Loudspeaker Passive Low Frequency Directional Control
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Solution Overview
Problem
Existing loudspeaker designs face challenges in achieving directional polar patterns at low frequencies, as they tend to produce omni-directional patterns, and previous solutions either require complex active systems or passive approaches that are not effective in achieving high degrees of attenuation between the front and back.
Innovation Solution
A loudspeaker with a ported enclosure filled with low-density fibrous acoustic material, such as mineral wool, which provides a low-pass characteristic and low-loss properties to delay the back-wave without attenuation, allowing for high front-to-rear attenuation and directional control at low frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive approaches with damping material are used to delay the back-wave, then the complexity and cost are reduced, but the amplitude of the back-wave is attenuated, achieving at best a sub-cardioid response with incomplete cancellation
Solution Approach 1:
The patent uses porous acoustic fill material (such as fiberglass or foam) placed in the rear portion of the enclosure to provide acoustic resistance and delay the back-wave without significant amplitude attenuation. The porous structure creates tortuous flow paths that introduce phase delay while maintaining acoustic energy, enabling effective cardioid cancellation at low frequencies without the need for complex active systems
Solution Approach 2:
The patent changes the acoustic parameters of the enclosure by introducing fill material with specific flow resistance characteristics. By adjusting the density and distribution of the acoustic fill, the system optimizes the phase delay of the back-wave to achieve polarity inversion at the cancellation point behind the loudspeaker, transforming the enclosure's acoustic behavior to enable passive directional control
2Reliability
If secondary transducers are added to cancel acoustic energy in the desired region, then directional polar pattern is achieved, but the number of radiators and amplifiers must be doubled, increasing manufacturing cost
Solution Approach 1:
The patent extracts the directional control function from complex active systems with multiple transducers and simplifies it by using a passive acoustic fill approach within the enclosure. By removing the need for secondary active transducers and their associated amplifiers, the system achieves cardioid polar patterns at low frequencies while significantly reducing component count and manufacturing complexity
Solution Approach 2:
The acoustic fill material serves multiple functions simultaneously: it delays the back-wave through acoustic resistance, provides absorption to control standing waves, and enables passive directional control without requiring external power or active components. The enclosure structure itself becomes the directional control mechanism, eliminating the need for separate active cancellation systems
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 enables a directional polar response with high attenuation between the front and back of the loudspeaker, achieving up to -10 dB at 180 degrees, while minimizing complexity and cost, and can be integrated with single or multiple transducers and high-frequency drivers.
Implementation Method 1
filling at least a portion of the interior chamber of the enclosure with a low density fibrous acoustic fill material placed behind the loudspeaker's transducer so that it extends substantially over and preferably entirely over the enclosure's port openings
Data Source
AI summary
A loudspeaker is provided that passively achieves a directional polar response at low frequencies with a high degree of attenuation between the front and the back of the loudspeaker. The loudspeaker 11 has a transducer 13, an enclosure 21 behind the transducer, and port openings 29 in the sidewalls 23 of the enclosure to allow a back-wave produced by the transducer to exit the enclosure and combine with the front wave produced by the transducer. Cancellation behind the loudspeaker at low frequencies is achieved by delaying the back wave with low loss. Low loss delay at low frequencies is achieved by inserting a low-density fibrous fill material 33 in the acoustic chamber 27 formed behind the transducer 13 by the enclosure 21. A fibrous material is selected having a low-pass transfer function and low acoustic loss in its low-frequency pass band.