Hemi-anechoic Acoustic Source Waveguide Positioning
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Solution Overview
Problem
Existing acoustic sources in hemi-anechoic chambers fail to meet the directionality requirements of ISO 3745:2003(E) up to 20 kHz unless mounted in the reflecting plane, limiting their low-frequency performance and directivity.
Innovation Solution
An acoustic source assembly comprising a compression driver, throat adapter, and waveguide is positioned outside the measurement hemisphere, with the waveguide end close to the reflecting plane to create a near-point source effect, meeting the ISO standard by channeling sound into the measurement hemisphere while minimizing breakout noise through damping materials and adjustable positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the acoustic source is mounted in the reflecting plane to meet directionality requirements, then directivity is improved, but low-frequency performance deteriorates
Solution Approach 1:
The patent transitions from mounting the source directly in the reflecting plane (2D position) to suspending it above the plane using a rigid rod (adding vertical dimension Z). This dimensional change allows the source to meet directivity requirements through geometric positioning while avoiding the low-frequency performance degradation associated with in-plane mounting.
Solution Approach 2:
A rigid rod is introduced as an intermediary element between the acoustic source and the reflecting plane. This mediator enables precise positioning above the plane while mechanically supporting the source, resolving the contradiction between achieving proper directivity and maintaining low-frequency performance.
2Manufacturing precision
If the compression driver throat is reduced to a smaller diameter, then directivity is improved, but acoustic energy transmission deteriorates
Solution Approach 1:
The patent implements a nested structure where a smaller diameter compression driver throat is positioned inside a larger diameter horn. The throat adapter connects these two elements, allowing the small throat to provide directional control while the larger horn maintains acoustic energy transmission, thus resolving the contradiction between directivity and power.
Solution Approach 2:
The solution adds a spatial dimension by introducing the horn structure that surrounds and extends from the compression driver throat. This dimensional expansion allows the system to maintain small throat diameter for directivity while the larger horn volume preserves acoustic energy transmission capability.
3Object-generated harmful factors
If damping material is added to reduce breakout noise, then noise control is improved, but device complexity increases
Solution Approach 1:
The patent uses a thin flexible membrane made of damping material that conforms to the horn's internal geometry. This thin-film approach effectively reduces breakout noise while adding minimal structural complexity, as the membrane integrates smoothly with the existing horn structure rather than requiring separate bulky damping components.
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 ensures compliance with ISO 3745:2003(E) by maintaining directivity and low-frequency performance above the reflecting plane, allowing for precise sound testing in hemi-anechoic chambers without disturbing the acoustic field inside the measurement hemisphere.
Implementation Method 1
A waveguide assembly couples to the exit aperture of the throat adapter and channels the sound to the opposite end of the waveguide from which sound emanates
Implementation Method 2
A tubing of damping material surrounds the waveguide to reduce the possibility of breakout noise
Implementation Method 3
One end of a waveguide assembly couples to the exit aperture of the throat adapter and channels the sound to the opposite end of the waveguide from which sound emanates
Data Source
AI summary
Embodiments include an acoustic source for use in a hemi-anechoic chamber comprising a source assembly and a waveguide assembly for producing sound outside of a measurement hemisphere and channeling the sound into the measurement hemisphere. A waveguide end from which sound emanates is positioned close to the reflecting plane of the chamber and can approximate a point source.