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Coherent active methods for applications in room acoustics.
The Journal of the Acoustical Society of America
|October 1, 1985
Summary
Active acoustic wall linings can control room reverberation time by adjusting the reflection coefficient. This coherent active system uses loudspeakers and microphones to manipulate sound reflections, offering new possibilities for acoustic control.
Area of Science:
- Acoustics
- Electroacoustics
- Room Acoustics
Background:
- Passive sound absorbers are ineffective at low frequencies for reverberation control.
- Active sound systems offer more versatile reverberation management.
- Coherent active systems allow for both sound absorption and reverberation time lengthening.
Purpose of the Study:
- To develop and evaluate a coherent active wall lining for adjustable reverberation control.
- To investigate the feasibility of controlling the reflection coefficient using electroacoustic methods.
- To address challenges in extending active control from 1D to 3D sound fields.
Main Methods:
- A coherent active wall lining composed of loudspeakers, microphones, and control electronics was designed.
- A 1D experimental device was used to test reflection coefficient control below 1000 Hz.
- A 3x3 loudspeaker array and computer simulations were employed for 3D analysis.
Main Results:
- Reflection coefficients from nearly zero to 1.5 were achieved in the 1D case.
- The amplitude reflection coefficient was adjustable between 10% and 200% in 3D for sinusoidal waves.
- Nearfield effects were identified as a challenge for 3D extension.
Conclusions:
- Coherent active wall linings show promise for precise control of room acoustics.
- Further development is needed for broadband and diffuse sound field applications.
- Integration with active diffusion control is a potential future direction.