direction, such that the voice coil produces an axial force to cause the diaphragm to produce sound. A thermal bridge may be configured to conduct heat from the heat conducting coil former to the back plate.

Inventors

  • John Miesner
  • Matthew Willey

Assignees

  • UNITED STATES OF AMERICA AS REPRESENTED BY THE SECRETARY OF THE NAVY

Dates

Publication Date
20260505
Application Date
20230616

Claims (13)

  1. 1 . A voice coil speaker comprising: a speaker frame; a diaphragm connected to the speaker frame and configured to be capable of axial movement; an axially polarized permanent magnet; a back plate; a heat conducting coil former connected to the diaphragm, and surrounded by a sleeve; a pole piece, wherein the pole piece and the back plate form an annular gap and conduct magnetic flux from the axially polarized permanent magnet in a complete loop that includes the annular gap; a voice coil wound on the heat conducting coil former and residing in the annular gap, the magnetic flux passing through the voice coil in the radial direction, such that the voice coil produces an axial force to cause the diaphragm to produce sound; and a thermal bridge configured to conduct heat from the heat conducting coil former to the back plate, wherein the heat conducting coil former includes a groove into which the voice coil is wound to ensure thermal contact between the voice coil and the heat conducting coil former, the groove being an opening within the heat conducting coil former and covered by the sleeve, such that the voice coil is enclosed within the heat conducting coil former and covered by the sleeve.
  2. 2 . The voice coil speaker of claim 1 , wherein the axial force is produced by the interaction of the voice coil with the radial magnetic field when subjected to electrical current flow, the axial force causes axial movement of the diaphragm; and the diaphragm causes alternating compression and rarefaction of the contacting air to produce the sound.
  3. 3 . The voice coil speaker of claim 1 , wherein heat is conducted radially and axially from the voice coil into the heat conducting coil former.
  4. 4 . The voice coil speaker of claim 1 , wherein the heat conducting coil former is made of material with high thermal conductivity and conducts heat from the voice coil axially to the thermal bridge.
  5. 5 . The voice coil speaker of claim 4 , wherein the material with high thermal conductivity is at least one of aluminum or copper.
  6. 6 . The voice coil speaker of claim 1 , wherein the heat conducting coil former includes a plurality of axial slits to prevent eddy currents from being induced in the heat conducting coil former by a current through the voice coil or by relative motion of the heat conducting coil former with the magnetic field in the annual gap, wherein the plurality of axial slits extend past a point of maximum travel of the heat conducting coil former in the annular gap.
  7. 7 . The voice coil speaker of claim 1 , wherein the heat conducting coil former is reinforced by the sleeve, the sleeve being made of high strength nonconducting material, the sleeve being attached with epoxy, the epoxy filling the slits in the heat conducting coil former and resulting in a hybrid structure.
  8. 8 . The voice coil speaker of claim 7 , wherein the high strength nonconducting material is at least one of glass or a carbon fiber composite.
  9. 9 . The conductively cooled voice coil speaker of claim 1 , wherein the thermal bridge comprises: top attachment bars; bottom attachment bars; and flexible copper stranded wires that join the top attachment bars and the bottom attachment bars, wherein the flexible copper stranded wires conduct heat between the top attachment bars and the bottom attachment bars.
  10. 10 . The conductively cooled voice coil speaker of claim 1 , wherein the thermal bridge comprises: a top attachment ring; a bottom attachment ring; and flexible copper stranded wires that join the top attachment ring and the bottom attachment ring, wherein the flexible copper stranded wires conduct heat between the top attachment ring and the bottom attachment ring.
  11. 11 . The conductively cooled voice coil speaker of claim 1 , wherein the thermal bridge comprises: a top attachment ring; a bottom attachment ring; and flexible copper strips that join the top attachment ring and the bottom attachment ring, wherein the flexible copper strips conduct heat between the top attachment ring and the bottom attachment ring.
  12. 12 . The conductively cooled voice coil speaker of claim 1 , wherein the voice coil is surrounded on three of four sides by the heat conducting coil former.
