Performance of active feedforward control systems in non-ideal, synthesized diffuse sound fields

Area of Science:

• Acoustics
• Vibration and Control

Background:

• Sound transmission loss facilities use diffuse sound fields to test panel structures.
• Non-ideal diffuse sound fields in these facilities can deviate from ideal conditions.
• Active feedforward control systems rely on coherent disturbance source information.

Purpose of the Study:

• Evaluate spatial correlation and coherence of ideal and non-ideal diffuse sound fields.
• Assess the impact of non-ideal sound fields on active feedforward control performance.
• Investigate an aircraft sidewall active control system in a transmission loss facility.

Main Methods:

• Experimental testing of an aircraft-typical double panel system with active sidewall lining.
• Comparison of experimental results with simulations of a generic double panel system under ideal diffuse sound fields.
• Analysis of spatial correlation and coherence for varying numbers of sound sources and signal processing.

Main Results:

• The number of independent noise sources depends on the diffuse sound field type and signal processing sample lengths.
• Experimental and simulation results for diffuse sound fields are compared.
• An inverse relationship was found between the number of reference sensors and control filter length for achieving desired control performance.

Conclusions:

• Non-ideal diffuse sound fields significantly affect active control system performance.
• Optimizing the number of sound sources and signal processing is crucial for accurate acoustic testing.
• Reducing the number of reference sensors through longer control filters enhances active noise control efficiency in structures like aircraft sidewalls.