Matching early reflections of simulated and measured RIRs by applying sound-source directivity filters

Acoustic measurements are susceptible to various sources of measurement uncertainty. One significant factor is loudspeaker directivity, which introduces temporal smearing and spectral coloration into room impulse responses (RIRs), predominantly influencing early reflections. Such an artifact affects parametric processing and perceptual evaluation of RIRs and lowers the measurement reproducibility. This study evaluates the impact of loudspeaker directivity on measured RIRs. We acquire directivity filters via measurements in an anechoic chamber, utilizing a custom-made microphone arc. Subsequently, we both capture a series of RIRs in a typical reverberant room and simulate corresponding RIRs with the image-source method (ISM). By convolving the simulations with the correct directivity filters, we match the early reflections of measured and simulated RIRs. Examining the cross-correlation between the simulated and measured RIRs reveals a pronounced likeness for first-order reflections, indicating a substantial influence of the loudspeaker directivity on recorded RIRs. This study is a step towards accounting for the influence of the sound source type and position on RIRs, resulting in better-informed acoustic measurements and higher fidelity of acoustic simulations.