Acoustically Open Headphones Active Noise Reduction

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Solution Overview

Problem

Open headphones fail to maintain effective audio listening experience in noisy environments above 70dBA due to diminished situational awareness and noise interference, as they allow external sounds to reach the user but struggle to filter out ambient noise effectively.

Innovation Solution

The design incorporates an electroacoustic transducer with a support structure and multiple microphones, including a feed-forward microphone and a feedback microphone, coupled to a processor that operates the transducer to actively reduce targeted sound pressure waves, maintaining acoustic openness while minimizing noise interference, and adjusts noise reduction based on environmental noise levels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If open headphones are designed to sit off the ears to allow outside sounds to reach the wearer's ears, then situational awareness and natural voice perception are improved, but noise interference from external environments above 70dBA deteriorates the audio listening experience

Engineering Contradiction:

Improvesituational awarenessVSAvoidnoise interference

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

A feedback microphone is positioned between the transducer and the user's ear to capture sound pressure waves. The processor uses this feedback signal to generate anti-noise that is played through the transducer, actively reducing ambient noise while preserving the open headphone design that allows situational awareness

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

An electroacoustic transducer serves as an intermediary device that generates anti-noise sound waves to cancel ambient noise. The transducer is positioned to interfere destructively with incoming sound waves, reducing noise interference without requiring the headphones to occlude the ear

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If traditional closed headphones are used to block external noise, then noise interference is reduced, but situational awareness and natural voice perception are lost

Engineering Contradiction:

Improvenoise interferenceVSAvoidsituational awareness

Core Design Contradiction:

Object-affected harmful factorsVSEase of operation

Solution Approach 1:

The mechanical passive noise blocking system is replaced with an active electronic noise reduction system. Instead of physically blocking sound waves with closed ear cups, the system uses microphones to detect noise and electroacoustic transducers to generate anti-noise, achieving noise reduction while maintaining acoustic openness for situational awareness

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Object-affected harmful factors

If the transducer is operated to actively reduce targeted sound pressure waves, then noise interference is reduced, but the acoustic openness of the headphone may be compromised

Engineering Contradiction:

Improvenoise interferenceVSAvoidacoustic openness

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The noise reduction effect is localized to specific frequency ranges and directions. The feedback microphone and transducer are positioned to create noise cancellation primarily in the direction of ambient noise sources, while maintaining acoustic openness for natural voice perception and situational awareness in other directions

Inventive Principle:

Principle #3Local quality

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 solution enhances the audio listening experience by actively reducing noise in noisy environments, maintaining situational awareness and natural voice perception, effectively increasing the usability of open headphones in environments above 70dBA by providing equivalent volume amplification of the audio program.

Implementation Method 1

an electroacoustic transducer and a support structure for suspending the transducer adjacent to a user's ear

Methodology Applied

Scientific EffectElectroacoustic transduction:

Implementation Method 2

The first microphone is coupled to one or more of the transducer and the support structure such that the first microphone is located in a substantially broadband acoustic null of the transducer. The microphone receives sound pressure waves and outputs a related electronic signal to the processor

Methodology Applied

Scientific EffectAcoustic detection:

Implementation Method 3

The processor uses the electronic signal to operate the transducer to reduce targeted sound pressure waves at the user's ear

Methodology Applied

Scientific EffectAcoustic interference: Interference

Data Source

PatentEP3491837B1Acoustically open headphone with active noise reduction

Publication Date: 2023.05.10 BOSE CORP

Figure 1
Figure 2A~2B
Figure 3~4

AI summary

A headphone includes an electroacoustic transducer and a support structure for suspending the transducer adjacent to a user's ear when worn by the user such that the headphone is acoustically open. A first microphone is coupled to one or more of the transducer and the support structure such that the first microphone is located in a substantially broadband acoustic null of the transducer. A processor is coupled to the headphone. The microphone receives sound pressure waves and outputs a related electronic signal to the processor. The processor uses the electronic signal to operate the transducer to reduce targeted sound pressure waves at the user's ear.