ANR Headset Gain Control via Transducer Displacement
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Solution Overview
Problem
Conventional active noise reduction (ANR) headsets reduce loop gain based on drive signal voltage, leading to over-constraint of the electroacoustic transducer and reduced sound pressure levels, especially when the ear cup is not completely sealed against the user's head, resulting in insufficient noise cancellation.
Innovation Solution
A gain adjustment circuit that modifies the ANR loop gain based on the displacement of the electroacoustic transducer components, using a displacement-sensing compressor to adapt to varying seal conditions between the headset and the user's head, allowing for increased sound pressure levels and preventing transducer damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the ear cup is not completely sealed against the user's head, then the air spring constant decreases allowing greater transducer displacement, but the transducer can be over-extended even with normal voltage drive signal levels
Solution Approach 1:
The compressor threshold is made dynamic by making it a function of frequency rather than a fixed value. The threshold detector compares the instantaneous frequency of the drive signal to a predetermined frequency threshold, and only activates compression when both the voltage exceeds the frequency-dependent threshold AND the frequency exceeds the threshold. This allows the system to adapt its protection level based on operating conditions while maintaining reliability.
Solution Approach 2:
The invention changes the parameter used for compression activation from a simple fixed voltage threshold to a frequency-dependent voltage threshold. By incorporating frequency detection and comparison, the system adjusts the effective threshold based on the operating frequency, allowing optimal protection across different seal conditions and frequency ranges without over-constraining the transducer in normal operating conditions.
2Reliability
If the compressor reduces ANR loop gain based on drive signal voltage threshold, then the transducer is protected from over-extension, but the sound pressure levels are reduced especially when ear cup seal is poor
Solution Approach 1:
The compression activation is made dynamic through frequency-dependent thresholding. The system continuously monitors the frequency of the drive signal and adjusts the compression activation accordingly. This dynamic approach allows the system to maintain high output power in normal conditions while providing protection when needed, resolving the contradiction between power output and protection.
Solution Approach 2:
The system uses feedback from the frequency detector and threshold detector to control the compressor activation. By continuously monitoring the drive signal frequency and comparing it to the threshold, the system intelligently determines when compression should be applied, allowing it to maintain high sound pressure levels when safe and reduce gain only when necessary to prevent transducer damage.
3Reliability
If a fixed voltage threshold is used for compression activation, then the transducer is protected in free air conditions, but the transducer is over-constrained when the ear cup is not completely sealed
Solution Approach 1:
The invention changes the compression threshold parameter from a fixed voltage value to a frequency-dependent voltage value. This parameter change allows the threshold to vary based on operating conditions, providing appropriate protection in free air while avoiding over-constraint when the ear cup is partially sealed. The frequency-dependent threshold adapts to the different acoustic loading conditions encountered in different seal scenarios.
Solution Approach 2:
The system transitions from a static fixed threshold to a dynamic frequency-dependent threshold. This dynamic threshold adapts to the operating conditions by responding to frequency changes in the drive signal, allowing the system to maintain optimal protection levels across different seal conditions rather than being optimized for only free air conditions.
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 enables ANR headsets to generate sound pressure levels 20dB higher than conventional headsets before reaching maximum displacement limits, while protecting the transducer from over-excitation, and adapts to different seal conditions, ensuring effective noise cancellation.
Implementation Method 1
the displacement sensing circuitry generates a corresponding displacement signal in response to a change in capacitance between the voice coil and the magnetic structure
Implementation Method 2
The noise cancelling assembly feeds the noise-cancelling signal to the electroacoustic transducer amplifier, which, in turn, combines the noise-cancelling signal with desired audio from an audio source
Implementation Method 3
The air captured between the user's ears and each electroacoustic transducer acts as a spring having a relatively high spring constant such that the air reduces displacement or excursion of each electroacoustic transducer during operation
Data Source
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AI summary
A method for adjusting the performance of an electroacoustic transducer includes receiving, by gain adjustment circuit, a displacement signal corresponding to a relative motion between a magnetic structure of the electroacoustic transducer and a voice coil of the electroacoustic transducer. The method includes detecting, by the gain adjustment circuit, a displacement signal value of the displacement signal as one of meeting or exceeding a displacement signal threshold. The method includes modifying, by the gain adjustment circuit, a loop gain of an active noise reduction loop associated with the electroacoustic transducer when the displacement signal value of the displacement signal one of meets or exceeds the displacement signal threshold.