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Related Experiment Videos

Noise in miniature microphones.

Stephen C Thompson1, Janice L LoPresti, Eugene M Ring

  • 1Knowles Electronics, LLC, Itasca, Illinois 60143, USA. steve.thompson@knowlesinc.com

The Journal of the Acoustical Society of America
|February 28, 2002
PubMed
Summary

This study measured internal noise in miniature electret microphones for hearing aids. Electrical and thermal noise sources dominate at different frequencies, guiding future noise reduction efforts.

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Area of Science:

  • Acoustics
  • Electrical Engineering
  • Materials Science

Background:

  • Miniature electret microphones are crucial components in hearing aid manufacturing.
  • Understanding internal noise sources is essential for improving hearing aid performance.

Purpose of the Study:

  • To measure and analyze the internal noise spectrum of miniature electret microphones.
  • To identify the dominant noise sources across different frequencies.
  • To inform strategies for reducing microphone noise in the audio band.

Main Methods:

  • Empirical measurement of the internal noise spectrum.
  • Development and fitting of an analogous circuit model to experimental data.
  • Analysis of noise contributions from electrical and acoustic sources.

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Main Results:

  • The dominant noise source varies with frequency.
  • Electrical noise from amplifier circuits is dominant below 40 Hz and above 9 kHz.
  • Thermal noise from acoustic flow resistance is dominant between 40 Hz and 1 kHz.
  • Acoustic flow resistances of sound entry and propagation dominate between 1 kHz and 9 kHz.

Conclusions:

  • Internal noise in miniature electret microphones is frequency-dependent.
  • Targeting specific electrical and acoustic noise sources is necessary for audio band noise reduction.
  • A prototype microphone with reduced acoustical noise was developed and evaluated.