Boundary Microphone 35° Angled Holder Directivity
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Solution Overview
Problem
Boundary microphones suffer from insufficient directional characteristics and are prone to comb filter effects due to sound reflections in rooms, leading to peaks and dips in frequency response, which affect sound quality and intelligibility.
Innovation Solution
A small unidirectional microphone element with cardioid-directivity is placed close to a reflective plane at a 35° angle, capturing both direct and reflected sound to synchronize their arrival times, enhancing directivity and reducing noise interference, while a smooth, stiff surface ensures optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a boundary microphone is used to eliminate comb filter effects, then the microphone can be placed at a distance from the speaker, but the directional characteristics become insufficient
Solution Approach 1:
The patent combines a unidirectional microphone element with a boundary layer microphone configuration. The unidirectional element provides directional characteristics while the boundary layer configuration (microphone placed close to a reflective surface) provides the 6dB gain and eliminates comb filter effects. This merging of two microphone types resolves the contradiction between directional characteristics and placement flexibility.
Solution Approach 2:
The patent applies local quality by creating a boundary layer effect in a specific localized area beneath the microphone element. By placing the microphone extremely close to the reflective plane, a boundary layer is formed that selectively enhances sounds from the front while maintaining directional sensitivity. This localized boundary layer configuration improves directional characteristics without sacrificing placement flexibility.
2Measurement precision
If a unidirectional microphone is used to improve directional characteristics, then speech intelligibility improves, but comb filter effects occur due to sound reflections
Solution Approach 1:
The patent converts the harmful reflection effect into a beneficial one by placing the microphone extremely close to the reflective surface. The reflection that would normally cause comb filter effects is now used constructively: the boundary layer formed by the close proximity to the surface causes reflected sounds to arrive at the microphone in phase with direct sounds, producing a 6dB gain and eliminating comb filter effects while maintaining directional characteristics.
3Power
If the microphone is placed close to the reflective plane to eliminate comb filter effects, then a 6dB gain is achieved, but the microphone setup becomes more complex
Solution Approach 1:
The patent merges the unidirectional microphone element with the boundary layer configuration into a single integrated device. This combination achieves the 6dB gain and eliminates comb filter effects while maintaining relatively simple construction. The holder structure provides both the mounting mechanism and the precise positioning relative to the reflective surface, simplifying the overall setup.
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 configuration provides a 6dB gain, allowing for flexible speaker positioning without proximity effect or amplitude variation, improving speech intelligibility and reducing acoustic feedback.
Implementation Method 1
the microphone element picks up the direct sound. Additionally, the benefits of the boundary layer technique, as the microphone element also captures the reflected sound
Implementation Method 2
By using a unidirectional microphone element and placing it in a aligned holder, the directional properties of the element will be improved, as the microphone element picks up the direct sound. Additionally, the benefits of the boundary layer technique, as the microphone element also captures the reflected sound, can be gained
Data Source
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Figure 3~4
AI summary
A high directivity boundary microphone (10) is disclosed, build up of a normal unidirectional microphone element (12) with cardioid-directivity behavior. The microphone element (12) is placed on a holder plate (14), with a membrane(16) of the microphone element (12) facing a plane (18) where a holder (20), comprising the holder plate (14) and a holder feet (22), is placed upon. The holder (20) ensures that the microphone element (12) is aligned at an angle (24) of preferably 35° respective to the plane (18). In this position, the microphone element (12) can detect direct sound (26) in a defined speech area (28A, 28B) as well as delayed sound (30) that is reflected at the plane (18) beneath the microphone element (12). Outside the defined speech area (28A, 28B) the sensitivity is strongly reduced.