  13. 13 . The conductively cooled voice coil speaker of claim 6 , wherein the plurality of axial slits have the same configuration along the groove of the heat conducting former such that the plurality of axial slits are configured to surround the voice coil on three sides and are covered by the sleeve on a fourth side.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63/490,037 filed Mar. 14, 2023, titled “Voice Coil Speaker with Conductive Cooling,” incorporated herein by reference. STATEMENT OF GOVERNMENT INTEREST The following description was made in the performance of official duties by employees of the Department of the Navy, and, thus the claimed invention may be manufactured, used, licensed by or for the United States Government for governmental purposes without the payment of any royalties thereon. TECHNICAL FIELD The invention relates generally voice coil speakers. BACKGROUND Permanent magnet voice coil speakers employ a diaphragm which is vibrated by a current conducting coil that resides in a magnetic flux from one or more permanent magnets. The interaction between the current passing through the voice coil and the magnetic field causes the voice coil to oscillate in accordance with the electrical current and drive the diaphragm to produce sound. Speaker design goals are to produce a high level of audio power with low distortion (high fidelity) in a compact size. One limitation on design is that the resistance of the voice coil produces heat which affects the fidelity and must be removed to prevent damage to the voice coil and other speaker components. The current conducting coil of a voice coil speaker is typically wound onto a coil former that is made of a material with a low electrical conductivity such as paper or plastic. These materials typically have a low thermal conductivity of about 0.2 W/mK and therefore carry away little of the heat energy generated in the coil. Improved heat transfer can be realized by making the coil former from materials with a high thermal conductivity such as aluminum, with conductivity of 240 W/mk, or copper, with conductivity of 400 W/mK. Unfortunately, these materials also have a high electrical conductivity which causes two problems; the current in the coil induces a counter-current in the coil former which interacts with the magnetic field to produce forces that tend to cancel the coil forces, and the motion of the coil former relative to the magnetic field induces eddy currents in the coil former which retard the relative motion and produces heating and audio distortion. Active cooling methods have been developed including forced air flow through the gap or liquid cooling of the coil or magnets. Although these methods are effective, they tend to increase cost and weight while reducing reliability. SUMMARY OF THE INVENTION Example embodiments provide a voice coil speaker that may comprise a speaker frame and a diaphragm connected to the speaker frame and configured to be capable of axial movement. A heat conducting coil former may be connected to the diaphragm. A pole piece and a back plate may form an annular gap and conduct magnetic flux from an axially polarized permanent magnet in a complete loop that includes the annular gap. A voice coil may be wound on the heat conducting coil former and residing in the annular gap, the magnetic flux passing through the voice coil in the radial direction, such that the voice coil produces an axial force to cause the diaphragm to produce sound. A thermal bridge may be configured to conduct heat from the heat conducting coil former to the back plate. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view of the voice coil speaker illustrating the overall arrangement according to an example embodiment. FIG. 2 is a cross-sectional view of the voice coil assembly according to an example embodiment. FIG. 3 is an exploded view of the voice coil assembly according to an example embodiment. FIG. 4A is an isolated view of a thermal bridge according to a first example embodiment. FIG. 4B is an isolated view of a thermal bridge according to a second example embodiment. FIG. 4C is an isolated view of a thermal bridge according to a third example embodiment. DETAILED DESCRIPTION OF THE INVENTION In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular structures, designs, techniques, etc., in order to provide a thorough understanding of the example embodiments. However, it will be apparent to those skilled in the art that the disclosed subject matter may be practiced in other illustrative embodiments that depart from these specific details. In some instances, detailed descriptions of well-known elements and/or method are omitted so as not to obscure the description with unnecessary detail. All principles, aspects, and embodiments, as well as specific examples thereof, are intended to encompass both structural and functional equivalents of the disclosed subject matter. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future. The following description refers to a voice coil speaker apparatus. However, it should be noted that