Double Chamber Loudspeaker Enclosure for Low-Frequency Extension
Solution Overview
Problem
Loudspeaker systems face challenges when mounted in small, complex cavities, such as those in vehicles, due to increased air stiffness, turbulent noise, pressure imbalances, and asymmetrical mode-shapes, which limit low-frequency extension and increase costs due to the need for stiff and heavy enclosures.
Innovation Solution
A loudspeaker system with two separate air volumes acoustically linked by a port, where the air mass in the port does not contribute to acoustic radiation, forming a resonant system driven by the transducer, and using an Adapter for Passive Diaphragm Control (APDC) to decouple the untuned volume from the diaphragm, providing a deterministic rear load and reducing rocking modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If a loudspeaker driver unit is mounted into a small sealed enclosure, then the enclosure size is reduced, but the air stiffness increases which raises the coupled resonance and curtails low frequency extension
Solution Approach 1:
The enclosure is divided into two separate air volumes (first and second volumes) that are acoustically linked by a port. This segmentation allows each volume to be optimized independently - the first volume directly coupled to the diaphragm can be small while the second volume provides additional acoustic compliance, effectively reducing the overall air stiffness effect on the driver.
Solution Approach 2:
A port enclosing a plug of air is introduced as an intermediary acoustic element between the two air volumes. This port allows acoustic energy to transfer between volumes while the plug of air provides acoustic compliance, mediating the interaction between the driver and the enclosure volumes to reduce the harmful stiffness effect.
2Volume of stationary object
If the loudspeaker is mounted in a small enclosure, then the enclosure size is reduced, but the driver must be mechanically very stiff and heavy to minimize air stiffness influence, increasing cost
Solution Approach 1:
By segmenting the enclosure into two volumes, the system achieves the desired acoustic compliance without requiring the driver itself to be mechanically stiff and heavy. The acoustic compliance is provided by the enclosed air volumes and port configuration rather than by expensive stiff driver construction.
3Adaptability or versatility
If the loudspeaker is mounted in a vehicle body cavity, then installation flexibility is improved, but non-uniform pressure distribution causes asymmetrical mode-shapes and rocking modes, reducing reliability
Solution Approach 1:
The port enclosing a plug of air acts as an intermediary that decouples the driver from the non-uniform pressure environment of the vehicle cavity. The first air volume directly coupled to the diaphragm provides a more uniform acoustic environment, while the port mediates the connection to the second volume, reducing the impact of asymmetrical pressure distributions and rocking modes.
Solution Approach 2:
Segmenting the acoustic system into two volumes with a port allows the driver to operate in a more controlled acoustic environment (first volume) while the second volume handles the interaction with the variable vehicle cavity, improving performance stability across different installation conditions.
4Object-affected harmful factors
If a port is used to link air volumes, then low frequency extension is improved, but the air mass in the port may form part of acoustic radiation, causing unwanted effects
Solution Approach 1:
The port is designed with an enclosed plug of air nested within the enclosure structure. This configuration allows the port to provide the beneficial acoustic coupling between volumes for low frequency extension while the enclosed nature of the plug prevents the port air mass from forming part of the external acoustic radiation.
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 enhances low-frequency extension, reduces rocking modes, and allows for predictable performance in small enclosures without additional damping, enabling efficient bass reproduction and heat dissipation while using lower-cost drive units.
Implementation Method 1
The air volume which is directly coupled to the diaphragm and the plug of air in the port are tuned to form a resonant system driven by the transducer
Implementation Method 2
an electro-acoustical transducer that converts electrical power into acoustical power
Implementation Method 3
the front side of the diaphragm radiates sound into a listening environment
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A loudspeaker system is presented which comprises an enclosure (4,6) with two separate air volumes (3,5) which are acoustically linked by a port (7); the port enclosing a plug of air; and an electro-acoustical transducer (1) that converts electrical power into acoustical power and that comprises a diaphragm (2) having a front side and a rear side; the front side of the diaphragm radiates sound into a listening environment and the rear side is directly acoustically coupled to one (5) of the volumes of the enclosure (4,6). The air volume (5) which is directly coupled to the diaphragm (2) and the plug of air located in the port are tuned to form a resonant system driven by the transducer; and the volume (3) that is not directly coupled to the diaphragm (2), is coupled to the plug of air in the port (7).