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Generalized radiation modes and microphone arrays for close-talking.

Tsutomu Kaizuka1, Shuzo Terauchi1

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This study introduces a new method for designing microphone arrays to selectively measure near-field sound, enhancing signal quality in devices like mobile phones. The approach maximizes the near-to-far sound ratio for clearer audio capture.

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Area of Science:

  • Acoustics
  • Signal Processing
  • Array Design

Background:

  • Selective near-field sound measurement is crucial for improving signal-to-noise ratio in close-talking applications.
  • Existing methods may not optimally distinguish near-field from far-field sound.
  • Mobile phones and similar devices benefit from enhanced audio capture.

Purpose of the Study:

  • To apply the theory of generalized radiation modes for designing microphone arrays.
  • To maximize the near-to-far sound ratio for selective near-field sound measurement.
  • To develop a method for optimizing microphone array performance in close-talking scenarios.

Main Methods:

  • Formulating generalized radiation modes as a generalized eigenvalue problem.
  • Relating eigenvalues to the near-to-far ratio and eigenvectors to modal shapes (microphone amplitudes/phases).
  • Designing the microphone array based on the eigenvector with the largest eigenvalue.

Main Results:

  • The real eigenvalue directly corresponds to the near-to-far ratio for each mode.
  • The real eigenvector defines the optimal amplitudes and phases for individual microphones.
  • Computer simulations verified the theory and demonstrated effectiveness.

Conclusions:

  • The proposed method effectively designs microphone arrays for selective near-field sound measurement.
  • Maximizing the near-to-far ratio enhances signal quality in close-talking applications.
  • The approach offers advantages over conventional gradient microphones, as shown in numerical examples.