Evaluation of a Geometric Approach to Active Acoustics

Abstract

The classic approach to active acoustics systems, regardless of an inline, regenerative or hybrid operating principle, is to change typical acoustic parameters such as EDT, RT60 or C80. Those alterations are achieved by designing a number of feedback loops between microphones and loudspeakers or by convolving the microphone signals with a specifically designed or measured impulse response. While these strategies can achieve the desired measurement results, they neglect the three-dimensional nature of the actual auditorium and alter the audible perception of the acoustic geometry present. In a great concert hall it is not just a matter of how much absorption, reflection or diffusion is used to achieve certain acoustic goals, but also of their spatial relationships with the audience. For example, "reverberant bubbles" in front of a listener create a lack of intimacy or clarity while behind a listener they help achieve the desired spaciousness. This paper evaluates strategies to influence the audible perception of acoustic geometry by means of active acoustics. In a 50-squaremeter test lab, 36 speakers and 12 microphones are evenly distributed to create a number of acoustic settings with different spatial characteristics. To evaluate the settings, standard measurements are made according to ISO 3382 and extended to 3D space using higher-order Ambisonics. In addition a survey is conducted by a test group of musicians, tonmeisters and acousticians.