Measuring spatial impulse responses in concert halls and opera houses employing a spherical microphone array

Abstract

Traditional methods for measuring impulse responses in rooms provide detailed time and frequency resolution, but very poor spatial information. On the other hand, when a disturbing echo or discrete reflection is found, it would be very useful to be able to understand its exact direction-of-arrival. And detailed spatial information is also required when the measured impulse responses are employed as digital filters for virtual listening tests.

The method described here is based on the usage of a small spherical microphone array, equipped with 32 subminiature capsules (Knowles Electronics) mounted flush on the surface of a rigid sphere (70mm diameter). A set of 32x25 digital FIR filters are employed for processing the signals coming from the capsules, and deriving the 25 channels corresponding to a spherical harmonics decomposition of the sound field, up to 4th order. Proper postprocessing tools allow for plotting the spatial information contained in the measured set of 25 impulse responses, making it easy to visualize the spatial distribution of sound during the propagation.

This set can also be employed inside a special listening room, equipped with a spherical array of loudspeakers, for reconstruction faithfully the original soundfield, providing a realistic and immersive listening experience.

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Identifiers

ORCID for Filippo M. Fazi: orcid.org/0000-0003-4129-1433

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