Bob Essert continued his studies into the spatial relationships of a room.
Paper presented at the 3rd joint meeting of the Acoustical Society of America and the Acoustical Society of Japan in Honolulu, 4-6 December 1996.
Measurement of Spatial Impulse Responses with a Soundfield Microphone
“The [sound] source has a directivity function that varies with frequency and time. The room geometry governs how sound behaves in space. The listener has a perception function that depends on the temporal and spatial characteristics of the sound field.”
As concert hall designers we have a keen interest in measuring the spatial evolution of sound fields. So far, 3D impulse responses have been measured with sound intensity methods, with tetrahedral microphone arrays and with large microphone arrays. These methods are very sensitive to phase, and therefore to particulars of microphone construction and analysis bandwidth.
In this paper a method is proposed for capturing the spatial impulse response of a room by means of orthogonal cosine directivity microphones. Tests have been done with a simple figure-8 / omni microphone pair oriented in three directions, one after the other, as well as with a purpose-built Soundfield Microphone. Impulse responses are captured for each of the X, Y, Z and omni (Soundfield Bformat) channels. The directional impulse responses are then cross-correlated with the omni impulse response to construct “direction cosines” of strength with respect to the listener position, over time. Data can be mapped graphically in 3D space to visualize the evolution of the sound field; the degree of scatter in the data represents diffuseness. In addition to graphics, convincing 3-dimensional auralizations have been performed with soundfield impulse responses.
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