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The human ear cannot distinguish between two sources of sound if they happen to reach within a specific time interval, typically 0.1 seconds apart. More than this, and they are perceived as separate sources.
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A solution method for active suppression of reflections in anechoic chambers.

R Haasjes1, A P Berkhoff1,2

  • 1University of Twente, Faculty of Engineering Technology, Applied Mechanics and Data Analysis, Drienerlolaan 5, 7522 NG Enschede, The Netherlands.

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Summary

This study introduces an active noise control method to enhance anechoic chamber performance at low frequencies. The technique effectively reduces sound reflections, improving acoustic environments.

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Area of Science:

  • Acoustics
  • Control Systems Engineering
  • Computational Physics

Background:

  • Anechoic chambers are crucial for acoustic measurements but struggle with low-frequency sound absorption.
  • Traditional methods for improving anechoic chamber performance are often inefficient at lower frequencies.
  • Active noise control (ANC) offers a potential solution for enhancing low-frequency performance.

Purpose of the Study:

  • To present a novel active noise control method for improving low-frequency performance in anechoic chambers.
  • To develop an efficient computational approach for designing ANC controllers for anechoic enclosures.
  • To validate the proposed method through simulations and real-time experiments.

Main Methods:

  • Utilized the Kirchhoff-Helmholtz integral to model sound reflection within the chamber.
  • Developed a causal frequency domain algorithm with conjugate gradient iterations to compute controller filter coefficients.
  • Employed a multiple-input multiple-output (MIMO) system for a fully coupled controller design.
  • Simulated the system using a 2D finite element model with numerous secondary sources and reference sensors.

Main Results:

  • The computational method proved efficient for designing controllers with hundreds of sources and sensors in 2D and 3D.
  • A 2D finite element simulation demonstrated the method's effectiveness with 200 secondary sources and 200 reference sensors.
  • Real-time experiments in a smaller 2D setup confirmed the suppression of wall reflections.
  • Verification microphones showed a significant reduction in reverberation time during the real-time experiment.

Conclusions:

  • The proposed active noise control method effectively improves low-frequency performance in anechoic chambers.
  • The computational approach is efficient and scalable for complex ANC systems.
  • The method's real-time applicability was successfully demonstrated, reducing reverberation time.