Speaker Chassis Spoke Design for Magnetic Leakage Control
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Solution Overview
Problem
Speaker apparatuses with large diameters, such as woofers and sub-woofers, face a decrease in speaker output due to magnetic field leakage, as the magnetic flux density in the magnetic gap decreases when the magnetic field generating unit is fixed to a speaker frame made of iron, leading to reduced rigidity and increased oscillation.
Innovation Solution
The speaker apparatus employs a counter-drive method where the magnetic field generating unit is fixed to the center of a recess in a support chassis made of magnetic metal, with spoke parts having a narrower inner end and wider outer end, increasing magnetic flux transmission resistance and reducing leakage, and additional ribs are formed around holes in the spoke parts to enhance structural strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the magnetic field generating unit is fixed to the center on the recess side of the iron speaker frame, then the speaker apparatus can be made thin, but the leaked magnetic flux is easily attracted into the frame arm, causing speaker output to decrease
Solution Approach 1:
The frame arm is designed with non-uniform thickness, being thinner at the inner end near the magnetic field generating unit and thicker at the outer end. This local variation in quality allows the frame arm to provide structural support while reducing magnetic flux attraction at the critical location near the magnet.
Solution Approach 2:
A magnetic flux barrier is introduced as an intermediary component between the magnetic field generating unit and the frame arm. This barrier, made of materials with low magnetic permeability such as resin or plastic, mediates the interaction by blocking the path of leaked magnetic flux, preventing it from being attracted into the frame arm while allowing the frame arm to maintain its structural function.
2Ease of manufacture
If the frame arm has even width dimension, then the manufacturing is simple, but the leaked magnetic field is easily attracted into the frame arm
Solution Approach 1:
The frame arm transitions from uniform width to non-uniform width, with the inner end being thinner and the outer end being thicker. This local quality change reduces magnetic permeability at the inner end where magnetic flux leakage occurs, while maintaining sufficient structural strength at the outer end.
Solution Approach 2:
The design accepts that the frame arm will attract some magnetic flux, but converts this potential harm into a benefit by strategically placing the magnetic flux barrier. The barrier redirects the leaked magnetic flux through a controlled path, preventing it from significantly reducing the magnetic flux density in the magnetic gap.
3Strength
If the speaker frame is made thick to increase rigidity, then the oscillation transmission is reduced, but the magnetic flux density in the magnetic gap decreases due to magnetic field attraction
Solution Approach 1:
Instead of uniformly increasing the frame arm thickness, the design applies local quality variation by making the inner end thinner and the outer end thicker. This provides sufficient rigidity at the outer end for structural support while reducing magnetic flux attraction at the inner end near the magnetic field generating unit.
Solution Approach 2:
The magnetic flux barrier serves as an intermediary that decouples the relationship between frame thickness and magnetic flux attraction. It allows the frame arm to maintain adequate thickness for rigidity without proportionally increasing magnetic flux attraction, as the barrier blocks the flux path before it can be significantly attracted into the frame.
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 effectively reduces the attraction of leaked magnetic flux into the support chassis, maintaining speaker output by increasing magnetic flux density in the magnetic gap and ensuring sufficient structural strength to support the magnetic field generating unit.
Implementation Method 1
a magnetic field generating unit configured to apply a driving magnetic field to the voice coil
Implementation Method 2
the support chassis includes a frame part formed of a magnetic metal material and fixed to the main-body chassis
Data Source
AI summary
A support chassis mounted on a sounding side of a speaker apparatus is formed of an iron material. The support chassis is formed in a shape in which a central supporting part nears a main-body chassis. A magnetic field generating unit is fixed to the central supporting part on a side of a recess of the support chassis. The support chassis includes a frame part, the central supporting part, and spoke parts. In the spoke part, a width dimension D1 of an inner end part is formed narrower than a width dimension D2 of an outer end part. Therefore, a resistance in a case where a magnetic flux passes through the spoke part increases, and the leaked magnetic field is hardly induced from the magnetic field generating unit to the spoke part. Therefore, a reduction in a speaker output can be prevented.