Monobloc Mandrel for Voice-Coil Motor Mode Coupling
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Solution Overview
Problem
The existing voice-coil transducer motor assemblies in loudspeakers suffer from nonlinearities due to mode coupling between mechanical and acoustical modes, leading to reduced clarity and audibility of sound, especially at high frequencies, caused by the reduced rigidity and increased weight of the mandrel and diaphragm.
Innovation Solution
A monobloc mandrel with a natural mechanical mode of vibration outside the audible frequency range is designed, using a closed pore material that is both rigid and light, with integrated coil windings and a ferrofluid seal system to prevent mode coupling, and is manufactured through injection casting or machining to ensure structural integrity and electrical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the mandrel is made lighter to reduce inertia, then the yield is improved, but the rigidity is reduced causing mode coupling and nonlinearities
Solution Approach 1:
The mandrel is made from a composite material consisting of a porous core material (such as foam or sponge) and a reinforcing material (such as fiber glass, carbon fiber, or metal mesh). This composite structure provides both reduced weight and maintained rigidity, resolving the contradiction between lightweight design and structural strength.
Solution Approach 2:
The mandrel features a non-uniform wall thickness distribution, with thicker sections at the ends and thinner sections in the middle. This local variation in material distribution optimizes the rigidity-to-weight ratio, providing enhanced structural strength where needed while minimizing overall weight.
2Strength
If the mandrel rigidity is increased to prevent mode coupling, then the frequency response is improved, but the weight increases reducing yield
Solution Approach 1:
The composite construction with porous core and reinforcing shell provides high rigidity relative to weight, allowing the mandrel to resist mode coupling while maintaining low overall mass for improved yield.
Solution Approach 2:
The non-uniform wall thickness concentrates material where structural support is most needed (at the ends), providing maximum rigidity with minimum material usage, thus optimizing the rigidity-to-weight ratio.
3Weight of moving object
If the mandrel and diaphragm are made as light as possible, then the inertia is reduced, but mode coupling occurs between mechanical and acoustical modes
Solution Approach 1:
The composite mandrel structure provides sufficient rigidity to prevent mode coupling between mechanical and acoustical modes while maintaining low weight, ensuring linear frequency response and reliable audio reproduction.
Solution Approach 2:
The strategically thicker end sections of the mandrel provide structural reinforcement that prevents mode coupling, while the thinner middle sections minimize weight, achieving both low inertia and reliable frequency response.
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
The solution effectively reduces mode coupling, resulting in clearer and more accurate sound production by isolating mechanical and acoustical modes beyond the audible frequency range, enhancing the frequency response and reducing energy absorption, thereby improving the overall sound quality.
Implementation Method 1
said monobloc structure of the mandrel may comprise a closed pore material, that results in having a rigid as well as a light moving part
Implementation Method 2
comprise magnetic field generating means adapted to generate a magnetic field in which a coil fixed on a moving part also called mandrel or voice coil support, can be driven by a driving current in order to induce vibrations
Implementation Method 3
the outer surface of the mandrel may be coated with a material that is resistant to being wetted through contact with a ferrofluid seal
Data Source
Figure 1~2
Figure 3~4
Figure 5A~5B
AI summary
The invention relates to a mandrel (21) for a coil transducer motor structure (10) adapted to receive at least one coil (22H, 22L) wound therearound arranged in use for displacing the mandrel (21) along an axis of displacement Z, as a current is driven through the coils (22H, 22L) when the mandrel (21) is placed in a magnetic field, characterized in that the mandrel (21) has a monobloc structure with a natural mechanical mode of vibration outside of the audible frequency range.