Active Acoustics with a Phase Cancelling Modal Reverberator

Abstract

Active acoustics (AA) systems are used to electronically modify the acoustics of a room (e.g., in live music venues). AA systems have an inherent feedback component and can suffer from instability and coloration artifacts resulting from too high feedback gains. State-of-the-art methods can improve system stability and coloration, usually at the cost of complex implementations and long parameter-tuning sessions. They can also cause sound artifacts due to time-varying components, limiting the enhancement at low frequencies. This work proposes a time-invariant feedback attenuation method for low frequencies based on a modal reverberator. The attenuation is achieved through destructive acoustic interference, obtained via phase shifts between the input and output signals. The analyzed frequency range is 0–500 Hz, where the room transfer functions are considered highly invariant over time. The results show a gain-before-instability increase of more than 5 dB for a modal reverberator with high mode density in this frequency range. The improvement is also stable for low-magnitude changes in the room transfer functions over time. The proposed method provides a robust AA system with artificial reverberation for the low-frequency range and can be used alongside other established methods.