Compression Driver Voice Coil Former Holes
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Solution Overview
Problem
Conventional compression drivers experience irregular modal excitation and resonance issues due to irregular acoustic impedance and additional sound radiation through magnetic gaps, making it difficult to balance and minimize these effects.
Innovation Solution
A compression driver design with a diaphragm and phase plug configuration that includes holes in the voice coil former to extend the compression cavity, bypassing the magnetic gap with lower impedance, and incorporating mechanical compliance through arcuate spars to minimize cavity modes and improve sound transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the compression cavity is sealed to contain sound, then sound pressure is improved, but modal excitation and resonance become irregular and difficult to control
Solution Approach 1:
The compression cavity is divided into two separate cavities: a sealed compression cavity for containing sound pressure, and an unsealed extension cavity that opens into the surround cavity. This segmentation allows each cavity to serve its specific function - the sealed one maintains pressure while the unsealed one provides acoustic loading and resonance control.
Solution Approach 2:
The extension cavity acts as an intermediary between the sealed compression cavity and the surround cavity. It provides a controlled acoustic pathway that allows sound to be loaded by the surround cavity's resonance, thereby balancing modal excitation while maintaining the pressure benefits of the sealed compression cavity.
2Power
If the magnetic gap is used for sound radiation, then acoustic energy is improved, but acoustic impedance becomes irregular and Helmholtz resonances occur
Solution Approach 1:
The harmful Helmholtz resonances from the magnetic gap are extracted and transferred to the extension cavity. By providing a separate controlled pathway through the extension cavity, the irregular acoustic impedance effects are isolated from the main compression cavity, allowing the magnetic gap to function purely for sound radiation.
3Temperature
If ferrofluid is used in the magnetic gap, then heat dissipation is improved, but sound radiation through the gap is prevented
Solution Approach 1:
The acoustic pathways are segmented into two separate routes: sound radiates through the magnetic gap for direct acoustic energy, while a separate pathway through the extension cavity provides acoustic loading. This allows ferrofluid to be present in the magnetic gap for heat dissipation without blocking all sound radiation, as the extension cavity provides an alternative acoustic pathway.
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 design significantly reduces acoustic excitation in the gap and enhances sound transmission efficiency, allowing for improved frequency response and increased high-frequency acoustic energy emission.
Implementation Method 1
bypassing the magnetic gap with lower impedance
Implementation Method 2
enhances sound transmission efficiency
Implementation Method 3
incorporating mechanical compliance through arcuate spars to minimize cavity modes
Implementation Method 4
minimize cavity modes
Implementation Method 5
the diaphragm to vibrate and so radiate acoustic waves
Implementation Method 6
Passing an audio signal current through the voice coil induces a force, causing the voice coil driver to reciprocate between the poles of the magnet
Implementation Method 7
The phase plug usually has channels passing through it to collect the sound radiated by the diaphragm and to channel it towards the horn
Implementation Method 8
each channel will excite radial modes in the compression cavity depending on their diameter and area
Implementation Method 9
using ferrofluid in the magnetic gap between the magnets and the voice coil former forms a seal preventing sound passing into the magnetic gap
Data Source
Figure 1
Figure 2a~2b
Figure 2c~2d
AI summary
A compression driver comprising a diaphragm having a concave sound-radiating surface, a phase plug having a convex surface shaped to match the concave surface of the diaphragm, and a magnet, the diaphragm being connected to a voice coil former along a line forming a closed loop, the diaphragm and former being adapted to reciprocate along an axis, the diaphragm, phase plug, voice coil former together being configured to form: a compression cavity; a surround cavity; and a magnet cavity, in which an abstract surface can be generated by rotating about the axis an abstract line extending from the diaphragm on the line of the closed loop to the convex surface of the phase plug perpendicularly thereto, and in which a plurality of holes are formed in the voice coil former around at least a part of its circumference and pass through the voice coil former to connect the compression cavity with the surround cavity, the holes having a total area substantially the same as the area of the abstract surface.