Helmholtz Resonator Sound Absorber for Low-Frequency Engine Noise
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Solution Overview
Problem
Existing sound absorbents in vehicle engine compartments are inefficient at damping low-frequency sound due to space constraints, as increasing their thickness to improve damping is limited by available space.
Innovation Solution
A sound absorbent device comprising a base layer with compartments configured as Helmholtz resonators and a cover layer, combined with a sound transmission loss panel, which together efficiently dampen a broader range of frequencies, including low frequencies, within a compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the thickness of sound absorbent material is increased to dampen low frequency sound, then low frequency sound damping is improved, but the device occupies more space which is limited in the engine compartment
Solution Approach 1:
The patent changes the physical parameters of the sound absorbent material by incorporating Helmholtz resonators with specific cavity volumes and neck dimensions. These resonators are tuned to resonate at low frequencies, allowing effective low-frequency sound damping without requiring increased material thickness. The resonator geometry parameters (cavity volume, neck area, neck length) are optimized to achieve targeted frequency response.
Solution Approach 2:
The patent employs a composite structure combining traditional porous sound absorbent material with Helmholtz resonator cavities. This composite design integrates two different sound damping mechanisms: porous absorption for mid-to-high frequencies and resonator-based absorption for low frequencies, achieving broad-spectrum noise control within a compact thickness.
2Object-affected harmful factors
If traditional sound absorbent materials are used to dampen noise, then higher frequency sound is dampened effectively, but low frequency sound damping is insufficient
Solution Approach 1:
The patent segments the sound damping function across different frequency ranges by incorporating multiple Helmholtz resonators with different tuning frequencies into the base layer. Each resonator targets specific low-frequency bands, while the porous material handles higher frequencies, creating a segmented approach to broad-spectrum noise control.
Solution Approach 2:
The patent modifies the acoustic parameters of the sound damping system by introducing resonators with specific resonance frequencies. The resonator frequency is determined by parameters such as cavity volume, neck cross-sectional area, and neck length, allowing tuning to target specific low-frequency noise sources while maintaining effectiveness across a broad frequency spectrum.
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 device effectively dampens a wide frequency range of noise, including low frequencies, while maintaining a thin profile, enhancing noise reduction in vehicle engine compartments.
Implementation Method 1
each opening through the cover layer is configured such that a respective Helmholz resonator is formed in each compartment
Implementation Method 2
The sound transmission loss panel provides damping of higher frequency sound than sound for which the resonators of the base layer are tuned
Implementation Method 3
the base layer and the cover layer work together according to the Helmholz principle and may not be able to efficiently prevent sound of certain frequencies from being transmitted through the base layer and the cover layer
Data Source
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AI summary
The present disclosure relates to a sound absorbent device (1) comprising a base layer (2) and a cover layer (3). The base layer (2) comprises at least one compartment (4). The cover layer (3) is attached to base layer (2) such that a respective cavity is formed in each compartment (4). The cover layer (3) comprises, for each compartment (4), a respective opening through the cover layer (3) to each respective cavity. Also, each opening through the cover layer (3) is configured such that a respective Helmholz resonator is formed in each compartment (4). The present disclosure also relates to an assembly comprising a plurality of such sound absorbent devices (1) connected side-by-side.