Sound source with adjustable directivity

Abstract

Omni-directional sound sources are used to measure room-acoustical parameters in accordance with ISO 3382. To record a detailed room impulse response (RIR) with the aim of auralization, an extended frequency range is required that is not covered by the often-used building acoustics sound sources. To obtain this target, a loudspeaker with dedicated sources for low, mid, and high frequencies was designed, providing a smooth omni-directionality up to 6 kHz and a usable frequency range from 40 Hz up to 20 kHz. However, a realistic auralization of sources like musical instruments is not possible with an omni-directional measured RIR. To include the directional characteristics of instruments in the measuring setup, the directivity of the sound source has to be frequency dependent and must be matched to the (measured) directivity of the real instrument. This can be obtained by using a dodecahedron loudspeaker with independently operating systems and an appropriate complex FIR filtering of the frequency response of each driver. The directivity is a result of parameters like magnitude and phase and the interference sum of all systems. To create the appropriate directivity, optimization algorithms are used to achieve minimum error between measured and adapted directivity.