Sound Sponge Block for Loudspeaker Size Reduction
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Solution Overview
Problem
Current loudspeaker technologies for mobile products face challenges with light flexible diaphragms that cannot work with sealed-cavity designs due to stiffness issues, leading to reduced low-frequency output, and open back designs result in sound cancellation, necessitating the use of inefficient moving coil speakers, while traditional sound absorbing materials are ineffective at lower frequencies, limiting cabinet size reduction.
Innovation Solution
A sound sponge block with multiple parallel ducts of predetermined geometrical dimensions is placed behind the diaphragm to absorb sound waves radiated in the backward direction, reducing impedance and allowing for a smaller loudspeaker size without physically touching the diaphragm, using ducts that are typically round cylinders with diameters between 0.1 and 10 microns and sealed ends with infinite specific termination impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If sealed-cavity design is used with light flexible diaphragms, then cabinet size can be reduced, but low frequency output is greatly reduced due to excessive stiffness
Solution Approach 1:
The patent uses a sound sponge block with porous structure containing multiple ducts of specific dimensions (0.1-10 microns) placed behind the diaphragm. This porous structure absorbs sound waves at low frequencies without creating the stiffness problem of sealed cavities, enabling small cabinet size while maintaining bass response.
Solution Approach 2:
The patent changes the acoustic impedance parameters by using ducts with specific geometrical dimensions (diameter 0.1-10 microns, length 10-1000 microns) and specific termination impedance (infinite at sealed ends). These parameter changes allow the sound sponge to effectively absorb low frequency waves while keeping the cabinet compact.
2Volume of stationary object
If open back design is used with light flexible diaphragms, then cabinet size can be reduced, but sound cancellation occurs because rear and front waves are in opposite phase
Solution Approach 1:
The patent converts the harmful rear-radiated sound waves that would cause cancellation into a beneficial effect by using the sound sponge block to absorb these waves. The absorption transforms the problematic backward radiation into useful acoustic energy dissipation, preventing cancellation while maintaining compact dimensions.
3Reliability
If traditional sound absorbing materials are used, then standing waves can be controlled, but they have little effect at lower frequencies and cabinet size cannot be reduced significantly
Solution Approach 1:
The patent fundamentally changes the parameters of sound absorbing materials by using ducts with dimensions in the micron range (0.1-10 microns diameter, 10-1000 microns length) rather than traditional macroscopic porous materials. This parameter change enables effective low frequency absorption in a compact volume, overcoming the limitation of conventional materials.
Solution Approach 2:
The patent transitions from traditional macroscopic sound absorbing materials to microscopic duct structures, effectively moving the absorption mechanism to another dimension (micron scale). This dimensional change allows the sound sponge block to achieve low frequency absorption in a much smaller volume than traditional materials permit.
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 solution enables the use of high-efficiency, high-quality membrane-type loudspeakers in small spaces by effectively absorbing lower frequency waves, overcoming the limitations of traditional materials and allowing for reduced cabinet size without bass loss, and enabling the integration of loudspeakers with displays in mobile devices.
Implementation Method 1
a sound sponge block comprising multiple ducts made of a pre-selected material placed behind the diaphragm without physically touching the diaphragm, wherein the multiple ducts have predetermined geometrical dimensions to substantially absorb the sound waves radiated from a rear side of the diaphragm in the backward direction
Data Source
AI summary
The specification and drawings present a new method and apparatus for reducing loudspeaker size by partitioning the back cavity of the loudspeaker using a sound sponge block. The sound sponge block is an array of narrow ducts (e.g., parallel ducts, or parallel round cylinders of a small diameter) made of a pre-selected material with predetermined dimensions (e.g., the diameter and length) formed within a single block which is placed behind a loudspeaker diaphragm but not in a direct contact with it. The sound sponge block, comprising the multiple very narrow ducts (e.g., with duct diameters on the order of microns) substantially absorbs the sound waves radiated from a rear side of the diaphragm in the backward direction due to significant drop in the impedance for very narrow tube diameters.