Linearly Compressed Microphone Interference Tube for Low-Frequency Attenuation
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Solution Overview
Problem
Existing shotgun microphones face limitations in effectively attenuating off-axis sound frequencies due to the length of their interference tubes, and certain applications impose constraints on the permissible linear footprint, making it impractical to achieve desired frequency cancellation.
Innovation Solution
The interference tube features a non-linear internal acoustic path with sound entrance holes, allowing sound waves to enter at varying lengths, resulting in destructive interference and extended low-frequency attenuation without increasing the external dimension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the interference tube length is increased to attenuate lower frequency off-axis sounds, then the frequency attenuation performance is improved, but the linear footprint of the microphone increases
Solution Approach 1:
The interference tube employs a non-linear, three-dimensional internal acoustic path that folds back on itself, transforming the linear dimension into a multi-dimensional configuration. This allows the acoustic path length to exceed the external linear footprint, enabling lower frequency attenuation without increasing the overall microphone length. The tube bends and curves internally while maintaining a compact external form factor.
Solution Approach 2:
The interference tube's internal acoustic path is nested within its own external structure, with the acoustic pathway folding back and nesting within the tube's body. This nesting allows the acoustic path to achieve greater effective length by utilizing the internal volume of the tube itself, rather than requiring additional external space.
2Reliability
If the interference tube length is increased to achieve desired frequency cancellation, then the acoustic performance is improved, but the device becomes impractical for applications with footprint constraints
Solution Approach 1:
By transitioning from a linear one-dimensional tube to a non-linear three-dimensional acoustic path, the design achieves extended low-frequency attenuation capability while maintaining a compact footprint suitable for various applications. The dimensional transformation allows the tube to adapt to space-constrained environments without sacrificing acoustic performance.
3Ease of manufacture
If a straight interference tube is used, then the structure is simple and manufacturing is easier, but the internal acoustic path length is limited by the external dimension
Solution Approach 1:
The interference tube employs curved and bent geometries instead of straight lines, creating a non-linear acoustic path that folds back on itself. This curvature allows the internal acoustic path to achieve greater length while maintaining manufacturability through standard tubing bending processes. The curved design is more complex than a straight tube but remains practical to manufacture.
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 non-linear geometry enables effective reduction of off-axis sound waves at lower frequencies, maintaining the same linear footprint as conventional tubes, thus enhancing the microphone's directional performance.
Implementation Method 1
Off-axis sounds may enter the tube at various lengths from the capsule and may consequently arrive at the capsule out of phase with one another and experience phase interference or phase cancellation (also known as deconstructive interference).
Data Source
AI summary
Apparatuses and methods for a linearly compressed interference tube for use with microphones having an internal acoustic path with a geometry that approximates a longer interference tube within the same linear footprint in order to provide improved low-frequency attenuation and stable polar patterns in the microphones.