Inside-Wound Voice Coil Bobbin for Loudspeaker Thermal Management

Solution Overview

Problem

High-power, long-excursion loudspeakers face thermal and mechanical overload issues, leading to voice coil failure due to extreme excursions and heat generation, which causes the voice coil to rub against the magnetic gap, resulting in catastrophic failures.

Innovation Solution

The voice coil is wound solely on the inside surface of a cylindrical bobbin, allowing it to maintain proximity to a thermally conductive front plate without rubbing, even during thermal expansion, and the motor structure is designed with a central pole piece that projects forward to enhance thermal transfer, preventing catastrophic failures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If the voice coil is positioned close to the front plate to enhance thermal transfer, then heat dissipation is improved, but the voice coil may rub against the front plate during thermal expansion, causing catastrophic failure

Engineering Contradiction:

Improveheat dissipationVSAvoidvoice coil failure

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent inverts the conventional voice coil winding approach by winding the voice coil entirely on the inside surface of the bobbin rather than on the outside. This inversion allows the voice coil to maintain close proximity to the thermally conductive front plate for enhanced heat dissipation while the bobbin's outer surface acts as a protective barrier preventing the voice coil from rubbing against the front plate during thermal expansion.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The bobbin serves as an intermediary element between the voice coil and the front plate. By positioning the voice coil inside the bobbin and making the bobbin thermally conductive, it facilitates heat transfer from the voice coil to the front plate while simultaneously providing mechanical protection and maintaining proper spacing to prevent contact during thermal expansion.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If the voice coil is wound on the outside of the bobbin for conventional construction, then manufacturing is easier, but the voice coil cannot maintain close proximity to the front plate for effective thermal transfer

Engineering Contradiction:

Improvevoice coil windingVSAvoidthermal transfer

Core Design Contradiction:

Ease of manufactureVSTemperature

Solution Approach 1:

The patent inverts the conventional voice coil winding approach by winding the voice coil entirely on the inside surface of the bobbin rather than on the outside. This inversion allows the voice coil to maintain close proximity to the thermally conductive front plate for enhanced heat dissipation while the bobbin's outer surface acts as a protective barrier preventing the voice coil from rubbing against the front plate during thermal expansion.

Inventive Principle:

Principle #13The other way round (Inversion)

3Stress or pressure

If the voice coil is allowed to expand freely during thermal expansion, then thermal stress is reduced, but the voice coil rubs against the magnetic gap, causing catastrophic failure

Engineering Contradiction:

Improvethermal stressVSAvoidcatastrophic failure

Core Design Contradiction:

Stress or pressureVSReliability

Solution Approach 1:

The bobbin serves as an intermediary element between the voice coil and the front plate. By positioning the voice coil inside the bobbin and making the bobbin thermally conductive, it facilitates heat transfer from the voice coil to the front plate while simultaneously providing mechanical protection and maintaining proper spacing to prevent contact during thermal expansion.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The bobbin structure provides beforehand cushioning by acting as a protective barrier that absorbs and distributes thermal expansion stresses. The bobbin's structural design anticipates thermal expansion and provides a buffer zone that prevents the voice coil from directly contacting the front plate, thereby preventing catastrophic failure before it can occur.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration ensures effective heat dissipation and prevents voice coil rubbing, leading to reduced failure rates and improved performance with higher permanent magnetic field strengths, maintaining accurate and linear sound reproduction while avoiding electrical shorts or opens.

Implementation Method 1

the voice coil is wound solely on the inside surface of a cylindrical bobbin, allowing it to maintain proximity to a thermally conductive front plate

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

high power dissipation loudspeakers... dissipating several kilowatts (kW) for extended periods of time

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS8542865B2Transducer motor structure and inside-only voice coil for use in loudspeakers

Publication Date: 2013.09.24 ONEILL ROBERT M

AI summary

An electromechanical transducer 180, motor structure 200 and voice coil winding support structure or bobbin 210 are configured to protect and transport heat away from a voice coil 220 which is would solely within the interior of bobbin 210 and configured for reciprocating movement in close proximity to an extended cooling pole piece 204. A compact, economical and efficient adaptation of a pancake style motor includes generous volume for a powerful magnet 208, while providing an extended, linear range of excursion and continuous cooling for the generously overhung voice coil 220.