Moisture-Resistant Earmuff Sound Absorber with Integral Skin

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Solution Overview

Problem

Conventional open cell earmuff sound absorbers absorb not only sound but also water and moisture, leading to condensation and potential microbial growth in humid environments, requiring frequent drying and replacement.

Innovation Solution

A moisture-resistant integral skin is applied to the sound absorber, surrounding an open cell foam interior with lower density and greater porosity, to prevent moisture absorption and soiling, while maintaining effective sound attenuation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional open cell foam is used as sound absorber, then sound absorption performance is improved, but moisture absorption and condensation occur leading to microbial growth

Engineering Contradiction:

Improvesound absorption performanceVSAvoidmoisture absorption and microbial growth

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The sound absorber is segmented into two distinct parts: an outer skin layer and an inner open cell foam core. The outer skin acts as a moisture barrier while the inner foam provides sound absorption, resolving the contradiction between sound absorption performance and moisture resistance by dividing the functional requirements into separate structural components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The sound absorber uses a composite structure combining a non-porous or low-porosity outer skin material with an open cell foam inner core. This composite material approach allows the device to simultaneously achieve moisture resistance from the outer skin and effective sound absorption from the porous inner foam, eliminating the need to choose between these conflicting properties.

Inventive Principle:

Principle #40Composite materials

2Reliability

If open cell foam is used for sound absorption, then noise blocking capability is improved, but the sound absorber requires frequent drying and replacement

Engineering Contradiction:

Improvenoise blocking capabilityVSAvoidservice life before drying/replacement

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The outer skin is applied in advance to the sound absorber core during manufacturing, creating a pre-assembled moisture barrier before the product reaches the user. This preliminary protective action prevents moisture ingress from the start, eliminating the need for frequent user-side drying and replacement operations throughout the product's service life.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention converts the inherently porous nature of foam (which normally causes moisture problems) into a benefit by using it only for its sound absorption function in the protected inner core, while the outer skin handles all moisture exposure. This allows the foam's porosity to be fully utilized for acoustic performance without suffering from its moisture absorption drawback.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Object-affected harmful factors

If outer skin is added to prevent moisture, then moisture resistance is improved, but device complexity increases

Engineering Contradiction:

Improvemoisture resistanceVSAvoidsound absorber structure

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The outer skin is implemented as a thin film or shell layer that conforms to the shape of the foam core, providing moisture protection with minimal added complexity. This thin-film approach adds the necessary protective function without significantly increasing the overall device complexity, weight, or manufacturing difficulty compared to solid barrier materials.

Inventive Principle:

Principle #30Flexible shells and thin films

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 effectively reduces moisture absorption and condensation within the earmuff, preventing microbial growth and maintaining sound attenuation performance, even in cold humid conditions, with a moisture content reduction of approximately 62% compared to traditional open cell foam absorbers.

Implementation Method 1

a sound absorber having a moisture-resistant integral skin substantially surrounding an open cell foam interior

Methodology Applied

Scientific EffectHydrophobic barrier: Hydrophobe

Implementation Method 2

the sound absorber usually is made from open cell foam

Methodology Applied

Scientific EffectAcoustic absorption: Acoustic Absorption

Data Source

PatentEP2547300B1Hearing protective device with moisture resistant earmuff sound absorbers

Publication Date: 2020.06.03 3M INNOVATIVE PROPERTIES CO

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AI summary

An earmuff hearing protective device whose earmuffs each include a generally cup-shaped, substantially rigid shell having a head-facing rim; a head-engaging, ear-encircling cushion affixed to the rim; and a sound absorber inside the shell. The sound absorber has a moisture-resistant integral skin substantially surrounding an open cell foam interior having lower density and greater porosity than that of the skin. The skin helps discourage moisture pickup and microbial growth.